Handout CXL AJKdraft - American Society of Cataract and

Transcription

A. John Kanellopoulos, MD- 2709, ASCRS San Diego 2015
Laboratory science
High-irradiance CXL combined with myopic LASIK:
flap and residual stroma biomechanical properties
studied ex-vivo
Handout
Collagen Crosslinking: Evolving Indications and Technology,
Applications, Results, and Complication Management
Anastasios John Kanellopoulos,1,2 George Asimellis,1 Joseph B Ciolino,3
Borja Salvador-Culla,3 James Chodosh3
Senior Instructor: Gregory J. Pamel, MD
1
Laservision.gr Eye Institute,
Athens, Greece
Department of
Ophthalmology, New York
University Medical School,
New York, New York, USA
3
Department of Cornea &
Refractive Surgery, Harvard
Medical School, Massachusetts
Eye & Ear Infirmary, Boston,
Massachusetts, USA
2
Instructors: A. John Kanellopoulos, MD
Doyle Stulting, MD
Eric Donnenfeld, MD
Soosan Jacob, MD
ABSTRACT BODY:
Course Description: Course will present management of cornea ectasia (keratoconus/
post-refractive surgery). Surgical treatment modalities utilized internationally will be
presented, including: CXL with UVA in order to halt ectasia, combined with customised
excimer laser ablation, and topography customized CXL applications. These alternatives
to Intracorneal ring segment implantation, lamellar grafts, penetrating graft will be
analyzed. Early and late complications will be presented and discussed.
Correspondence to
Dr Anastasios John
Kanellopoulos, Department of
Ophthalmology, NYU Medical
School, New York, NY, USA;
Laservision.gr Clinical Research
Eye Institute, 17 Tsocha Street,
Athens 11521, Greece;
[email protected]
Received 19 November 2014
Revised 28 January 2015
Accepted 15 February 2015
Educational Objective: Attendees will share our vast experience in managing
progressive keratoconus and post-LASIK ectasia in order to visually rehabilitate these
patients.
ABSTRACT
Background/aims To evaluate ex vivo biomechanical
and enzymatic digestion resistance differences between
standard myopic laser in-situ keratomileusis (LASIK)
compared with LASIK+CXL, in which high-irradiance
cross-linking (CXL) is added.
Methods Eight human donor corneas were subjected
to femtosecond-assisted myopic LASIK. Group A (n=4)
served as a control group (no CXL). The corneas in
LASIK+CXL group B were subjected to concurrent
prophylactic high-irradiance CXL (n=4). Saline-diluted
(0.10%) riboflavin was instilled on the stroma,
subsequently irradiated with UV-A through the
repositioned flap. The cornea stroma and flap specimens
were separately subjected to transverse biaxial resistance
measurements; biomechanical differences were assessed
via stress and Young’s shear modulus. Subsequently, the
specimens were subjected to enzymatic degradation.
Results For the corneal stroma specimen, stress at
10% strain was 128±11 kPa for control group A versus
293±20 kPa for the LASIK+CXL group B (relative
difference Δ=+129%, p<0.05). The stress in group B
was also increased at 20% strain by +68% ( p<0.05).
Shear modulus in group B was increased at 10% strain
by +79%, and at 20% strain by +48% (both statistically
significant, p<0.05). The enzymatic degradation time to
dissolution was 157.5±15.0 min in group A versus
186.25±7.5 min in group B (Δ=+18%, p=0.014). For
the flaps, both biomechanical, as well as enzymatic
degradation tests showed no significant differences.
Conclusions LASIK+CXL appears to provide significant
increase in underlying corneal stromal rigidity, up to
+130%. Additionally, there is significant relevant
enzymatic digestion resistance confirmatory to the above.
LASIK flaps appear unaffected biomechanically by the
LASIK+CXL procedure, suggesting effective CXL just
under the flap.
INTRODUCTION
To cite: Kanellopoulos AJ,
Asimellis G, Ciolino JB, et al.
Br J Ophthalmol Published
Online First: [ please include
Day Month Year]
doi:10.1136/bjophthalmol2014-306411
Corneal collagen cross-linking (CXL) has been clinically employed for stabilising progressive keratectasia.1 2 This photochemical reactive process is
induced by peak 365 nm ultraviolet (UV-A) radiation absorbed by riboflavin, a photosensitive
vitamin B2 molecule. The procedure is broadly
known as corneal cross-linking—despite the fact
that there are some reports suggesting that the
mechanism responsible for biomechanical strengthening3 4 within the stroma is related not to interlamellar cohesion increase, but to inter-fibrillar and
intra-fibrillar cohesion.5 In addition, increased
collagen resistance against enzymatic degradation
has been associated with CXL.6–8
We have introduced an alternative CXL application, adjuvant to myopic laser in-situ keratomileusis
(LASIK+CXL). The application aims to improve
long-term keratometric stability9 and to reduce
regression likelihood following moderate and high
myopic LASIK10 by proactively restoring corneal biomechanical strength.11 Riboflavin solution is briefly
applied on the exposed stromal bed at the completion of the excimer ablation; the flap is then repositioned, followed by superficial UV-A irradiation.12 13
To the best of our knowledge, the biomechanical
and/or enzymatic degradation resistance modulations achieved via CXL application concurrent with
LASIK have not been studied in human corneas.
The purpose of this study is to evaluate ex-vivo biomechanical and enzymatic degradation resistance
differences in such application.
MATERIALS AND METHODS
Eight human donor corneas were involved,
obtained by the Eye Bank for Sight Restoration Inc
(New York, USA), an accredited member of the
Eye-Bank Association of America. The corneas
were donated by eight different donors (four men,
four women) of average age 62.0±9.5 (43–72)
years, stored in 4°C OptiSol solution (Bausch
+Lomb, Rochester, New York, USA).
Surgical technique
All corneas were subjected to femtosecond-laser
assisted myopic treatment. The corneas were
mounted on an artificial anterior chamber (Baron,
Katena Products, Inc, Denville, New Jersey, USA).
Flaps (120 μm thick, 8.5 mm diameter) were
created with the WaveLight FS200 femtosecond
laser (Alcon Surgical, Ft Worth, Texas, USA),
observing standard docking, applanation and
vacuum-suction procedures (figure 1A). After flap
lifting (figure 1B), the WaveLight EX500 excimer
laser (Alcon) was employed to create a −8.00 D
myopic ablation over a 6.5 mm diameter optical
zone (figure 1C). During the procedure, interferometric pachymetry embedded in the EX500 provided corneal thickness data.
Isotonic saline 0.1% riboflavin solution (Vibex
Rapid, Avedro Inc, Waltham, Massachusetts, USA)
was instilled on the exposed stromal bed afforded by
the lifted flap (figure 1C). Soaking time was 1 min
(figure 1E); then excess riboflavin was wiped from
the cornea surface. Special care was taken to minimise
potential riboflavin soaking to the folded LASIK flap.
Kanellopoulos AJ, et al. Br J Ophthalmol 2015;0:1–7. doi:10.1136/bjophthalmol-2014-306411
www.brilliantvision.com
1
Laboratory science
Laboratory science
Table 1 Biomechanical comparative measurements between the two groups
Stress
Units: kPa
@ 10% strain
Group A (control)
Group B (CXL)
Δ
p
t
128.0
293.4
129%
0.015
−3.33
Young’s shear modulus
@ 20% strain
±11.3
±19.9
804.1
1349.5
68%
0.025
−2.96
Units: MPa
@ 10% strain
±30.9
±46.1
3.7
6.6
79%
0.019
−3.18
@ 20% strain
±2.5
±2.4
9.5
14.0
48%
0.035
−4.62
±1.9
±5.2
Δ, relative (%) difference between metrics; p, Student t test p value; t, Student t test t value. Results from corneal stroma specimens.
Specimens were observed every 30 min until complete dissolution was achieved. The time to complete dissolution of the
stromal and flap specimens was recorded.
Data analysis
Figure 1 Schematic of the surgical procedure LASIK combined with prophylactic high-irradiance corneal cross-linking (LASIK+CXL).
The corneas were then randomly formed into two groups,
four in each. Control group A received no further treatment.
Group B (LASIK+CXL) was subjected to cross-linking: with the
flap repositioned, the cornea was UV-A irradiated at 30 mW/cm2
for 80 s (total fluence 2.4 J/cm2), employing the KXL device
(Avedro) (figure 1F).
The flaps were then amputated from all corneas; stroma and
flap specimens were stored back to OptiSol (4°C) until testing.
via dilution in Dubecco’s Phosphate Buffered Saline (DPBS,
Sigma-Aldrich). Stroma and flap specimens were incubated
within 1.5 mL of collagenase-A solution; the test tube racks
were placed at 37°C on a plate shaker at 175 rotations per min.
Biomechanical strength testing
The stroma specimens were prepared by razor-blade manual dissection to approximately 12×12 mm. The amputated flaps were
tested without additional preparation. Transverse biaxial load-cell
resistance measurements were accomplished by tangential shearforce employing the Biotester 5000 (CellScale Biomaterials
Testing, Waterloo, Canada). The device records the simultaneous
x-axis and y-axis displacement, applied force, and time. An integrated camera captures still, 1280×960-pixel images, which
provide precise x-displacement and y-displacement measurements, analysed by custom software (LabJoy V.9.05).14
The specimens were fixed (via random orientation) on a
4×5-tine rake arrangement clamped on their centre
3.5×3.5 mm section. The tines, of 250 μm diameter, were
spaced by 0.7 mm (figure 2). The specimens were then submerged into an isotonic saline bath, temperature controlled at
37°C, for 5 min before (for temperature stabilisation) as well as
during testing (to eliminate temperature-related variability).15
Shear rate was fixed to 4.16 μm/s. Time (s), x and y displacement (μm), and x and y force (mN) were recorded every
second.
RESULTS
In group A the donor age at the time of cornea harvest was 63.3
±13.7 years (48–72) and in group B, 60.8±4.5 years (43–69).
Biomechanical strength results
The distinct datasets during shear-strength measurements on
stroma specimens (all stroma specimens) were on average 290
±37 (240–340), while average displacement was 1205±155 μm
(1000–1416). Mean maximum applied force was 3996
2
Enzymatic digestion results
Regarding the stroma specimens, the mean time to complete dissolution in control group A was 157±15 min, while in group B
(LASIK+CXL) it was 186.2±7.5 min. The relative difference
Table 2 Biomechanical comparative measurements between the two groups
Stress
Units: kPa
@ 10% strain
Enzymatic degradation
The stroma specimens were trephined into 8.5 mm diameter
round buttons; no further processing on the amputated flaps.
A 0.3% collagenase-A solution (active agent: Clostridium histolyticum) (Sigma-Aldrich, St Louis, Missouri, USA) was prepared
Stress, a pressure metric, is the applied force (F) divided by the
cross section (A) of the tested area (F/A, units=mN/
mm2=kPa=103 Pa; MPa=106 Pa; Pa=Pascal). Strain, expressed
as percentage, is the unitless relative elongation Δx/lx (or Δy/ly,
respectively), where l is the initial length. Cross-section test area
was defined by the 3.5 mm sample length multiplied by the
respective stroma/flap thickness, respectively. Statistical analysis
and graphs of stress (expressed in kPa) in the vertical, versus
strain in the horizontal axis, were constructed using the SPSS
software V.21.0 (IBM Corporation, New York, USA). The exponential fitting for stress calculation was conducted at the 10%
and 20% strain. Linear regression fitting was performed to calculate, by means of the slope function (gradient), the stress/
strain ratio, an expression of the shear (Young’s) modulus. The
shear modulus was calculated as the gradient at 10% and 20%
strain. To ensure proper linear fit, we sought a minimum of
0.98 for the trend-line determination coefficient (r2).
Statistical significance was assessed employing Student’s t test.
p Values less than 0.05 were indicative of statistically significant
results in this study. Results are reported in the form: average
±SD (minimum to maximum).
±597 mN (3469–5247). Average value of maximum strain was
30±3% (26–34%).
The distinct datasets on flap specimens (all flap specimens)
were on average 222±18 (192–242), while average displacement was 925±74 μm (805–1008). Mean maximum applied
force was 1505±197 mN (1.242–1868). Average value of
maximum strain was 23.5±2% (21–25%).
The average number for all specimens of distinct data pairs
(vertical axis, stress and horizontal axis, strain) within the linear
phase of analysis of the stress–strain curves was 119 (95–129).
The average coefficient of determination (r2) of the trend-line
was 0.997 (0.994–0.999).
For the stroma specimens in control group A, average stress at
10% strain was 128±11 kPa and at 20% strain 804±31 kPa;
Young’s modulus at 10% strain was 3.7±2.5 MPa and at 20%
strain 9.5±1.8 MPa. In the LASIK+CXL group B, stress at 10%
strain was 293±20 kPa and at 20% strain 1350±46 kPa;
strain 14.0±5.2 MPa. The relative increase of these biomechanical properties in LASIK+CXL group B in comparison to
control group A was stress +129% and +68% for 10% and
20% strain, and Young’s modulus +79% and +48%, respectively. All differences were statistically significant (table 1).
For the flap specimens in control group A: stress at 10%
strain was 158±17 kPa and at 20% strain 1566±46 kPa;
strain 13.6±6.2 MPa. In the LASIK+CXL group B, stress at
10% strain was 182±21 kPa and at 20% strain 1534±134 kPa;
strain 11.9±4.1 MPa. The relative changes of these biomechanical properties in LASIK+CXL group B in comparison to
control group A were not statistically significant (table 2).
Figure 2 Fitting of the corneal specimens (top) and the flap (bottom)
on the BioTester device.
Group A (control)
Group B (CXL)
Δ
p
t
158.3
182.8
15%
0.084
−2.07
Young’s shear modulus
@ 20% strain
±16.8
±20.8
1566.6
1534.5
−2%
0.140
+1.7
Units: MPa
@ 10% strain
±45.9
±134.8
5.9
6.5
11%
0.095
−1.98
@ 20% strain
±3.9
±3.2
13.6
11.9
−12%
0.089
+2.02
±6.2
±4.1
Δ, relative (%) difference between metrics; p, Student t test p value; t, Student t test t value. Results from flap specimens.
3
Laboratory science
Laboratory science
Δ was +18% for group B, a statistically significant difference
( p=0.014). Regarding the flaps, the mean time to complete dissolution in group A was 68.75±17.3 min, while in group B it
was 80.0±8.1 min. The relative difference Δ was +16% for
group B, a difference which, however, was not statistically significant (table 3).
DISCUSSION
Epithelium-on, in-situ CXL is reported in the peer review literature16 17 with a significantly weaker biomechanical effect in
comparison to epi-off CXL.18 This is partially attributed to
reduced riboflavin permeability through the intact epithelium,
mainly due to its large molecular weight.19 This leads to insufficient and inhomogeneous riboflavin stromal diffusion and thus
affects UV-A transmission to deeper layers, due to increased
UV-A absorption by the superficially concentrated riboflavin.
The second issue that affects epithelium-on CXL relates to
UV-A absorption/filtering by the intact epithelium.20 Some
studies suggest absorption by the epithelium of about one-third,19
leading to less energy reaching the riboflavin-saturated stroma.
However, there are studies suggesting that human corneal epithelium and the underlying basement membrane absorb strongly
only at wavelengths smaller than 310 nm,21 22 which compares
to the peak 365 nm of the CXL-employed UV-A.
The effect of refractive surgery on corneal biomechanical
properties may be evaluated in-vivo by the corneal hysteresis
and corneal resistance factor. These indices can be assessed by
dynamic tonometry (visualisation of fast deformation of the
cornea), employing the Corvis ST (Oculus Optikgeräte GmbH,
Wetzlar, Germany) and the Ocular Response Analyser (Reichert,
Buffalo, New York, USA). Several studies have evaluated the reduction in corneal biomechanical strength following LASIK,23–26 and
following ReLEx flex and ReLEx smile procedures, suggesting
similar corneal biomechanical reduction among these laser
refractive procedures.27 28 However, there is inconclusive evidence in the peer review literature on the specificity of these
techniques in the in-vivo evaluation of the effect of corneal
cross-linking.29 30
The in-situ riboflavin application investigated in this study
naturally overcomes the above-mentioned restriction of riboflavin penetration through the intact epithelium, since it is applied
directly on the exposed stromal bed. In addition, the ex-vivo
nature of this study overcomes the potential shortcomings presented in relation to in-vivo evaluation techniques.
Our team has investigated clinically in-situ (ie, intrastromal)
CXL applications as a means to offer proactive cornea stabilisation in high-myopic LASIK.31 The long-term investigation of
epithelial thickness increase was investigated as an indirect measurement of overall corneal stability, supported by a difference in
Table 3 Enzymatic digestion time to complete dissolution
Corneas
Group A (control)
Group B (CXL)
Δ
p
t
Competing interests Consultant/advisory positions: AJK: Alcon/WaveLight,
Avedro, i-Optics, Allegran; Keramed.
Provenance and peer review Not commissioned; externally peer reviewed.
REFERENCES
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-A-induced collagen
crosslinking for the treatment of keratoconus. Am J Ophthalmol 2003;135:620–7.
Kanellopoulos AJ, Binder PS. Collagen cross-linking (CCL) with sequential
topography-guided PRK: a temporizing alternative for keratoconus to penetrating
keratoplasty. Cornea 2007;26:891–5.
Wollensak G, Iomdina E. Biomechanical and histological changes after corneal
crosslinking with and without epithelial debridement. J Cataract Refract Surg
2009;35:540–6.
Hafezi F, Kanellopoulos J, Wiltfang R, et al. Corneal collagen crosslinking with
riboflavin and ultraviolet A to treat induced keratectasia after laser in situ
keratomileusis. J Cataract Refract Surg 2007;33:2035–40.
Wollensak G, Spörl E, Mazzotta C, et al. Interlamellar cohesion after corneal
crosslinking using riboflavin and ultraviolet A light. Br J Ophthalmol
2011;95:876–80.
Spoerl E, Wollensak G, Seiler T. Increased resistance of crosslinked cornea against
enzymatic digestion. Curr Eye Res 2004;29:35–40.
Arafat SN, Robert MC, Shukla AN, et al. UV cross-linking of donor corneas confers
resistance to keratolysis. Cornea 2014;33:955–9.
Mazzotta C, Caporossi T, Denaro R, et al. Morphological and functional correlations
in riboflavin UV A corneal collagen cross-linking for keratoconus. Acta Ophthalmol
2012;90:259–65.
Kanellopoulos AJ, Asimellis G. Refractive and keratometric stability in high myopic
LASIK with high-frequency femtosecond and excimer lasers. J Refract Surg
2013;29:832–7.
Chayet AS, Assil KK, Montes M, et al. Regression and its mechanisms after laser in
situ keratomileusis in moderate and high myopia. Ophthalmology
1998;105:1194–9.
Cho M, Kanellopoulos AJ. Safety and efficacy of prophylactic ultraviolet-A-induced
crosslinking after high risk myopic photerefractive keratomy, Poster 5470/A441,
ARVO May 3–7, 2009, Florida, USA.
Kanellopoulos AJ. Long-term safety and efficacy follow-up of prophylactic higher
fluence collagen cross-linking in high myopic laser-assisted in situ keratomileusis.
Clin Ophthalmol 2012;6:1125–30.
Kanellopoulos AJ, Pamel GJ. Review of current indications for combined very high
fluence collagen cross-linking and laser in situ keratomileusis surgery. Indian J
Ophthalmol 2013;61:430–2.
Søndergaard AP, Ivarsen A, Hjortdal J. Corneal resistance to shear force after
UVA-riboflavin cross-linking. Invest Ophthalmol Vis Sci 2013;54:5059–69.
Hatami-Marbini H, Rahimi A. Effects of bathing solution on tensile properties of the
cornea. Exp Eye Res 2014;120:103–8.
Boxer Wachler BS, Pinelli R, Ertan A, et al. Safety and efficacy of transepithelial
crosslinking (C3-R/CXL). J Cataract Refract Surg 2010;36:186–8.
Magli A, Forte R, Tortori A, et al. Epithelium-off corneal collagen cross-linking
versus transepithelial cross-linking for pediatric keratoconus. Cornea
2013;32:597–601.
Leccisotti A, Islam T. Transepithelial corneal collagen cross-linking in keratoconus.
J Refract Surg 2010;26:942–8.
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
Baiocchi S, Mazzotta C, Cerretani D, et al. Corneal crosslinking: riboflavin
concentration in corneal stroma exposed with and without epithelium. J Cataract
Refract Surg 2009;35:893–9.
Podskochy A. Protective role of corneal epithelium against ultraviolet radiation
damage. Acta Ophthalmol Scand 2004;82:714–17.
Kolozsvári L, Nógrádi A, Hopp B, et al. UV absorbance of the human cornea in the
240- to 400-nm range. Invest Ophthalmol Vis Sci 2002;43:2165–8.
Ionescu AM, de la Cruz Cardona J, González-Andrades M, et al. UV absorbance of
a bioengineered corneal stroma substitute in the 240–400 nm range. Cornea
2010;29:895–8.
Kirwan C, O’Keefe M. Corneal hysteresis using the Reichert ocular response
analyser: findings pre- and post-LASIK and LASEK. Acta Ophthalmol
2008;86:215–18.
Hamilton DR, Johnson RD, Lee N, et al. Differences in the corneal biomechanical
effects of surface ablation compared with laser in situ keratomileusis using a
microkeratome or femtosecond laser. J Cataract Refract Surg 2008;34:2049–56.
Uzbek AK, Kamburoglu G, Mahmoud AM, et al. Change in biomechanical
parameters after flap creation using the intralase femtosecond laser and subsequent
excimer laser ablation. Curr Eye Res 2001;36:614–19.
Kamiya K, Shimizu K, Ohmoto F. Time course of corneal biomechanical parameters
after laser in situ keratomileusis. Ophthalmic Res 2009;42:167–71.
Pedersen IB, Bak-Nielsen S, Vestergaard AH, et al. Corneal biomechanical properties
after LASIK, ReLEx flex, and ReLEx smile by Scheimpflug-based dynamic tonometry.
Graefes Arch Clin Exp Ophthalmol 2014;252:1329–35.
Agca A, Ozgurhan EB, Demirok A, et al. Comparison of corneal hysteresis and
corneal resistance factor after small incision lenticule extraction and femtosecond
laser-assisted LASIK: a prospective fellow eye study. Cont Lens Anterior Eye
2014;37:77–80.
Bak-Nielsen S, Pedersen IB, Ivarsen A, et al. Dynamic Scheimpflug-based
assessment of keratoconus and the effects of corneal cross-linking. J Refract Surg
2014;30:408–14.
Gatinel D. The mystery of collagen cross-linking when it comes to in vivo
biomechanical measurements. J Refract Surg 2014;30:727.
Kanellopoulos AJ, Asimellis G. Epithelial remodeling after femtosecond laser-assisted
high myopic LASIK: comparison of stand-alone with LASIK combined with
prophylactic high-fluence cross-linking. Cornea 2014;33:463–9.
Elsheikh A, Anderson K. Comparative study of corneal strip extensometry and
inflation tests. J R Soc Interface 2005;2:177–85.
Sánchez P, Moutsouris K, Pandolfi A. Biomechanical and optical behavior of human
corneas before and after photorefractive keratectomy. J Cataract Refract Surg
2014;40:905–17.
Smolek MK. Interlamellar cohesive strength in the vertical meridian of human eye
bank corneas. Invest Ophthalmol Vis Sci 1993;34:2962–9.
Petsche SJ, Chernyak D, Martiz J, et al. Depth-dependent transverse shear
properties of the human corneal stroma. Invest Ophthalmol Vis Sci
2012;53:873–80.
Kanellopoulos AJ, Asimellis G, Karabatsas C. Comparison of prophylactic higher
fluence corneal cross-linking to control, in myopic LASIK, one year results. Clin
Ophthalmol 2014;8:2373–81.
Reinstein DZ, Srivannaboon S, Archer TJ, et al. Probability model of the inaccuracy
of residual stromal thickness prediction to reduce the risk of ectasia after LASIK part
II: quantifying population risk. J Refract Surg 2006;22:861–70.
Leccisotti A. Corneal ectasia after photorefractive keratectomy. Graefes Arch Clin
Exp Ophthalmol 2007;245:869–75.
Flaps
Time
Units: min
Time
Units: min
157.50
186.25
18%
0.014
−3.45
±15.00
±7.50
68.75
80.00
16%
0.0804
−2.1
±17.32
±8.16
CONCLUSIONS
Adjuvant intrastromal in-situ CXL combined with myopic
LASIK appears in ex vivo human study to be a significant biomechanical modulator.
Δ, relative (%) difference between metrics; p, Student t test p value; t, Student t test
t value.
4
epithelial remodelling, which may indicate increased biomechanical stability in myopic LASIK combined with adjuvant CXL.
In this study we conducted a human ex-vivo investigation of
the biomechanical corneal strengthening occurring during
in-situ CXL along myopic LASIK. We evaluated changes in the
stroma (and also, for the first time reported separately, the
LASIK flap) employing biaxial stress–strain measurements,
which may be considered superior to the one-dimensional
corneal strip extensiometry32 taking into account the nonuniform topographic distribution of the corneal strength
profile.33 34 We provided 10% and 20% strain values for two
reasons. First, these are the ones typically reported by other
researchers,14 in an effort to provide some form of comparison.
In addition, the stress–strain plot had adequate linearity in these
areas to enable data collection.
The depth dependence of transverse shear modulus of the
cornea, stronger at the anterior third,35 indicates that tissue
removal from this upper third may affect corneal rigidity the
most. In our study we demonstrated that the effective CXL
corneal rigidity in comparison to the non-CXL corneas that
received the same treatment was of the order of +129% stress
at 10% strain, by a statistically significant margin. Considering
that the aim of the in-situ CXL application is to provide prophylactic corneal strengthening to counter weakening due to tissue
removal, we view this very significant biomechanical effect as a
very important finding. These findings are confirmatory to our
previous clinical effects reported on myopic and hyperopic
LASIK+CXL applications.36 CXL maybe therefore be used as a
biomechanical modulator offering refractive stability following
LASIK.
There was no indication that the flaps had any statistically significant biomechanical difference by any metric employed. This
finding is a very important indicator that no actual cross-linking
of the flap occurs during our LASIK+CXL technique. There are
two main reasons that we target to avoid any cross-linking effect
on the flap. First is that the flap does not contribute to the biomechanical properties of the underlying stroma.37 38 Therefore,
there is no benefit from a potential cross-linking of the flap.
Second, and perhaps even more important, is that cross-linking
such a thin (the LASIK flap consists of ∼ 50 μm of epithelium
and ∼ 60 μm of stroma) stromal content may lead to undesirable
stromal shrinking of the flap.
Additionally, the findings in the collagen-enzymatic digestion
part of this work provide corroborative evidence of the differential effects of cross-linking on the stroma and not on the flap.
This is, to the best of our knowledge, the first manuscript presenting both techniques, bi-axial stress measurements and
enzymatic digestion, of ex-vivo human assessment of crosslinking effects.
Additional studies with larger sample size, differentiation of
UV-A irradiance, as well as extending the testing period to
longer time intervals following treatment are warranted to validate and further investigate the findings in this preliminary study.
Contributors Design and conduct of the study (AJK, GA); collection (AJK, GA,
BS-C), management (AJK, JBC, JC), analysis (AJK, GA, JBC, BS-C, JC), interpretation
of the data (AJK, GA, JBC, BS-C, JC); manuscript preparation (GA), manuscript
review (AJK, GA, JBC, BS-C, JC), manuscript approval (AJK, GA, JBC, BS-C, JC).
5
Laboratory science
6
Laboratory science
7
BASIC INVESTIGATION
Kanellopoulos et al
Corneal Collagen Cross-linking Combined With Simulation
of Femtosecond Laser–Assisted Refractive Lens Extraction:
An Ex Vivo Biomechanical Effect Evaluation
Anastasios J. Kanellopoulos, MD,*† Mark A. Kontos, MD,‡ Shihao Chen, MD, OD, MSc,§
and George Asimellis, PhD*
Purpose: To evaluate biomechanical changes induced by in situ
corneal cross-linking (CXL) with stromal pocket delivered enhanced
concentration riboflavin and high-fluence, high-energy UV-A irradiation.
CXL, high-energy CXL, higher riboflavin concentration CXL,
corneal biomechanics, Young shear modulus, corneal stress–strain
(Cornea 2015;0:1–7)
refractive correction application aiming to restore corneal
biomechanical strength has not yet been reported.
The purpose of this study was to evaluate ex vivo the
biomechanical changes resulting from a simulated refractive
lens extraction procedure combined with CXL.
This laboratory (ex vivo) study was approved by the
Laservision.gr Clinical and Research Eye Institute Ethics
Committee.
Eight human donor corneas were used in the study,
which were obtained for research purposes from the Eye
Bank for Sight Restoration Inc (New York, NY). The
corneas were donated by 8 different organ donors (4 men, 4
women), whose mean age was 64.25 6 11.96 years (range,
50–79 years).
Methods: Eight human donor corneas were subjected to intrastromal
lamellar corneal tissue removal of anterior 140-mm deep, 80-mm thick
· 5-mm diameter central stromal buttons, extracted through a 3.5-mm
width tunnel, surfacing in the superior cornea periphery. Enhanced
concentration riboflavin solution (0.25%) was instilled in the pocket.
In study group A (CXL), superficial high-fluence UV-A irradiation
was applied, whereas in control group B (no CXL), none. To
comparatively assess changes in corneal rigidity, corneal specimens
were subjected to transverse biaxial resistance measurements by
application of a unidirectional tangential shear force. Biomechanical
differences were evaluated through stress and Young shear modulus.
Results: Stress at 10% strain was 305 6 24 kPa in study group A
versus 157 6 11 kPa in control group B (relative difference D =
107%, P = 0.021). Stress at 20% strain was 1284 6 34 kPa in study
group A versus 874 6 29 kPa in control group B (D = 47%, P =
0.043). Average shear modulus in study group A at 10% strain was
6.98 6 1.12 MPa versus 4.04 6 0.85 MPa in control group B (D =
73%, P = 0.036). Average shear modulus in study group A at 20%
strain was 11.46 6 0.75 MPa versus 8.80 6 0.72 MPa in group B
(D = 30%, P = 0.047).
Conclusions: Adjunct CXL in this ex vivo simulation refractive lens
extraction procedure seems to provide significant increase in corneal
rigidity, up to +107%. These findings also support our previous
reported work on laser in situ keratomileusis combined with CXL.
Key Words: femtosecond laser, refractive lens extraction, biomechanical simulation, in situ CXL, epithelium on, high-fluence
Received for publication November 4, 2014; revision received December 15,
2014; accepted December 18, 2014.
From the *Laservision.gr Clinical and Research Eye Institute, Eye Institute,
Athens, Greece; †New York University Medical School, New York, NY;
‡Empire Eye Physicians, Spokane, WA; and §Affiliated Eye Hospital of
Wenzhou Medical University, Zhejiang, China.
A. J. Kanellopoulos holds consultant/advisory positions in Alcon/WaveLight,
Avedro, i-Optics, and Oculus and M. A. Kontos in Abbott Medical. The
remaining authors have no funding or conflicts of interest to disclose.
Reprints: Anastasios J. Kanellopoulos, MD, Laservision.gr Clinical and
Research Eye Institute, Eye Institute, 17 Tsocha St, Athens 11521, Greece
(e-mail: [email protected]).
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Cornea ! Volume 0, Number 0, Month 2015
C
orneal collagen cross-linking (CXL) has been clinically
used for stabilizing progressive keratectasia.1,2 A photochemical reactive process induced by 365-nm UV-A light in
the presence of riboflavin, a photosensitive molecule, results
in increased intrafibrillar and interfibrillar covalent bonds3 and
stromal collagen resistance against enzymatic degradation.4,5
The increased stromal biomechanical strength and lamellar
compaction lead to corneal stabilization.6
The original protocol Dresden technique1 requires
corneal epithelium removal (epithelium off) and anterior
stromal saturation with riboflavin solution. Aiming to address
the significant morbidity and postoperative pain associated
with epithelial removal,7 several alternatives have been
proposed. One such alternative is to keep the epithelium in
place and attempt to loosen the epithelial tight junctions to
facilitate riboflavin diffusion with prolonged use of topical
anesthetics, in a procedure termed “epithelium-on” CXL.8
Our team has introduced alternative CXL techniques using
higher fluence, shorter duration UV-A irradiation, and
administration of riboflavin solution in an anterior intrastromal lamellar pocket created with a femtosecond laser.9
A subsequent CXL alternative application we also
presented (Kanellopoulos AJ Prophylactic, ultraviolet
a cross-linking combined at the completion of high risk
myopic LASIK cases. Subspecialty Day Paper presentation,
American Academy of Ophthalmology Annual Meeting, Nov
8, 2008, Atlanta, GA) aimed to proactively restore corneal
biomechanical stability10 in myopic laser in situ keratomileusis (LASIK) corrections.11–13 Riboflavin is applied on the
exposed stromal bed afforded by the open LASIK flap; the
flap is then repositioned, followed by UV-A irradiation of
the riboflavin-soaked stroma through the flap.14,15
Recently reported refractive error correction procedures
involve intrastromal tissue dissection performed solely by
a femtosecond laser.16,17 Although the mechanism of stromal
tissue reduction in these procedures is different from LASIK,
the issue of potential biomechanical weakening, particularly
in attempted high myopic corrections has been modeled18 and
investigated clinically.19 The combination of CXL with such
www.corneajrnl.com |
1
Copyright ª 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.
Experimental Technique
All corneas were subjected to creation and removal of
a central lamellar intrastromal button through a customdesigned application consisting of a double intrastromal bed
cut. A WaveLight FS200 femtosecond laser (Alcon Surgical,
Ft Worth, TX) was used for this purpose. The corneas were
mounted on an artificial chamber (Baron; Katena Products,
Inc, Denville, NJ). To achieve high precision intrastromal
cuts, we implemented standard docking, applanation, and
vacuum suction procedures appropriate for the use of the
FS200 laser along with the clear cone–patient interface.20
Subsequently, the following 2 FS200 procedures were
applied:
1. Procedure A, a circular posterior lamellar bed dissection
of 9-mm diameter 220-mm depth from the anterior
corneal surface (Fig. 1A). To achieve this, the “flap”
mode with no side cut was used. A 0.4-mm wide and
3.0-mm long canal was designed to serve as the channel
through which the “button” to be created would be
extracted.
2. Procedure B, a circular anterior lamellar dissection of
5-mm diameter 140-mm depth (Fig. 1B). To achieve
this, the “posterior lamellar” mode was used. In
addition, the circumferential “side-wall” cut was
extended to 100 mm to ensure that the vertical
dissections of the cut would transcend the posterior
lamellar level.
The combination of these 2 procedures resulted in the
creation of an intralamellar “button,” 5-mm diameter, 80-mm
thick, located 140 mm inside the cornea (Fig. 1C). In addition,
a “channel” was created, enabling button extraction. The
button was extracted using a Sinskey hook and toothless
FIGURE 1. A, Posterior lamellar cut: left, detail from the system software report, right, schematic drawing; B, Superior lamellar
cut: left, detail from the system software report, right, schematic drawing; C, Intralamellar “button” creation: left, detail from the
system software report, right, schematic drawing.
2
| www.corneajrnl.com
In Situ CXL Corneal Biomechanics
Kanellopoulos et al
forceps (Katalyst Surgical, Chesterfield, MO) for the lamellar
dissections (button separation) and forceps for button grip and
extraction. Before and after the procedure, corneal thickness
and anterior surface keratometry were evaluated through
anterior segment optical coherence tomography (RtVue-100;
Optovue Inc, Fremont, CA) and Scheimpflug imaging
(Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany).
The corneas were then randomly assigned to 2 groups
of 4 each. In study group A, a subsequent high-fluence CXL
was applied. A 0.25% isotonic saline-diluted riboflavin
solution (Vibex Xtra; Avedro Inc, Waltham, MA) was
injected in the pocket afforded by the removed button
through the channel used for its removal. Soaking time was
1 minute, followed by rinsing of excess riboflavin from the
corneal surface. UV-A illumination of 45 mW/cm2 was
applied for 2 minutes and 40 seconds (intended energy,
7.2 J/cm2). The KXL-I cross-linking device (Avedro Inc)
was used for this purpose. In the corneas belonging to group
B, the same riboflavin solution was injected in the pocket,
but no UV-A was irradiated, with the intent to serve as
a control group.
Data Collection and Analysis
A central square block (approximately 12 · 12 mm)
was obtained from each treated corneal specimen using
a disposable razor blade. A Biotester 5000 device (CellScale
Biomaterials Testing, Waterloo, Canada) was used to provide
biaxial resistance testing.
The specimens were fixed (random orientation) on a 4 · 5
tine rake arrangement (Fig. 2) at their center 3.5 · 3.5 mm
section. The tines (250-mm diameter) were spaced apart by
0.7 mm. The specimens on the fixation unit were submerged
into an isotonic saline bath, temperature controlled at 37°C for
5 minutes before testing (to allow for temperature stabilization),
as well as during testing (to eliminate any temperature-related
variability).21 Shear rate was fixed to 4.16 mm/s. The following
data, time (s), x and y size (mm), x and y displacement (mm),
x and y force (mN), and x and y strain (unitless), were recorded
every second. An integrated CCD camera captured still images
at 1280 · 960 pixel resolution, analyzed by custom software
(LabJoy v. 9.05; CellScale Biomaterials Testing).22
Linear regression fitting using Microsoft Excel 2013
(version 15.0; Microsoft, Redmont, WA) was applied on the
linear section of the loading curve to calculate, by means of the
slope function (gradient), the stress–strain ratio, an expression
of the shear (Young) modulus E. To ensure proper linear
relationship fit, a minimum value coefficient of determination
(R2) of the trend line of 0.98 was sought. Stress at 10% and
20% strain was recorded. Young shear modulus E was
calculated as the gradient at the vicinity of 10% and 20%
strain at the stress–strain graph. The following definitions have
been adopted: stress, a pressure metric, as the applied force F
divided by cross-section A of the corneal specimen test area
(F/A, units = mN/mm2 = kPa = 103 Pa; MPa = 106 Pa; where
Pa is Pascal, SI unit for pressure), and strain as the unitless
relative elongation (Dx/l), expressed as percentage. Crosssection of the test area was defined by 3.5-mm x (or
y, respectively) width multiplied by the corneal thickness.
FIGURE 2. A, Initial picture during stress–strain measurement
indicating the dual axis grip on the cornea specimen. B, The
same cornea specimen at the completion of the test, 268
seconds later. The cornea was stretched in both directions
(x and y) by 1.116 mm.
RESULTS
In all procedures performed, the intralamellar button
creation by FS200 femtosecond laser was without incident.
Completion time, including corneal docking lamellar dissection by the laser was less than 1 minute in each case. The
manual corneal button removal through the channel created,
despite being a novel procedure, was also uncomplicated.
Fig. 3 provides an example of postoperative optical
coherence tomography imaging of a cornea in group A,
indicating the hyperreflection line of the CXL, as well as
corneal and epithelial pachymetry. Average preoperative
central corneal thickness for study group A was 567.5 6
21 mm versus 557 6 19 mm for control group B (P = 0.721).
Average postoperative central corneal thickness for study
group A was 447.5 6 25 mm versus 451.2 6 22 mm for
control group B (P = 0.875). Fig. 4 presents an example of
axial curvature map and example of differences between
postoperative and preoperative axial curvature, obtained by
Scheimpflug imaging.
3
FIGURE 3. Top, optical coherence tomography–derived meridional cross-section of CXL cornea, indicating a clear hyperreflection
line along the cross-linked stroma. Bottom, optical coherence tomography–derived corneal and epithelial pachymetry of the same
cornea.
The distinct data sets during each shear strength
measurement were on average 273 (range, 233–326) and
the average displacement was 1129 mm (range, 971–1357).
Mean maximum applied force was 2950 mN (range, 2009–
3370). Average value of maximum strain (relative elongation)
was 27.5% (range, 24.3%–32.5%).
The linear phase of analysis of the stress–strain curves
was sought for all corneas in both groups. The average
number of distinct data pairs (y axis, stress and x axis, strain)
within the linear phase in each analysis was 112 (range, 89–
125). The average coefficient of determination (R2) of the
trend line was 0.996 (range, 0.994–0.999).
Table 1 summarizes results from the biomechanical
data analysis. Stress at 10% strain was 305.04 6 24.34 kPa in
study group A versus 157.00 6 11.42 kPa in control group B
(relative difference D = 107%, P , 0.021). Stress at 20%
strain was 1284.79 6 34.20 kPa in study group A versus
874.38 6 29.40 kPa in control group B (relative difference
D = 47%, P , 0.043).
Average shear modulus in CXL group A at 10% strain
was 6.98 6 1.12 MPa versus 4.04 6 0.85 MPa in control
group B (relative difference D = +73%, P = 0.036). Average
shear modulus in CXL group A at 20% strain was 11.46 6
0.75 MPa versus 8.80 6 0.72 MPa in control group B
(relative difference D = +30%, P = 0.047).
4
DISCUSSION
The Dresden standard protocol CXL involves epithelial
removal, superficial riboflavin instillation, and 365-nm UV-A
FIGURE 4. Scheimpflug imaging axial curvature maps from a cornea in group A. Preoperative (left), postoperative (middle), and
difference (right) maps.
fluence of 5.4 J/cm,1,23 aiming to address inherently biomechanically weakened thin corneas suffering from keratectasia. Subsequent modifications of this original technique, by
maintaining intact epithelium (epithelium-on CXL), have
been considered.
The challenges faced in these alternative applications
are related to epithelial permeability and thus insufficient/
inhomogeneous diffusion of riboflavin to the stroma, mainly
because of the large molecular weight of riboflavin.24,25 Even
higher concentration (0.5%) riboflavin solutions may not
facilitate improved results in comparison with the standard
(0.1%) concentration.26
The second issue is epithelial and Bowman membrane
absorption/filtering of UV-A that could lead to lesser energy
delivered to riboflavin-saturated stroma, as effective absorption by riboflavin at the superficial layers inhibits UV-A
transmission.27 Some studies indicate approximately onethird epithelial UV-A absorption,24 whereas other studies
suggest that human corneal epithelium and the underlying
basement membrane absorb strongly only at wavelengths less
than 310 nm.28,29
The efficacy of multiple epithelium-on CXL techniques may warrant standardization and extensive investigation. Ex vivo evaluation of in situ (through a stromal
pocket) CXL in porcine corneas (which do not have Bowman
membrane) indicates that the biomechanical strengthening is
reduced by approximately 50%, in comparison with standard
protocol CXL.30 There is thus inconclusive evidence in the
peer-reviewed literature on the aspect of efficacy of some
epithelium-on CXL variations.3,8,26,31,32
The in situ riboflavin application naturally overcomes
the first of the 2 obstacles, related to riboflavin penetration
through the intact epithelium and in acting as a “blocking”
agent against UV-A propagation. This is because the
epithelium and Bowman layer, that the UV-A light has to
transcend, are not soaked in riboflavin.
In this study, we conducted an ex vivo investigation to
biomechanically address this issue, as in vivo biomechanical
measurements, in our experience, have shown low specificity
and sensitivity. We investigated the effect on corneal biomechanical properties by using objective biaxial stress–strain
measurements. This technique may be superior to corneal
strip extensiometry used in earlier experiments,33 considering
the nonuniform topographic distribution of the corneal
strength profile34 due to collagen anisotropy.35 To address
the fact that corneal shear modulus naturally varies along
different corneal meridians, the specimens were also randomly oriented during testing.
It is known that the cornea is stronger at the anterior
third.36 This transverse depth dependence37 suggests that
tissue removal from the upper third may affect corneal
rigidity the most. In our study, we demonstrated that the
effective stromal rigidity increase in the cross-linked corneas
was of the order of 100% at the 10% strain point, in
TABLE 1. Biomechanical Comparative Measurements Between the 2 Groups
Stress, kPa
10% strain
Group A (CXL)
Group B (control)
D
P
305.04
147.39
107
0.021
D
623.30
610.72
Young’s Shear Modulus, MPa
20% strain
1284.79
874.38
47
0.043
10% strain
D
634.20
629.40
6.98
4.04
73
0.036
D
61.12
60.85
20% strain
11.46
8.80
30
0.047
D
60.75
60.72
D, Relative difference (%) between metrics; P, Student test P value.
5
Kanellopoulos et al
comparison with the non-CXL corneas that received the
same treatment. This is an important finding, considering
that the aim of in situ CXL was to exactly provide corneal
stiffening to compensate for stromal weakening due to
anterior stromal tissue removal, and thus to offer longterm corneal stability.
The data in this study provide substantial ex vivo
evidence that significant stromal strengthening may occur
even when UV-A is projected through the intact corneal
epithelium, Bowman membrane, and superficial stroma, to
reach the underlying riboflavin-soaked stroma. These findings
support our previous clinical investigation conducted in vivo
of refractive stability in high myopic LASIK cases treated
with prophylactic CXL,12 as well as the compelling steepening refractive effect stabilization in clinical hyperopic LASIK
cases treated with prophylactic CXL.
Recent advances in variable fluence, customized pattern
CXL may add another element to potential applications of this
proposed technique: “hyperopic” style pattern in situ CXL may
be combined to enhance cornea asphericity, overcorrection, and
even address future presbyopia in myopic refractive lens
extraction.38 “Myopic” style pattern in situ CXL used in similar
manner may address residual or regressing refractive error in
high myopia refractive lens extraction.
CONCLUSIONS
Adjunct intrastromal cross-linking may be a valuable
biomechanical modulator providing titratable increased rigidity in corneas undergoing intrastromal tissue removal such as
femtosecond laser refractive intracorneal lenticular extraction.
These data support our previous reported findings in LASIK
combined with CXL.
REFERENCES
1. Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a-induced
collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol.
2003;135:620–627.
2. Hafezi F, Kanellopoulos J, Wiltfang R, et al. Corneal collagen crosslinking with riboflavin and ultraviolet A to treat induced keratectasia after
laser in situ keratomileusis. J Cataract Refract Surg. 2007;33:
2035–2040.
3. Wollensak G, Iomdina E. Biomechanical and histological changes after
corneal crosslinking with and without epithelial debridement. J Cataract
Refract Surg. 2009;35:540–546.
4. Spoerl E, Wollensak G, Seiler T. Increased resistance of crosslinked
cornea against enzymatic digestion. Curr Eye Res. 2004;29:35–40.
5. Arafat SN, Robert MC, Shukla AN, et al. UV cross-linking of
donor corneas confers resistance to keratolysis. Cornea. 2014;33:
955–959.
6. Mazzotta C, Caporossi T, Denaro R, et al. Morphological and functional
correlations in riboflavin UV A corneal collagen cross-linking for
keratoconus. Acta Ophthalmol. 2012;90:259–265.
7. Bakke EF, Stojanovic A, Chen X, et al. Penetration of riboflavin and
postoperative pain in corneal collagen crosslinking: excimer laser
superficial versus mechanical full-thickness epithelial removal. J Cataract Refract Surg. 2009;35:1363–1366.
8. Stojanovic A, Chen X, Jin N, et al. Safety and efficacy of epithelium-on
corneal collagen cross-linking using a multifactorial approach to
achieve proper stromal riboflavin saturation. J Ophthalmol. 2012;
2012:498435.
9. Kanellopoulos AJ. Collagen cross-linking in early keratoconus with
riboflavin in a femtosecond laser-created pocket: initial clinical results. J
Refract Surg. 2009;25:1034–1037.
6
10. Chayet AS, Assil KK, Montes M, et al. Regression and its mechanisms
after laser in situ keratomileusis in moderate and high myopia.
Ophthalmology. 1998;105:1194–1199.
11. Kanellopoulos AJ, Asimellis G. Refractive, and keratometric stability in
high myopic LASIK with high-frequency femtosecond and excimer
lasers. J Refract Surg. 2013;29:832–837.
12. Kanellopoulos AJ, Asimellis G. Epithelial remodeling after femtosecond
laser-assisted high myopic LASIK: comparison of stand-alone with
LASIK combined with prophylactic high-fluence cross-linking. Cornea.
2014;33:463–469.
13. Kanellopoulos AJ, Asimellis G. Epithelial remodeling after partial
topography-guided normalization and high-fluence short-duration crosslinking (Athens protocol): results up to 1 year. J Cataract Refract Surg.
2014;40:1597–1602.
14. Kanellopoulos AJ. Long-term safety and efficacy follow-up of
prophylactic higher fluence collagen cross-linking in high myopic
laser-assisted in situ keratomileusis. Clin Ophthalmol. 2012;6:
1125–1130.
15. Cho M, Kanellopoulos AJ. Safety and efficacy of prophylactic ultravioletA-induced crosslinking after high risk myopic photorefractive keratotomy.
Poster presented at: 5470/A441, ARVO; Fort Lauderdale, FL. May 3–7,
2009; FN.
16. Sekundo W, Kunert KS, Blum M. Small incision corneal refractive
surgery using the small incision lenticule extraction (SMILE)
procedure for the correction of myopia and myopic astigmatism:
results of a 6 month prospective study. Br J Ophthalmol. 2011;95:
335–339.
17. Riau AK, Angunawela RI, Chaurasia SS, et al. Early corneal wound
healing and inflammatory responses after refractive lenticule extraction
(ReLEx). Invest Ophthalmol Vis Sci. 2011;52:6213–6221.
18. Sinha Roy A, Dupps WJ Jr, Roberts CJ. Comparison of biomechanical
effects of small-incision lenticule extraction and laser in situ keratomileusis: finite-element analysis. J Cataract Refract Surg. 2014;40:
971–980.
19. Vestergaard AH, Grauslund J, Ivarsen AR, et al. Central corneal sublayer
pachymetry and biomechanical properties after refractive femtosecond
lenticule extraction. J Refract Surg. 2014;30:102–108.
20. Kanellopoulos AJ, Asimellis G. FS200 femtosecond laser LASIK flap
digital analysis parameter evaluation: comparing two different types of
patient interface applanation cones. Clin Ophthalmol. 2013;7:
1103–1108.
21. Hatami-Marbini H, Rahimi A. Effects of bathing solution on tensile
properties of the cornea. Exp Eye Res. 2014;120:103–108.
22. Søndergaard AP, Ivarsen A, Hjortdal J. Corneal resistance to shear force
after UVA-riboflavin cross-linking. Invest Ophthalmol Vis Sci. 2013;54:
5059–5069.
23. Raiskup F, Spoerl E. Corneal crosslinking with riboflavin and ultraviolet
A. I. Principles. Ocul Surf. 2013;11:65–74.
24. Baiocchi S, Mazzotta C, Cerretani D, et al. Corneal crosslinking:
riboflavin concentration in corneal stroma exposed with and without
epithelium. J Cataract Refract Surg. 2009;35:893–899.
25. Leccisotti A, Islam T. Transepithelial corneal collagen cross-linking in
keratoconus. J Refract Surg. 2010;26:942–948.
26. Stojanovic A, Zhou W, Utheim TP. Corneal collagen cross-linking
with and without epithelial removal: a contralateral study with
0.5% hypotonic riboflavin solution. Biomed Res Int. 2014;2014:
619398.
27. Bottós KM, Schor P, Dreyfuss JL, et al. Effect of corneal epithelium on
ultraviolet-A and riboflavin absorption. Arq Bras Oftalmol. 2011;74:
348–351.
28. Kolozsvári L, Nógrádi A, Hopp B, et al. UV absorbance of the human
cornea in the 240- to 400-nm range. Invest Ophthalmol Vis Sci. 2002;43:
2165–2168.
29. Podskochy A. Protective role of corneal epithelium against ultraviolet
radiation damage. Acta Ophthalmol Scand. 2004;82:714–717.
30. Armstrong BK, Lin MP, Ford MR, et al. Biological and biomechanical responses to traditional epithelium-off and transepithelial
riboflavin-UVA CXL techniques in rabbits. J Refract Surg. 2013;
29:332–341.
31. Pinelli R, Marzouky MM, El-Shawaf HI. Tensioactive-mediated transepithelial corneal crosslinking -first laboratory report. Eur Ophthalmic
Rev. 2009;3:67–70.
32. Kocak I, Aydin A, Kaya F, et al. Comparison of transepithelial corneal
collagen crosslinking with epithelium-off crosslinking in progressive
keratoconus. J Fr Ophtalmol. 2014;37:371–376.
33. Elsheikh A, Anderson K. Comparative study of corneal strip extensometry and inflation tests. J R Soc Interf. 2005;2:177–185.
34. Sánchez P, Moutsouris K, Pandolfi A. Biomechanical and optical
behavior of human corneas before and after photorefractive keratectomy.
J Cataract Refract Surg. 2014;40:905–917.
35. Smolek MK. Interlamellar cohesive strength in the vertical meridian of
human eye bank corneas. Invest Ophthalmol Vis Sci. 1993;34:2962–2969.
Clinical Ophthalmology
36. Petsche SJ, Chernyak D, Martiz J, et al. Depth-dependent transverse
shear properties of the human corneal stroma. Invest Ophthalmol Vis Sci.
2012;53:873–880.
37. Dias J, Diakonis VF, Kankariya VP, et al. Anterior and posterior corneal
stroma elasticity after corneal collagen crosslinking treatment. Exp Eye
Res. 2013;116:58–62.
38. Kanellopoulos AJ, Asimellis G. Hyperopic correction: clinical validation
with epithelium-on and epithelium-off protocols, using variable fluence
and topographically customized collagen corneal cross-linking. Clin
Ophthalmol. 2014;8:2425–2433.
Dovepress
open access to scientific and medical research
ORIGINAL RESEARCH
Open Access Full Text Article
&RPSDULVRQRISURSK\ODFWLFKLJKHUÁXHQFH
corneal cross-linking to control, in myopic
LASIK, one year results
Anastasios John
Kanellopoulos 1,2
George Asimellis 1
Costas Karabatsas 1
LaserVision.gr Clinical and Research
Eye Institute, Athens, Greece; 2New
York University Medical School,
New York, NY, USA
1
Purpose: To compare 1-year results: safety, efficacy, refractive and keratometric stability, of
femtosecond myopic laser-assisted in situ keratomileusis (LASIK) with and without concurrent
prophylactic high-fluence cross-linking (CXL) (LASIK-CXL).
Methods: We studied a total of 155 consecutive eyes planned for LASIK myopic correction.
Group A represented 73 eyes that were treated additionally with concurrent prophylactic highfluence CXL; group B included 82 eyes subjected to the stand-alone LASIK procedure. The
following parameters were evaluated preoperatively and up to 1-year postoperatively: manifest
refractive spherical equivalent (MRSE), refractive astigmatism, visual acuity, corneal keratometry, and endothelial cell counts. We plotted keratometry measurements pre-operatively and
its change in the early, interim and later post-operative time for the two groups, as a means of
keratometric stability comparison.
Results: Group A (LASIK-CXL) had an average postoperative MRSE of 0.23, 0.19,
and 0.19 D for the 3-, 6-, and 12-month period, respectively, compared to 6.58o1.98 D preoperatively. Flat keratometry was 37.69, 37.66, and 37.67 D, compared to 43.94 D preoperatively,
and steep keratometry was 38.35, 38.36, and 38.37 D, compared to 45.17 D preoperatively.
The predictability of Manifest Refraction Spherical Equivalent (MRSE) correction showed a
correlation coefficient of 0.979. Group B (stand-alone LASIK) had an average postoperative
MRSE of 0.23, 0.20, and 0.27 D for the 3-, 6-, and 12-month period, respectively, compared
with 5.14o2.34 D preoperatively. Flat keratometry was 37.65, 37.89, and 38.02 D, compared with 43.15 D preoperatively, and steep keratometry was 38.32, 38.57, and 38.66 D,
compared with 44.07 D preoperatively. The predictability of MRSE correction showed a correlation coefficient of 0.970. The keratometric stability plots were stable for the LASIK CXL
group and slightly regressing in the standard LASIK group, a novel stability evaluation metric
that may escape routine acuity and refraction measurements.
Conclusion: Application of prophylactic CXL concurrently with myopic LASIK surgery
appears to contribute to improved refractive and keratometric stability compared to standard
LASIK. The procedure appears safe and provides a new potential for LASIK correction.
Keywords: myopic LASIK regression, femtosecond myopic LASIK, LASIK-CXL, LASIKXtra, high myopia, accelerated high-fluence collagen cross-linking
Introduction
Correspondence: A John Kanellopoulos
Laservision.gr Eye Institute, 17 Tsocha
Street, Athens, 115 21, Greece
Tel 30 210 747 2777
Fax 30 210 747 2789
Email [email protected]
7
Laser-assisted in situ keratomileusis (LASIK) is the most common form of refractive
surgery,1,2 offering predictable and stable refractive and visual outcomes.3 Specifically,
in correcting moderate to high myopia (equal or more than 6.00 D in the least-minus
meridian),4,5 there have been reports in the past indicating significant long-term
regression.6–8 The work by Alió et al9 reported that 20.8% of high myopia cases required
2373
submit your manuscript | www.dovepress.com
Clinical Ophthalmology 2014:8 2373–2381
Dovepress
© 2014 Kanellopoulos et al. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0)
License. The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further
permission from Dove Medical Press Limited, provided the work is properly attributed. Permissions beyond the scope of the License are administered by Dove Medical Press Limited. Information on
how to request permission may be found at: http://www.dovepress.com/permissions.php
http://dx.doi.org/10.2147/OPTH.S68372
Journal nam
Journal Des
Year: 2014
Volume: 8
Running he
Running he
DOI: http:/
Dovepress
Kanellopoulos et al
retreatment because of over- or undercorrection, or regression. Other studies have shown that the risk of regression
may be between 5% and 27%.10
Our team’s experience with high myopia LASIK correction suggests a slight (0.5 D) long-term postoperative
corneal steepening trend.11 This was the motivation behind
attempting to apply prophylactic in situ cross-linking (CXL)
on the stromal bed, concurrently with the LASIK procedure,
particularly in high-myopic eyes with thin residual stroma
and in younger patients who may not yet have exhibited
ectasia risk factors.12,13 The application aims to enhance
corneal rigidity and thus reduce the possibility of long-term
myopic shift.14–16
This study aimed to investigate potential differences in
safety and efficacy, as well as in the refractive and keratometric results of myopic LASIK utilizing the Wavelight®
FS200 Femtosecond Laser (Alcon Laboratories Inc, Fort
Worth, TX, USA) and the Wavelight ® EX500 Excimer
Laser (Alcon Laboratories Inc) refractive surgery platforms.
The study evaluated 1-year refractive and keratometric
results from two groups, a “LASIK-CXL” and a standalone “LASIK” group, in which no concurrent CXL was
applied.
Materials and methods
This prospective, observational, longitudinal study received
approval by the Ethics Committee of LaserVision.gr Eye
Institute and adhered to the tenets of the Declaration of
Helsinki. Informed written consent was provided and documented from each subject at the time of the first study visit.
The patients selected to receive the LASIK-CXL treatment
were comprehensively informed of the benefits and risks
involved in this procedure (which is Conformité Européene
[CE]-marked in Europe).
Inclusion and exclusion criteria
A total of 155 consecutive patients enrolled for LASIK
correction of primary myopia constituted this study. Group
A (LASIK-CXL) consisted of 73 eyes in which concurrent
prophylactic CXL was applied, while group B consisted of
82 eyes in which no such additional intervention was implemented (stand-alone LASIK). Only one eye was randomly
selected (using randomization tables) from each patient to be
included in the study, all of whom received bilateral surgery.
All operations were performed by the same surgeon (AJK).
The inclusion criteria comprised: no other previous ocular
surgery, documented refractive stability for at least 3 years,
and discontinuation of contact lens use for at least 2 weeks.
2374
Dovepress
Prior to intervention, a complete preoperative ophthalmologic
evaluation ensured there was no present or past ocular
pathology other than refractive error. The exclusion criteria
comprised: systemic or ocular diseases, eyes with history
of corneal dystrophy or herpetic eye disease, topographic
evidence of ectatic corneal disorder, epithelial warpage from
contact lens use, corneal scarring, glaucoma, severe dry eye,
and collagen vascular disease.
As per our clinical protocol for the last 6 years, in this
study, the LASIK treatments for myopia were allocated to
include LASIK-CXL if the patient had either of the following preoperative measurements: mean manifest refraction
spherical equivalent (MRSE) over 5.00 D or keratometric
astigmatism over 1.50 D on Scheimpflug-derived simulated
keratometry, or predicted residual postoperative stromal thickness less than 330 Mm. No similar restrictions were applied in
the inclusion criteria for the standard LASIK group B, other
than applying it for myopia not exceeding 10.00 D.
Surgical technique
In both groups, the FS200 Femtosecond Laser was employed
to provide a corneal flap of 110 Mm thickness and 8.00 mm
diameter.17 The average pulse energy for the flap bed cut was
0.8 MJ, the side cut angle was 70n, and the hinge position was
superior. For the bed cut, the spot and line separations were
8 Mm. For the side cut, the spot separation was 5 Mm and line
separation 3 Mm. The myopia ablation (6 mm to 6.50 mm
ablation zone diameter) treatment was accomplished with
the EX500 Excimer Laser.18
Specifically for the LASIK-CXL, after the excimer laser
ablation, and with the flap folded onto itself and protected
with a dry Wexel sponge, one drop of Vibex Rapid™ (Avedro,
Inc., Waltham, MA, USA), consisting of 0.10% saline-diluted
riboflavin (a very slightly hypotonic solution, mixed with
hydroxypropyl methylcellulose [HPMC], a dextran substitute), was placed on the exposed stromal bed afforded by the
open LASIK flap and carefully spread over the bed area with
an irrigating cannula for 60 seconds.
It is important to avoid riboflavin immersion of the flap
and its hinge – for this purpose, the flap was protected,
while remaining in a folded shape, as indicated in our earlier
work.14 The reason for this is to inhibit flap collagen CXL.
However, a small amount of riboflavin absorption, and thus
CXL, will inevitably occur as a result of osmosis during the
(however short) ultraviolet A (UVA) exposure as the flap
is in contact with the riboflavin-soaked stroma. One has to
consider the following aspects: a riboflavin-presoaked flap
will participate strongly in the UVA absorption (as it precedes
Clinical Ophthalmology 2014:8
Dovepress
the residual stroma along the illumination propagation path);
however, it will not contribute any further to the corneal
biomechanical stability and may negatively affect the postrefractive outcome, given that a 110 Mm thick flap has perhaps
only a 60 Mm stromal (collagen) content. The application of
CXL to such a thin stromal layer may lead to undesirable
flap shrinking. Regarding collateral benefits, a “CXL” flap–
stromal interface might positively affect flap adherence.19
Following stromal soaking, the flap was properly repositioned into place and the residual riboflavin-irrigated; then
a UVA fluence of 30 mW/cm2 was applied for 80 seconds
(total energy 2.4 J/cm2), provided by the KXL® CXL system
(Avedro, Inc.).
The selection of the UV irradiation parameters (fluence
and exposure time) was influenced by the following considerations: (a) provision of about half of the full “treatment”
energy in comparison with the traditional CXL protocol,
(b) minimization of UVA exposure in order to constrain
CXL within the overlaying flap, and (c) minimization of flap
dehydration and possible shrinkage.
The superficial application of UVA following the in situ
instillation of riboflavin was selected taking into account the
following aspects:
u Application of CXL to the underlying stroma increases
flap dehydration and potential predisposition for
striae.
u CXL through the repositioned flap results in some riboflavin reflux in the dehydrated flap and CXL of the inner-flap
collagen and the surface underlying the stroma. This may
increase flap–underlying stroma adherence and additionally, potentially reduce or eliminate the inadvertent space
created between them (which, in postmortem standard
LASIK histopathology, has been shown to be filled with
amorphous deposits).
u CXL has well-known disinfection, if not antimicrobial
activity; thus, conducting the CXL through a repositioned
flap reduces the chance of flap contamination by airborne microorganisms or fomites in the operating room
environment, and/or acts as an adjunct disinfectant of the
LASIK procedure.
Common to both groups, to avoid any risk of sameday accidental flap contact or rubbing, a bandage planar
soft contact lens was then placed on the ocular surface, to
be removed the following day. All patients were treated
with moxifloxacin (Vigamox; Alcon Laboratories Inc)
and 0.1% dexamethasone/chloramphenicol solution
(Dispersadron C; Alcon Laboratories Inc) at least four times
a day for 1 week.
3URSK\ODFWLFKLJKHUÁXHQFHFRUQHDOFURVVOLQNLQJLQ/$6,.
Data collection
All eyes were measured for uncorrected distance visual acuity (UDVA), best (spectacle) corrected distance visual acuity
(CDVA), and MRSE via manifest refraction and autorefraction
measurements (Speedy-i, K Model Auto Refractometer/Keratometer; Nidek, Gamagori, Japan), visual acuity (Functional
Vision Analyzer™, Stereo Optical Co, Inc., Chicago, IL, USA),
corneal topography, for steep and flat keratometry within the
3 mm radius, employing Placido topography (WaveLight®
Allegro Topolyzer™ Vario™; Alcon Laboratories Inc) and
Scheimpflug imaging (WaveLight® Oculyzer™ II Diagnostic Device; Alcon Laboratories Inc), and corneal thickness,
employing the Oculyzer II and optical coherence tomography
(OCT) (RTVue-100; Optovue, Inc, Fremont, CA, USA).20
In addition to pachymetry, OCT was employed to provide
meridional scans – the hyperreflectivity lines are considered
an indirect indication of CXL efficacy,21 as demonstrated by
our group’s study, which showed CXL demarcation lines were
evident as late as 3 years postoperatively.22 An example of an
OCT meridional image scan of a treated cornea is provided in
Figure 1 and shows an increased reflectivity of the upper stromal
bed. This is supportive of our argument that CXL mainly affects
the underlying stroma and not the superjacent flap.
The postoperative evaluation additionally included slitlamp examination, clinical evaluation of dry eye, indications
of epithelial ingrowth,23 and corneal haze. In addition, we
measured endothelial cell counts preoperatively and 1-month
postoperatively, employing noncontact specular microscopy
(FA-3709; Konan Medical, Irvine, CA, USA).
Postoperative examinations were conducted at 1 day,
1 week, 3 months, 6 months, and up to 1 year. This report
presents the refractive and keratometric data analysis from
the 1-year follow-up visits. Data were processed using
web-based ophthalmic outcome analysis software (IBRA;
Zubisoft GmbH, Oberhasli, Switzerland).24 Descriptive
statistics and analysis were performed using Minitab ®
Figure 1 Anterior-segment optical coherency high-resolution cross-sectional
(6 mm) image of an eye treated with LASIK-CXL for 2.25 D of sphere and 0.25 D
of astigmatism, obtained 1-year postoperatively. Blue arrows indicate the LASIK
ÁDSZKLOH\HOORZDUURZVLQGLFDWHWKHVWURPDOK\SHUUHÁHFWLRQOLQHZKLFKFRUUHODWHV
with the depth of the prophylactic cross-linking effect.
Abbreviations: CXL, cross-linking; LASIK, laser-assisted in situ keratomileusis.
Dovepress
2375
UDVA outcome and stability
The monocular UDVA outcome (Figure 2) indicates
that in the LASIK-CXL group-A, 90.4% of the eyes had
Refractive predictability and accuracy
The predictability results are presented in the form of
linear regression scatterplots (Figure 4), in which the
vertical axis corresponds to the achieved MRSE, and the
horizontal axis corresponds to the attempted MRSE. The
data for the LASIK-CXL group had a coefficient of determination (r2) of 0.979, while for the stand-alone group-B,
this was 0.970.
The postoperative MRSE refraction results are presented,
within 0.50 D intervals, in Figure 5. In the LASIK-CXL
group, MRSE refraction between 0.50 and 0.00 D was
achieved in 82.2% of the eyes, and in the stand-alone group,
this was achieved in 81.7% (no statistically significant difference [P0.079]).
Postoperative refractive astigmatism results, within
intervals of 0.50 D representing the accuracy of the cylinder
correction, are illustrated in Figure 6. The LASIK-CXL
group had a mean preoperative cylinder of 0.93o0.04 D,
while the stand-alone LASIK group had a mean preoperative
Table 1 Preoperative demographics, including the planned residual stromal thickness, between the two groups
Group A (LASIK-CXL): 65 eyes
Age (years)
Mean
Std dev
Min
Max
27.5
o6.1
19
39
Pre-op
CCT (*m)
545.96
o33.93
474
595
Planned
residual (*m)
329.22
o32.15
299
398
Group B (stand-alone LASIK): 75 eyes
Post-op
CCT (*m)
438.11
o28.35
414
506
Age
(years)
24.2
o5.8
18
42
Pre-op
CCT (*m)
553.51
o19.11
503
592
Planned
residual (*m)
344.34
o20.55
313
408
Post-op
CCT (*m)
452.25
o21.18
423
510
LASIK-CXL group A
90.4%
73 eyes (plano target)
100.0%
98.6%
74.0%
70%
Post-op UDVA
60%
Pre-op CDVA
50%
41.1%
40%
30%
20%
12.3%
10%
0%
82 eyes (plano target)
20/12.5
20/16
20/20
20/25
20/32
89.0%
85.4%
85.4%
12-months post-op
80%
100.0%
98.8%
95.1%
95.1%
69.5%
70%
Post-op UDVA
60%
Pre-op CDVA
50%
40%
30%
26.8%
20%
11.0%
0.0% 0.0%
0%
20/12.5
20/40
Cumulative Snellen visual acuity
20/x or better
20/16
20/20
20/25
20/32
20/40
Cumulative Snellen visual acuity
20/x or better
Figure 2 Postoperative uncorrected distance visual acuity (blue columns) versus preoperative corrected distance visual acuity (red columns) 1-year postoperatively,
in (A) the LASIK-CXL group and (B) the stand-alone LASIK group.
Abbreviations: CDVA, corrected distance visual acuity; CXL, cross-linking; LASIK, laser-assisted in situ keratomileusis; UDVA, uncorrected distance visual acuity.
cylinder of 0.82o0.03 D. The LASIK-CXL group had,
postoperatively, 90.4% of eyes with less than 0.25 D of
refractive astigmatism, and mean cylinder of 0.16o0.04 D.
The stand-alone LASIK group had 91.5% with less than
0.25 D of refractive astigmatism, and mean cylinder of
0.15o0.04 D.
Refractive and keratometric stability
Refractive stability was demonstrated by the MRSE correction, as followed during the 1-, 3-, 6-, and 12-month
postoperative visits (Figure 7). The 1-year mean postoperative MRSE was 0.19o0.17 D in the LASIK-CXL group
and 0.27o0.23 D in the stand-alone LASIK group. These
findings indicate a reduced refractive shift in the LASIK-CXL
group in comparison with the stand-alone group (P0.063).
The keratometric stability, demonstrated by the K-flat and
60%
56.2%
12-months post-op
50%
56.1%
LASIK-CXL group A, 73 eyes (%)
Stand-alone LASIK group B, 82 eyes (%)
40%
37.8%
35.6%
30%
20%
10%
0%
6.8%
1.2%
3.7%
1.4% 1.2%
0.0% 0.0%
0.0% 0.0%
0.0%
Lost 3 or
more
Lost 2
Lost 1 Unchanged Gained 1 Gained 2 Gained 3 or
more
Change in Snellen lines of CDVA
2376
Group B stand-alone LASIK
90%
10%
Figure 3 Change in corrected visual acuity, as a percentage of eyes with gain/loss in
Snellen lines of corrected distance visual acuity 1-year postoperatively.
Abbreviations: CDVA, corrected distance visual acuity; CXL, cross-linking; LASIK,
laser-assisted in situ keratomileusis.
Dovepress
100%
0.0% 0.0%
Notes: CCT and planned residual stroma were reported in Mm. Post-op results refer to the 1-year results.
Abbreviations: CCT, Central corneal thickness; CXL, cross-linking; LASIK, laser-assisted in situ keratomileusis; Max, maximum; Min, minimum; Std dev, standard deviation.
B
86.3%
12-months post-op
80%
97.3%
95.9%
94.5%
Cumulative % of eyes
90%
(IÀFDF\RI&'9$
The gain–loss data (preoperative CDVA versus postoperative
UDVA) (Figure 3) indicate that in the LASIK-CXL group,
35.6% of the eyes were unchanged, 56.2% gained one Snellen
line, and 8.2% (six eyes) gained two or more Snellen lines.
No eye lost any line. In the stand-alone LASIK group, 37.8%
of the eyes were unchanged, 56.1% gained one Snellen line,
and 4.9% (four eyes) gained two or more lines. Only 1.2%
(one eye) lost one line.
100%
K-steep average values up to the 1-year postoperative visit,
is illustrated in Figure 8. The results indicate an increased
keratometric stability in the LASIK-CXL group (1-year
at 0.03 D in the flat and 0.05 D in the steep compared
A
Achieved spherical equivalent
refraction (D)
The 73 eyes included in group A (LASIK-CXL) belonged
to 42 female and 31 male patients; of these, 36 eyes were
right (OD) and 37 left (OS). The mean patient age at the time
of operation was 27.1o6.0 (range: 19 to 39) years. Preoperatively, the mean refractive error was sphere 6.62o2.12
(range: 2.50 to 11.50) D, cylinder 0.98o0.15 (range: 0.00
to 5.00) D, and the MRSE was 6.58o1.98 (range: 2.50
to 11.50) D. Mean preoperative central corneal thickness
was 545.96o33.93 (range: 474 to 595) Mm and at 1-year postoperatively, was 438.11o28.35 (range: 414 to 506) Mm.
The 82 eyes in group B (stand-alone LASIK) belonged
to 41 female and 41 male patients; 41 eyes were right (OD)
and 41 left (OS). Mean patient age at the time of surgery was
24.9o5.9 (range: 18 to 42) years. Preoperatively, mean refractive error was sphere 5.05o1.74 (range: 2.50 to 9.50) D,
cylinder 0.85o0.13 (range: 0.00 to 4.50) D, and MRSE
5.14o2.34 (range: 2.50 to 9.50) D. Mean preoperative
central corneal thickness was 553.51o19.11 (range: 503 to
592) Mm, and 1-year postoperatively, was 452.25o21.18
(range: 423 to 510) Mm.
Demographic and corneal thickness results are also
reported in Table 1. No adverse events, including epithelial
ingrowth, diffuse lamellar keratitis, postoperative haze, or
other complications, were detected in either of the groups.
Endothelial cell counts were not statistically different in
either group, when compared preoperatively and 1-month
postoperatively.
A
–12
Group A LASIK-CXL 73 eyes, 1-year post-op
–11
Achieved (D) =0.0113+1.011 attempted (D)
–10
–9
–8
–7
–6
Regression
95% CI
95% PI
–5
–4
S
R-Sq
R-Sq (adj)
–3
–2
–2
–3
–4
–5
–6
–7
–8
–9
0.313741
97.9%
97.9%
–11
–10
–12
Attempted spherical equivalent refraction (D)
B
Achieved spherical equivalent
refraction (D)
Results
postoperative UDVA 20/20 (1.0 decimal) or better, and
94.5% had 20/25 (0.8 decimal) or better. In the stand-alone
LASIK group, 85.4% of the eyes had postoperative UDVA
better than 20/20 (1.0 decimal), and 89.0% had better than
20/25 (0.8 decimal). The differences between the two groups
at the 20/20 and the 20/25 levels were statistically significant
(P0.042 and P0.037, respectively).
% of eyes
16.2.3 Statistical Software (Minitab Ltd., Coventry, UK) and
Origin Lab 9 (OriginLab Corp, Northampton, MA, USA).
P-values less than 0.05 were indicative of statistically significant results in this study.
Dovepress
Cumulative % of eyes
Dovepress
Kanellopoulos et al
–12
Group B LASIK stand-alone 82 eyes, 1-year post-op
–11
Achieved (D) =–0.1337+1.030 attempted (D)
–10
–9
–8
–7
–6
Regression
95% CI
95% PI
–5
–4
S
0.315772
R-Sq
97.0%
R-Sq (adj) 97.0%
–3
–2
–2
–3
–4
–5
–6
–7
–8
–9
–10
–11
–12
Attempted spherical equivalent refraction (D)
Figure 4 Predictability of spherical equivalent correction, measured at 1-year
postoperatively, showing achieved spherical equivalent (vertical axis) versus
attempted spherical equivalent (horizontal axis), in (A) the LASIK-CXL group and
(B) the stand-alone LASIK group.
Abbreviations: CDVA, FRUUHFWHG GLVWDQFH YLVXDO DFXLW\ &, FRQÀGHQFH LQWHUYDO
&;/FURVVOLQNLQJ3,SUHGLFWLRQLQWHUYDO6VXPRIUHVLGXDOV5VTFRHIÀFLHQWRI
GHWHUPLQDWLRQ5VTDGMDGMXVWHGFRHIÀFLHQWRIGHWHUPLQDWLRQ
Dovepress
2377
% of eyes
70%
12-months post-op
LASIK-CXL group A, 73 eyes
60%
Stand-alone LASIK group B, 82 eyes
50%
40%
30%
20%
10%
0%
6.8%
0.0% 0.0%
9.6%
8.5%
7.3%
0.0% 1.2%
–2.00 to
1.01
<–2.00
–1.00 to
–0.51
–0.50 to
0.00
0.00 to
+0.50
1.4% 1.2%
0.0% 0.0%
+0.50 to
+1.00
>1.00
Postoperative spherical equivalent
refraction (D)
Figure 5 Postoperative spherical equivalent refraction for both groups, 1-year
postoperatively.
with the 1-month baseline) compared with the stand-alone
LASIK group (0.67 D and 0.55 D, respectively), which
was statistically significant (P0.039).
Discussion
Improved diagnostics, ablation profiles, and laser-beam
tracking refinements of the LASIK procedure, 25 and
improvements attributed to femtosecond laser-assisted flap
creation26–28 all have contributed to an excellent track record
in myopia correction.
However, refractive regression in high myopic corrections, remains a possibility. There are several possible
mechanisms leading to post-LASIK regression. For example,
a correlation between increased epithelial thickness and
myopia correction up to 1-year postoperatively was noted, in
a study by Spadea et al29 in high-myopic (myopias between
8.50 and 12.25 D) patients. This epithelial thickening in
A
B
#!"#%'
#!&"($
! %$"!$%
!"
!$%
!"
! %$
%!
%!
%!
%!
%!
%!
%!
Refractive astigmatism (D)
"# #"
'
–2
–3
–4
#
#
#
#
#
#
#
(
Refractive astigmatism (D)
Group A, LASIK-CXL, 65 eyes
Group B, stand-alone LASIK, 75 eyes
–5
–6
–7
1
3
6
Months following surgery
12
Figure 7 Stability of manifest spherical equivalent refraction for both groups,
expressed in diopters (D), up to 1-year postoperatively.
Abbreviations: CXL, cross-linking; LASIK, laser-assisted in situ keratomileusis; SD,
standard deviation.
Comparison of the stability results between the two
groups indicates that in the stand-alone group, there was a
slight positive slope in the keratometric readings, both at
the flat and the steep meridian, as illustrated in Figure 8,
which is suggestive of a mild progressive corneal steepening. The recorded changes correspond to 0.67 D for the
flat meridian and 0.54 D for the steep meridian. The data
clearly show a trend toward mild corneal steepening in
the long-term postoperative period. A similar refractive
shift has been reported previously by our team in LASIK
corrections of high myopia with no prophylactic CXL
application.11
There was no such trend of keratometric shift in the
LASIK-CXL group (0.03 D and 0.05 respectively).
Other differences between the two groups were the slightly
increased stability of the MRSE (Figure 7), as well as the
improved predictability (Figure 4), despite the larger range of
attempted correction and increased preoperative astigmatism
LASIK-CXL group,
65 eyes up to 12-months post-op
45
43
41
39
37
35
(Figure 6). It is worth noting that the mean spherical error
(S), as well as cylinder error (C) treated in group A (mean S
6.62 D, maximum S 11.50 D; mean C 1.35 D, maximum
C 5.25 D) was significantly greater than in the LASIK standalone group (mean S 5.05 D, maximum S 9.50 D; mean
C 0.85 D, maximum C 3.50 D). Despite the apparently
more challenging cases included in group A (LASIK-CXL)
compared to group B (Standard-LASIK), the refractive
results in the LASIK-CXL group were equally good and, in
some cases, slightly better.
One aspect that needs consideration is the possibility
of refractive flattening as a result of the CXL applied. Our
clinical experience, as well as the peer-review literature,
suggests the continued progression of the CXL effect over
time.33 We have indicated that the long-term keratometry
flattening progression in the fully cross-linked corneas is of
the order of 0.30 D. One has to acknowledge the following
two parameters that differentiate this finding, when considering the LASIK-CXL:
u The keratoconus management cases were fundamentally
unstable ectatic corneas, whereas in the present work only
healthy corneas were included, and
u The keratoconus management cases received the “full
energy” treatment (up to 6 J/cm2), whereas in the present work, the LASIK-CXL eyes received only a “partial
energy” treatment (2.4 J/cm2), corresponding to less than
half of the standard protocol energy.
It may thus be estimated that the possibility of long-term
keratometric flattening may well be restricted. Additional
long-term studies are required to investigate this aspect.
In view of the expressed skepticism by colleagues regarding possible regression of the refractive effect,34 sometimes,
despite low preoperative risk (for example, classified as low
B
47
! !#%
#!$ &"#" "#
–1
A
% of eyes
% of eyes
high myopia has been corroborated recently in femtosecond
LASIK correction of high myopia.30 Furthermore, a comparison of stand-alone LASIK to LASIK-CXL in high myopia
verified that the observed post-LASIK epithelial thickening
changes are significantly less prominent in LASIK-CXL
cases. This difference may correlate with higher regression
rates and/or may depict increased biomechanical instability
in stand-alone LASIK.31 We believe that this finding is a
manifestation of the same aspect, which is the chief difference
between the two groups – the application of preventive CXL
in this group. As we have previously demonstrated,32 CXL
affects epithelial thickness, leading to reduced overall
thickness.
In the present study, we investigated up to 1-year postoperative refractive and stability results of 155 eyes subjected
to femtosecond-laser LASIK for myopia between two
groups – group A in which prophylactic high-fluence CXL
was incorporated and group B that received stand-alone
LASIK. The two groups in the study were by all other
means matched: ablation zone, flap thickness, surgeon, lasers
employed, and postoperative medication and treatment. Our
research on this subject matter is ongoing, and we do hope
to report long-term follow-up results in the future.
The postoperative evaluation in the LASIK-CXL group
did not indicate clinical or topographic evidence of complications in comparison with the stand-alone group. Visual rehabilitation between the two groups, as expressed by CDVA
and contrast sensitivity evaluation, was at similar levels,
without induction of side effects or compromise of visual
safety. The refractive outcome, predictability, and stability
were completely satisfactory, and in some cases superior to
standard LASIK (for example, data shown in in Figure 2,
subgroup of achieved visual acuity of 20/16).
0
Time after surgery (months)
Keratometric readings (D)
82.2% 81.7%
80%
Dovepress
Keratometric readings (D)
90%
Mean ' SD spherical equivalent
refraction (D)
Dovepress
Kanellopoulos et al
47
Stand-alone LASIK group,
75 eyes up to 12-months post-op
45
43
41
39
37
Time after surgery (months)
35
Preoperative
1-month
3-months
6-months
12-months
Preoperative
1-month
3-months
6-months
12-months
K-flat
43.94
37.64
37.69
37.66
37.67
K-flat
43.15
37.45
37.65
37.89
38.02
K-steep
45.17
38.32
38.35
38.36
38.37
K-steep
44.07
38.12
38.32
38.57
38.66
Figure 6 Refractive astigmatism preoperatively (red columns) and 1-year postoperatively (blue columns), in (A) the LASIK-CXL group and (B) the stand-alone LASIK
group.
Notes: The graph shows percentage of eyes (vertical axis) versus refractive astigmatism (horizontal axis).
Figure 8 Stability of corneal keratometry for (A) the LASIK-CXL group and (B) the stand-alone LASIK group, expressed in diopters (D), up to 1-year postoperatively.
2378
Dovepress
Dovepress
2379
Dovepress
Kanellopoulos et al
risk in the Ectasia Risk Score System), caution has been
recommended when LASIK was performed in cases of high
myopia with a thin residual stromal bed.36
Our team has performed and reported a large number of
successful LASIK-CXL procedures over the last 8 years, and
we view this prophylactic treatment as a pivotal biomechanical enhancement of the LASIK procedure – in a young adult,
in any patient under the age of 30 years with high myopia
and/or astigmatism, and any patient with a difference of
over 0.50 D in the amount of the astigmatism between the
two eyes. In our opinion, it does not merit “leniency” with
preoperative form-fruste keratoconus criteria. All cases studied in this work, as well as in previous reports by our group,
have been screened thoroughly for any signs of tomographic
cornea irregularity.
35
Conclusion
LASIK combined with a prophylactic CXL intervention
appears to provide predictability as well as refractive and
keratometric stability. The data reported in this study provide
evidence of the safety and efficacy of this approach. The adjuvant CXL procedure adds enhanced corneal biomechanical
stability. High-myopic and younger age LASIK cases, may
require biomechanical re-enforcement, as means of reducing
the incidence and degree of future myopic regression and/or
the potential ectasia risk.
Author contributions
AJK design and conduct of the study, and collection and
interpretation of the data. AJK performed data management, and CK and GA analyzed the data. AJK, CK and GA
prepared the manuscript and AJK, CK, and GA participated
in manuscript review. All authors provided manuscript
approval.
Disclosure
AJK has held consultant or advisory positions with Alcon/
WaveLight, Allergan, Avedro, and i-Optics. The other
authors report no other conflicts of interest in this work.
References
1. Solomon KD, Fernández de Castro LE, Sandoval HP, et al; Joint LASIK
Study Task Force. LASIK world literature review: quality of life and
patient satisfaction. Ophthalmology. 2009;116(4):691–701.
2. Shortt AJ, Allan BD, Evans JR. Laser-assisted in-situ keratomileusis
(LASIK) versus photorefractive keratectomy (PRK) for myopia.
Cochrane Database Syst Rev. 2013;1:CD005135.
3. Shortt AJ, Bunce C, Allan BD. Evidence for superior efficacy and safety
of LASIK over photorefractive keratectomy for correction of myopia.
Ophthalmology. 2006;113(11):1897–1908.
2380
Dovepress
4. Liu Z, Li Y, Cheng Z, Zhou F, Jiang H, Li J. Seven-year follow-up of
LASIK for moderate to severe myopia. J Refract Surg. 2008;24(9):
935–940.
5. Güell JL, Muller A. Laser in situ keratomileusis (LASIK) for myopia
from 7 to 18 diopters. J Refract Surg. 1996;12(2):222–228.
6. Oruço÷lu F, Kingham JD, Kendüúim M, Ayo÷lu B, Toksu B, Göker S.
Laser in situ keratomileusis application for myopia over minus 14 diopter
with long-term follow-up. Int Ophthalmol. 2012;32(5):435–441.
7. Magallanes R, Shah S, Zadok D, et al. Stability after laser in situ
keratomileusis in moderately and extremely myopic eyes. J Cataract
Refract Surg. 2001;27(7):1007–1012.
8. Chayet AS, Assil KK, Montes M, Espinosa-Lagana M, Castellanos A,
Tsioulias G. Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia. Ophthalmology. 1998;105(7):
1194–1199.
9. Alió JL, Muftuoglu O, Ortiz D, et al. Ten-year follow-up of laser in
situ keratomileusis for myopia of up to 10 diopters. Am J Ophthalmol.
2008;145(1):46–54.
10. Chen YI, Chien KL, Wang IJ, et al. An interval-censored model for
predicting myopic regression after laser in situ keratomileusis. Invest
Ophthalmol Vis Sci. 2007;48(8):3516–3523.
11. Kanellopoulos AJ, Asimellis G. Refractive and keratometric stability
in high myopic LASIK with high-frequency femtosecond and excimer
lasers. J Refract Surg. 2013;29(12):832–837.
12. Binder PS. Analysis of ectasia after laser in situ keratomileusis: risk
factors. J Cataract Refract Surg. 2007;33(9):1530–1538.
13. Randleman JB. Post-laser in-situ keratomileusis ectasia: current
understanding and future directions. Curr Opin Ophthalmol. 2006;
17(4):406–412.
14. Kanellopoulos AJ. Long-term safety and efficacy follow-up of prophylactic higher fluence collagen cross-linking in high myopic laser-assisted
in situ keratomileusis. Clin Ophthalmol. 2012;6:1125–1130.
15. Celik HU, Alagöz N, Yildirim Y, et al. Accelerated corneal crosslinking
concurrent with laser in situ keratomileusis. J Cataract Refract Surg.
2012;38(8):1424–1431.
16. Kanellopoulos AJ, Pamel GJ. Review of current indications for
combined very high fluence collagen cross-linking and laser in situ
keratomileusis surgery. Indian J Ophthalmol. 2013;61(8):430–432.
17. Kanellopoulos AJ, Asimellis G. Digital analysis of flap parameter
accuracy and objective assessment of opaque bubble layer in femtosecond laser-assisted LASIK: a novel technique. Clin Ophthalmol. 2013;
7:343–351.
18. Kanellopoulos AJ, Asimellis G. Long-term bladeless LASIK outcomes
with the FS200 Femtosecond and EX500 Excimer Laser workstation:
the Refractive Suite. Clin Ophthalmol. 2013;7:261–269.
19. Mi S, Dooley EP, Albon J, Boulton ME, Meek KM, Kamma-Lorger CS.
Adhesion of laser in situ keratomileusis-like flaps in the cornea: Effects
of crosslinking, stromal fibroblasts, and cytokine treatment. J Cataract
Refract Surg. 2011;37(1):166–172.
20. Kanellopoulos AJ, Asimellis G. Comparison of high-resolution
Scheimpflug and high-frequency ultrasound biomicroscopy to anteriorsegment OCT corneal thickness measurements. Clin Ophthalmol. 2013;
7:2239–2247.
21. Seiler T, Hafezi F. Corneal cross-linking-induced stromal demarcation
line. Cornea. 2006;25(9):1057–1059.
22. Kanellopoulos AJ, Asimellis G. Introduction of quantitative and qualitative cornea optical coherence tomography findings induced by collagen
cross-linking for keratoconus: a novel effect measurement benchmark.
Clin Ophthalmol. 2013;7:329–335.
23. Henry CR, Canto AP, Galor A, Vaddavalli PK, Culbertson WW,
Yoo SH. Epithelial ingrowth after LASIK: clinical characteristics, risk
factors, and visual outcomes in patients requiring flap lift. J Refract
Surg. 2012;28(7):488–492.
24. Zuberbuhler B, Galloway P, Reddy A, Saldana M, Gale R. A webbased information system for management and analysis of patient
data after refractive eye surgery. Comput Methods Programs Biomed.
2007;88(3):210–216.
Dovepress
25. Maldonado MJ, Nieto JC, Piñero DP. Advances in technologies for
laser-assisted in situ keratomileusis (LASIK) surgery. Expert Rev Med
Devices. 2008;5(2):209–229.
26. Vestergaard A, Ivarsen A, Asp S, Hjortdal JØ. Femtosecond (FS) laser
vision correction procedure for moderate to high myopia: a prospective
study of ReLEx(®) flex and comparison with a retrospective study of FSlaser in situ keratomileusis. Acta Ophthalmol. 2013;91(4):355–362.
27. Kymionis GD, Kankariya VP, Plaka AD, Reinstein DZ. Femtosecond
laser technology in corneal refractive surgery: a review. J Refract Surg.
2012;28(12):912–920.
28. Kanellopoulos AJ, Asimellis G. Three-dimensional LASIK flap
thickness variability: topographic central, paracentral and peripheral
assessment, in flaps created by a mechanical microkeratome (M2) and
two different femtosecond lasers (FS60 and FS200). Clin Ophthalmol.
2013;7:675–683.
29. Spadea L, Fasciani R, Necozione S, Balestrazzi E. Role of the corneal
epithelium in refractive changes following laser in situ keratomileusis
for high myopia. J Refract Surg. 2000;16(2):133–139.
30. Kanellopoulos AJ, Asimellis G. Longitudinal postoperative LASIK
epithelial thickness profile changes in correlation with degree of myopia
correction. J Refract Surg. 2014;30(3):166–171.
31. Kanellopoulos AJ, Asimellis G. Epithelial remodeling after femtosecond
laser-assisted high myopic LASIK: comparison of stand-alone with
LASIK combined with prophylactic high-fluence cross-linking. Cornea.
2014;33(5):463–469.
Publish your work in this journal
Clinical Ophthalmology is an international, peer-reviewed journal
covering all subspecialties within ophthalmology. Key topics include:
Optometry; Visual science; Pharmacology and drug therapy in eye
diseases; Basic Sciences; Primary and Secondary eye care; Patient
Safety and Quality of Care Improvements. This journal is indexed on
32. Kanellopoulos AJ, Aslanides IM, Asimellis G. Correlation between
epithelial thickness in normal corneas, untreated ectatic corneas, and
ectatic corneas previously treated with CXL; is overall epithelial
thickness a very early ectasia prognostic factor? Clin Ophthalmol.
2012;6:789–800.
33. Kanellopoulos AJ, Asimellis G. Keratoconus management: longterm stability of topography-guided normalization combined with
high-fluence CXL stabilization (the Athens Protocol). J Refract Surg.
2014;30(2):88–93.
34. Ambrósio R, Dawson DG, Salomão M, Guerra FP, Caiado AL,
Belin MW. Corneal ectasia after LASIK despite low preoperative risk:
tomographic and biomechanical findings in the unoperated, stable,
fellow eye. J Refract Surg. 2010;26(11):906–911.
35. Randleman JB, Trattler WB, Stulting RD. Validation of the Ectasia Risk
Score System for preoperative laser in situ keratomileusis screening.
Am J Ophthalmol. 2008;145(5):813–818.
36. Spadea L, Cantera E, Cortes M, Conocchia NE, Stewart CW. Corneal
ectasia after myopic laser in situ keratomileusis: a long-term study. Clin
Ophthalmol. 2012;6:1801–1813.
Dovepress
PubMed Central and CAS, and is the official journal of The Society of
Clinical Ophthalmology (SCO). The manuscript management system
is completely online and includes a very quick and fair peer-review
system, which is all easy to use. Visit http://www.dovepress.com/
testimonials.php to read real quotes from published authors.
Submit your manuscript here: http://www.dovepress.com/clinical-ophthalmology-journal
Dovepress
2381
ARTICLE
1598
Epithelial remodeling after partial
topography-guided normalization
and high-fluence short-duration crosslinking
(Athens protocol): Results up to 1 year
recent availability of in vivo, 3-dimensional (3-D)
corneal epithelial mapping by AS-OCT in clinical practice7 allows easy capture of optical images and highspeed measurements conferred by Fourier-domain
signal processing.8,9
This study used this new clinical modality to evaluate the longitudinal postoperative changes in epithelial thickness distribution as well as the epithelial layer
topographic variability in a large group of keratoconic
cases treated using the Athens protocol. The results in
these eyes were compared with those in untreated keratoconic eyes and in healthy control eyes.
Anastasios John Kanellopoulos, MD, George Asimellis, PhD
PURPOSE: To compare epithelial remodeling in keratoconic eyes that had photorefractive keratectomy and corneal collagen crosslinking (Athens protocol) with that in untreated keratoconic eyes
and healthy eyes.
PATIENTS AND METHODS
This observational comparative prospective study received
approval by the Ethics Committee, LaserVision.gr Institute,
and adhered to the tenets of the Declaration of Helsinki.
All patients provided informed written consent at the time
of the first clinical visit. Exclusion criteria were systemic
disease, previous corneal surgery, history of chemical injury
or delayed epithelial healing, and pregnancy or lactation.
SETTING: Private clinical practice, Athens, Greece.
DESIGN: Comparative case series.
METHODS: Fourier-domain anterior segment optical coherence tomography (AS-OCT) was used to
obtain in vivo 3-dimensional epithelial thickness maps and center, superior, inferior, maximum,
minimum, mean, midperipheral, and variability data.
Patient Enrollment and Surgical Technique
Group A In Group A, eyes were treated for keratoconus
RESULTS: Group A comprised 175 treated keratoconic eyes (Athens protocol); Group B, 193 untreated keratoconic eyes; and Group C, 160 healthy eyes. The 1-year mean center epithelial
thickness in Group A was 47.78 mm G 7.36 (SD) (range 33 to 64 mm). At the first clinical visit,
it was 52.09 G 6.80 mm (range 36 to 72 mm) in Group B and 52.54 G 3.23 mm (range 45 to
59 mm) in Group C. The mean thickness range in Group A at 1 year was !19.94 G 7.21 mm
(range !6 to !34 mm). It was !21.83 G 12.07 mm (range !4 to !66 mm) in Group B and
!6.86 G 3.33 mm (range !3 to !29 mm) in Group C. The mean topographic thickness variability
in Group A at 1 year was 4.64 G 1.63 mm (range 1.6 to 8.1 mm) (P<.05). It was 5.77 G 3.39 mm
(range 1.3 to 17.8 mm) in Group B and 1.59 G 0.79 mm (range 0.6 to 5.6 mm) in Group C.
with the Athens protocol. All procedures were performed
by the same surgeon (A.J.K.) using an EX500 excimer laser10
(Alcon Surgical, Inc.) with topography-guided custom
partial ablation. Figure 1 shows an example of treatment
planning, the distribution of the ablation depth, a preoperative axial curvature map, a postoperative axial curvature
map, and the difference in axial curvature map between
preoperatively and postoperatively. Immediately after surface normalization, accelerated CXL was applied using the
KXL System (Avedro, Inc.). The patients were followed for
up to 1 year.
CONCLUSION: Anterior segment OCT indicated a thinner and more homogeneous remodeled
epithelium in the keratoconic eyes treated using the Athens protocol.
Group B Group B comprised eyes with keratoconus that
Financial Disclosure: Dr. Kanellopoulos is a consultant to Alcon Surgical, Inc.; Wavelight Laser
Technologie AG; Avedro, Inc.; and i-Optics Optikger€ate GmbH. Dr. Asimellis has no financial or proprietary interest in any material or method mentioned.
had not received surgical treatment. Inclusion criteria were
a clinical diagnosis of progressive keratoconus (confirmed
by a complete ophthalmologic evaluation), minimum age
17 years, and corneal thickness of at least 300 mm. The keratoconus diagnosis was further confirmed using the Wavelight Oculyzer II (Alcon Surgical, Inc.) and the Pentacam
high-resolution Scheimpflug imaging camera11 (Oculus
Optikger€ate GmbH).
J Cataract Refract Surg 2014; 40:1597–1602 Q 2014 ASCRS and ESCRS
We previously reported overall reduced corneal
epithelial thickness in keratoconic eyes that were
treated with (1) excimer laser debridement of the top
50 mm of the epithelium, (2) partial topographyguided excimer ablation, and (3) immediate highfluence ultraviolet-A radiation (10 mW/cm2) and
short-duration (10 minutes) corneal collagen crosslinking (CXL) with riboflavin in a procedure known as the
Athens protocol.1–3 Our goal was to arrest the keratectasia progression4 and provide a less irregular anterior
corneal surface. In l study,1 which was performed using
high-frequency scanning ultrasound biomicroscopy
Q 2014 ASCRS and ESCRS
Published by Elsevier Inc.
(UBM), the epithelial thickness in a group of untreated
keratoconic eyes was compared with that in a
group of keratoconic eyes treated using the Athens
protocol.
Epithelial thickness assessment has been facilitated
by the development of anterior segment optical coherence tomography (AS-OCT).5 Although there are
studies of AS-OCT epithelium measurement in the
peer-reviewed literature, until recently and to our
knowledge, the methodology and instrumentation
mainly used an on-screen caliper tool6; thus, only local
point–thickness measurements were reported. The
0886-3350/$ - see front matter
http://dx.doi.org/10.1016/j.jcrs.2014.02.036
EPITHELIAL REMODELING IN KERATOCONIC EYES
1597
Submitted: November 11, 2013.
Final revision submitted: February 4, 2014.
Accepted: February 5, 2014.
From Laservision.gr Eye Institute (Kanellopoulos), Athens, Greece,
and the New York University Medical School (Kanellopoulos,
Asimellis), New York, New York, USA.
Corresponding author: Anastasios John Kanellopoulos, MD,
Laservision.gr Clinical and Research Institute, 17 Tsocha Street,
Athens, Greece, Postal Code: 115 21. E-mail: ajk@brilliantvision.
com.
Figure 1. A: Preoperative tomographic (anterior corneal instantaneous [tangential]) map obtained via Scheimpflug imaging. Keratometric power reported in diopters. B: Corresponding postoperative
map. C: Treatment planning showing ablation depth (in mm) and
topographic distribution obtained via the refractive platform software. D: Difference between postoperative sagittal curvature map
(B) and preoperative sagittal curvature map (A) (N Z nasal; T Z
temporal).
Group C Group C, the control group, comprised unoper-
ated normal eyes with no current or past ocular pathology
other than refractive error and no present irritation or dryeye disorder, all of which were confirmed during a complete
ophthalmologic evaluation. Contact lens wearers were
excluded from this group.
Imaging Instrumentation
The RTVue-100 Fourier-domain AS-OCT system (Optovue, Inc.), running on analysis and report software version
A6 (9.0.27), was used in the study. Data output included total
corneal and epithelial thickness maps corresponding to a
6.0 mm diameter area. In all cases, to avoid potential artifacts
(eg, due to eyedrop instillation), OCT imaging preceded the
ocular clinical examination and was performed by the same
trained investigator. The settings were as follows: L-Cam
lens and 8 radial meridional B-scans per acquisition consisting of 1024 A-scans each with a 5 mm axial resolution. These 8
radial meridional scans, all acquired in less than 0.5 second,
were used by the system software to produce by interpolation 3-D thickness maps. Images with quality greater than
30, determined using the signal strength index parameter,
were considered in the study. The signal strength index
parameter measures the average signal strength across the
scan. Two consecutive individual acquisitions were obtained
in each case (eye) to ensure data validity; the mean value of 2
was used in this study.
Data Collection and Statistical Analysis
In Group A, the postoperative measurements were performed at 1 and 6 months as well as at 1 year. Imaging in
J CATARACT REFRACT SURG - VOL 40, OCTOBER 2014
Figure 2. Comparative AS-OCT epithelial thickness (mm) 3-D maps
shows an image from Group A taken 1 year postoperatively and
an image from Group B (I Z inferior; IN Z inferior–nasal; IT Z inferior–temporal; N Z nasal; S Z superior; SN Z superior–nasal; ST Z
superior–temporal; T Z temporal).
Group B and Group C was performed during the first clinical
visit.
The main analysis report produced by the AS-OCT system
displayed total corneal (reported as pachymetry) and epithelial 3-D thickness maps covering the 6.0 mm diameter area.
Corneal pachymetry was assessed by the central corneal
thickness (CCT) and minimum corneal thickness. Epithelial
thickness assessment comprised the following measurements: pupil center, superior, inferior, minimum, maximum,
mean, peripheral, topographic thickness variability, and
epithelial thickness range. These data were collected as follows (Figure 2): Each thickness map was divided into 17 sections (2.0 mm diameter pupil center disk of 12.56 mm2 area; 8
sectors [octants] within the annulus between the 2.0 mm and
5.0 mm zones, each of 8.24 mm2 areas; and 8 sectors [octants]
within the annulus of the 5.0 to 6.0 mm zones, each of
4.32 mm2 areas). For each of these sections, the mean epithelial thickness was displayed numerically in integer form with
a minimum difference of 1 mm over the corresponding area.
In this study, the reported center epithelium thickness was
taken from the integer indication over the center 2.0 mm
disk. The mean epithelial thickness was computed by the
mean of all segments, and the peripheral epithelial thickness
was computed by the mean of the thickness corresponding
to 18 equispaced points along the 5.0 mm radius (data harvested by mouse-over indication over the epithelial thickness map). The superior, inferior, minimum, maximum,
and topographic epithelial thickness variability (computed
by the standard deviation [SD] of the 17 thickness values)
were provided in tabular form by the software of the
AS-OCT device (Figure 2). The thickness range was computed
as follows: minimum epithelial thickness – maximum epithelial thickness.
Descriptive statistics, linear regression analysis to look for
possible correlations, paired analysis t tests, and analysis of
variance were performed using Minitab software (version
16.2.3, Minitab, Ltd.) and Origin Lab software (version 9,
Originlab Corp.). Paired-analysis P values less than 0.05
were considered an indication of statistically significant
results.
RESULTS
Table 1 shows the CCT, minimum corneal thickness,
epithelial thicknesses, topographic thickness variability,
1599
and epithelial thickness range measured by AS-OCT in
the 3 groups.
Group A (Athens protocol) comprised 175 eyes, 74
of women and 101 of men. The mean patient age at
the time of surgery was 26.8 years G 7.2 (SD) (range
18 to 48 years). There were 87 right eyes and 88 left
eyes. The Athens protocol treatment was uneventful
in all cases.
Group B (untreated keratoconic) comprised 193
eyes, 92 of women and 101 of men. The mean patient
age at the time of examination was 31.1 G 9.9 years
(range 18.0 to 51.0 years). There were 91 right eyes
and 102 left eyes.
Group C (control) comprised 160 eyes, 67 of women
and 93 of men. The mean patient age at the time of examination was 35.45 G 9.55 years (range 18.0 to 52.0
years). There were 74 right eyes and 86 left eyes.
Epithelial Thickness
In Group A, the difference in the center epithelial
thickness between each postoperative timepoint was
statistically significant (all P!.05). The difference in
the mean center epithelial thickness (!4.31 mm; 95%
confidence interval [CI], !6.31 to !2.30) between
Group A 1 year after treatment and Group B at the
time of examination was statistically significant
(P!.05, 2-sample t test). The difference in the mean
center epithelial thickness (!4.75 mm, 95% CI, !6.59
to !2.92) between Group A 1 year after treatment
and Group C at the time of examination was also statistically significant (P!.05) (Figure 3).
In Group A, the difference in topographic thickness
variability between each postoperative timepoint was
statistically significant (all P!.05). Figure 4 shows the
epithelial thickness variability and range by group.
DISCUSSIONS
Until recently, high-frequency UBM had been the gold
standard for in vivo corneal epithelial 3-D imaging.12
The recent, rapid development and current highspeed imaging capabilities of AS-OCT13–15 have
made acquisition of in vivo 3-D pachymetry corneal
maps reliable and fast.16–19 Software refinement also
enables clinical assessment of corneal asymmetry
and focal thinning parameters for keratoconus classification.20 In addition, the higher axial resolution,
increased accuracy, and finer image-processing capabilities of the current AS-OCT imaging systems have
enabled, among other things, 3-D imaging of epithelial
thickness.7
Epithelial thickness and irregularity indices (eg,
center and mean epithelial thickness, epithelial thickness topographic irregularity, and thickness range)
1600
Table 1. Central corneal thickness (CCT), minimum corneal thickness, epithelial thicknesses, topographic thickness variability, and epithelial thickness range measured by the AS-OCT in the 3 groups. All units are in microns.
Epithelial Thickness
Group
Group A (AP treated)
1 month
Mean
SD
Max
Min
6 months
Mean
SD
Max
Min
1 year
Mean
SD
Max
Min
Group B (KCN)
Mean
SD
Max
Min
Group C (healthy)
Mean
SD
Max
Min
CCT
MinCT
Center
Superior
Inferior
Minimum
Maximum
Mean
Mid
Topographic
Variability
382.7
32.8
444
336
330.5
34.5
432
248
42.6
7.3
52
36
43.2
5.3
51
36
44.5
6.0
53
39
33.3
7.8
45
18
58.0
7.2
74
49
43.9
6.0
52.1
38.7
44.2
6.0
52.1
38.9
5.4
3.0
13.5
2.7
!24.7
12.8
!10.0
!54.0
397.7
36.9
481
300
341.8
42.2
412
242
46.38
6.80
58
34
47.3
7.0
61
33
47.9
5.7
57
38
36.7
5.9
46
22
58.5
10.0
78
44
47.4
5.6
56.9
38.0
47.6
5.4
58.3
38.8
5.1
1.9
9.3
2.1
!21.8
8.5
!9.0
!39.0
435.8
42.0
550
351
365.9
50.0
500
252
47.8
4.6
64
33
49.7
6.0
61
36
48.9
3.9
62
38
38.5
8.4
55
18
59.0
6.0
75
44
48.9
5.3
60.6
37.3
49.2
5.2
59.9
38.2
4.6
1.6
8.1
1.6
!19.9
7.2
!6.0
!34.0
482.7
41.7
570
356
439.1
62.8
548
193
52.1
6.8
72
36
55.4
6.5
76
42
50.0
5.3
69
33
41.3
8.1
60
19
63.1
8.5
94
49
52.5
5.2
70.3
43.5
52.6
5.1
70.0
43.6
5.8
3.4
17.8
1.3
!21.8
12.1
!4.0
!66.0
532.4
28.5
592
462
525.1
27.9
580
455
52.5
3.2
59
45
51.4
3.4
60
44
53.1
3.3
59
45
48.5
4.0
57
28
55.3
3.7
64
46
52.2
3.2
59
45
52.2
3.2
60
45
1.6
0.8
5.6
0.6
!6.9
3.3
!3.0
!29.0
Range
AT Z Athens Protocol; CCT Z central corneal thickness; KCN Z keratoconus, no treatment; Mid Z midperipheral; MinCT Z minimum corneal thickness
measured quantitatively with AS-OCT can serve as
possible indicators of cornea instability, including ectasia and keratoconus.14 In this study, we evaluated
these parameters with a Fourier-domain AS-OCT system in a large group of keratoconic patients who had
combined treatment of excimer laser anterior surface
normalization and simultaneous high-fluence accelerated CXL. This study adds new information based on
its large group of treated keratoconic eyes and its comparison with untreated keratoconic eyes and healthy
eyes. In addition, our study was performed with a
commercially available AS-OCT system whose use
may become more widespread in clinical settings.
Our findings confirm compensatory epithelial thickness changes previously described after various refractive corneal ablation procedures.21,22,A
The epithelial thickness and irregularity assessment in the Athens protocol–treated Group A
suggests short-term variability in corneal thickness
distribution between the third month and the sixth
month.3 Specifically, in our study, the corneal and
epithelial thickness distributions were characterized
by large deviations that gradually became less irregular. The mean SD at the center epithelial thickness of
7.36 mm at 1 month gradually decreased to 6.80 at
3 months and to 4.57 mm at 1 year. The SD in Group
B (untreated keratoconic) and in Group C (control)
was 6.79 mm and 3.23 mm, respectively. In addition
to fluctuating less between different eyes, the epithelial thickness in Group A progressed toward a
reduced mean topographic variability and mean
thickness range (from 5.43 mm and !24.69 mm to
4.64 mm and !19.94 mm, respectively). Both metrics
were more regular than in Group B (5.77 mm and
!21.83 mm, respectively). These results indicate that
the epithelial thickness distribution was more uniform
in the Athens protocol–treated group than in the
untreated group of keratoconic eyes and had less overall thickness, as suggested by the reduced mean and
center thickness values.
1601
1602
3.
4.
5.
6.
7.
8.
9.
Figure 3. Mean and center epithelial thicknesses in the 3 groups.
Error bars correspond to the SD (KCN Z keratoconus, no treatment).
The findings in the current study agree with those in
our previous study1; that is, although an overall thicker
epithelium with large variations can be observed clinically and topographically in eyes with keratoconus, in
eyes treated with CXL the variability in epithelium
thickness and topographic thickness decreased by a
statistically significant margin and was more uniform.
We have theorized that epithelial hyperplasia in biomechanically unstable corneas (ie, increased epithelial
regrowth activity) might be associated with a more
elastic cornea.1 The laboratory and clinical findings of
increased corneal rigidity after CXL are widely
accepted,23–25 including in studies of accelerated highfluence CXL.26
In conclusion, we present the results in a comprehensive study of the postoperative development of
corneal epithelial thickness distribution after keratoconus management using combined anterior corneal
normalization by topography-guided excimer ablation and accelerated CXL. The epithelial healing processes can be monitored by AS-OCT with ease in a
clinical setting, expanding the clinical application of
this technology. Our findings suggest less topographic
variability and overall reduced epithelial thickness
distribution in keratoconus eyes treated with CXL using the Athens protocol.
Figure 4. Epithelial thickness variability and range in the 3 groups.
Error bars correspond to the SD (KCN Z keratoconus, no treatment).
10.
WHAT WAS KNOWN
! Postoperative epithelial remodeling after partial anterior
surface normalization with an excimer laser and highfluence CXL, assessed with high-frequency scanning
UBM, results in reduced overall epithelial thickness and
topographic variability.
11.
12.
WHAT THIS PAPER ADDS
! Detailed follow-up of Athens protocol–treated eyes up to 1
year confirmed previous ultrasound findings of the overall
thinner and smoother epithelial thickness profiles
compared with the profiles of untreated keratoconic eyes.
13.
REFERENCES
1. Kanellopoulos AJ, Aslanides IM, Asimellis G. Correlation between epithelial thickness in normal corneas, untreated ectatic
corneas, and ectatic corneas previously treated with CXL; is
overall epithelial thickness a very early ectasia prognostic factor? Clin Ophthalmol 2012; 6:789–800. Available at: http://
www.ncbi.nlm.nih.gov/pmc/articles/PMC3373227/pdf/opth-6-789.
pdf. Accessed June 11, 2014
2. Kanellopoulos AJ. Long term results of a prospective randomized bilateral eye comparison trial of higher fluence, shorter
duration ultraviolet A radiation, and riboflavin collagen cross
14.
15.
linking for progressive keratoconus. Clin Ophthalmol 2012;
6:97–101. Available at: http://www.ncbi.nlm.nih.gov/pmc/
articles/PMC3261695/pdf/opth-6-097.pdf. Accessed June 11, 2014
Kanellopoulos AJ, Asimellis G. Keratoconus management: longterm stability of topography-guided normalization combined with
high fluence CXL stabilization (the Athens Protocol). J Refract
Surg 2014; 30:88–92
Kanellopoulos AJ, Asimellis G. Introduction of quantitative and
qualitative cornea optical coherence tomography findings
induced by collagen cross-linking for keratoconus: a novel effect
measurement benchmark. Clin Ophthalmol 2013; 7:329–335.
Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC
3577010/pdf/opth-7-329.pdf. Accessed June 11, 2014
Kanellopoulos AJ, Asimellis G. In vivo three-dimensional
corneal epithelium imaging in normal eyes by anteriorsegment optical coherence tomography: a clinical reference
study. Cornea 2013; 32:1493–1498
! A. Ocular surface
Francoz M, Karamoko I, Baudouin C, Labbe
epithelial thickness evaluation with spectral-domain optical
coherence tomography. Invest Ophthalmol Vis Sci 2011;
52:9116–9123. Available at: http://www.iovs.org/content/52/
12/9116.full.pdf. Accessed June 11, 2014
Kanellopoulos AJ, Asimellis G. In vivo 3-dimensional corneal
epithelial thickness mapping as an indicator of dry eye: preliminary clinical assessment. Am J Ophthalmol 2014; 157:63–68
Chen TC, Cense B, Pierce MC, Nassif N, Park BH, Yun SH,
White BR, Bouma BE, Tearney GJ, de Boer JF. Spectral domain optical coherence tomography; ultra-high speed, ultra-high resolution
ophthalmic imaging. Arch Ophthalmol 2005; 123:1715–1720
Oh W-Y, Vakoc BJ, Shishkov M, Tearney GJ, Bouma BE. O400
kHz repetition rate wavelength-swept laser and application to
high-speed optical frequency domain imaging. Opt Lett 2010;
35:2919–2921. Available at: http://www.ncbi.nlm.nih.gov/pmc/
articles/PMC3003227/pdf/nihms255350.pdf. Accessed June 11, 2014
Kanellopoulos AJ, Asimellis G. Long term bladeless LASIK outcomes with the FS200 femtosecond and EX500 excimer laser
workstation: the Refractive Suite. Clin Ophthalmol 2013; 7:261–
269. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/
PMC3583408/pdf/opth-7-261.pdf. Accessed June 11, 2014
Kanellopoulos AJ, Asimellis G. Correlation between central
corneal thickness, anterior chamber depth, and corneal keratometry as measured by Oculyzer II and WaveLight OB820 in preoperative cataract surgery patients. J Refract Surg 2012; 28:895–900
Reinstein DZ, Gobbe M, Archer TJ, Silverman RH, Coleman DJ.
Epithelial, stromal, and total corneal thickness in keratoconus:
three-dimensional display with Artemis very-high frequency digital ultrasound. J Refract Surg 2010; 26:259–271. Available at:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3655809/pdf/nihms
211821.pdf. Accessed June 11, 2014
Potsaid B, Baumann B, Huang D, Barry S, Cable AE,
Schuman JS, Duker JS, Fujimoto JG. Ultrahigh speed 1050nm
swept source/Fourier domain OCT retinal and anterior segment
imaging at 100,000 to 400,000 axial scans per second. Opt
Exp 2010; 18:20029–20048. Available at: http://www.ncbi.nlm.
nih.gov/pmc/articles/PMC3136869/pdf/nihms304233.pdf. Accessed June 11, 2014
Rocha KM, Perez-Straziota CE, Stulting RD, Randleman JB.
SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes.
J Refract Surg 2013; 29:173–179
Ge L, Yuan Y, Shen M, Tao A, Wang J, Lu F. The role of axial
resolution of optical coherence tomography on the measurement of corneal and epithelial thicknesses. Invest Ophthalmol
Vis Sci 2013; 54:746–755. Available at: http://www.iovs.org/
content/54/1/746.full.pdf. Accessed June 11, 2014
16. Wojtkowski M, Kaluzny B, Zawadzki RJ. New directions in
ophthalmic optical coherence tomography. Optom Vis Sci
2012; 89:524–542. Available at: http://journals.lww.com/
optvissci/Fulltext/2012/05000/New_Directions_in_Ophthalmic_
Optical_Coherence.4.aspx. Accessed June 11, 2014
17. Khurana RN, Li Y, Tang M, Lai MM, Huang D. High-speed optical coherence tomography of corneal opacities. Ophthalmology
2007; 114:1278–1485
18. Li Y, Shekhar R, Huang D. Corneal pachymetry mapping with
high-speed optical coherence tomography. Ophthalmology
2006; 113:792–799.e2
19. Dutta D, Rao HL, Addepalli UK, Vaddavalli PK. Corneal thickness in keratoconus; comparing optical, ultrasound, and optical
coherence tomography pachymetry. Ophthalmology 2013;
120:457–463
20. Kanellopoulos AJ, Chiridou M, Asimellis G. Optical coherence
tomography-derived corneal thickness asymmetry indices: clinical reference study in 561 normal eyes. In press, J Cataract
Refract Surg 2014
21. Gauthier CA, Holden BA, Epstein D, Tengroth B, Fagerholm P,
€m H. Role of epithelial hyperplasia in regresHamberg-Nystro
sion following photorefractive keratectomy. Br J Ophthalmol
1996; 80:545–548. Available at: http://bjo.bmj.com/content/80/
6/545.full.pdf. Accessed June 11, 2014
22. Erie JC, Patel SV, McLaren JW, Ramirez M, Hodge DO,
Maguire LJ, Bourne WM. Effect of myopic laser in situ keratomileusis on epithelial and stromal thickness; a confocal microscopy
study. Ophthalmology 2002; 109:1447–1452
23. Raiskup-Wolf F, Hoyer A, Spoerl E, Pillunat LE. Collagen crosslinking with riboflavin and ultraviolet-A light in keratoconus: longterm results. J Cataract Refract Surg 2008; 34:796–801
# E, Trazza S, Rosetta P, Vinciguerra R,
24. Vinciguerra P, Albe
Seiler T, Epstein D. Refractive, topographic, tomographic, and
aberrometric analysis of keratoconic eyes undergoing corneal
cross-linking. Ophthalmology 2009; 116:369–378
25. O’Brart DPS, Kwong TQ, Patel P, McDonald RJ, O’Brart NA.
Long-term follow-up of riboflavin/ultraviolet A (370 nm) corneal
collagen cross-linking to halt the progression of keratoconus.
Br J Ophthalmol 2013; 97:433–437. Available at: http://bjo.
bmj.com/content/97/4/433.full.pdf. Accessed June 11, 2014
26. Schumacher S, Oeftiger L, Mrochen M. Equivalence of biomechanical changes induced by rapid and standard corneal crosslinking, using riboflavin and ultraviolet radiation. Invest Ophthalmol
Vis Sci 2011; 52:9048–9052. Available at: http://www.iovs.org/
content/52/12/9048.full.pdf. Accessed June 11, 2014
OTHER CITED MATERIAL
A. Reinstein DZ, Aslanides IM, Patel S, Silverman RH, Coleman
DJ, “Epithelial Lenticular Types of Human Cornea: Classification and Analysis of Influence on PRK,” poster presented at
the annual meeting of the American Academy of Ophthalmology, Atlanta, Georgia, USA, October 1995. Abstract available in: Ophthalmology 1995; 102(suppl):S156
First author:
Anastasios John Kanellopoulos, MD
Laservision.gr Clinical and Research
Institute, Athens, Greece
ORIGINAL ARTICLE
The Athens Protocol/Kanellopoulos & Asimellis
Keratoconus Management: Long-Term
Stability of Topography-Guided Normalization
Combined With High-Fluence CXL
Stabilization (The Athens Protocol)
PURPOSE: To investigate refractive, topometric, pachymetric, and visual rehabilitation changes induced by anterior surface normalization for keratoconus by partial
topography-guided excimer laser ablation in conjunction
with accelerated, high-fluence cross-linking.
METHODS: Two hundred thirty-one keratoconic cases
subjected to the Athens Protocol procedure were studied for visual acuity, keratometry, pachymetry, and anterior surface irregularity indices up to 3 years postoperatively by Scheimpflug imaging (Oculus Optikgeräte
GmbH, Wetzlar, Germany).
RESULTS: Mean visual acuity changes at 3 years
postoperatively were +0.38 ± 0.31 (range: -0.34
to +1.10) for uncorrected distance visual acuity and
+0.20 ± 0.21 (range: -0.32 to +0.90) for corrected
distance visual acuity. Mean K1 (flat meridian) keratometric values were 46.56 ± 3.83 diopters (D) (range:
39.75 to 58.30 D) preoperatively, 44.44 ± 3.97 D
(range: 36.10 to 55.50 D) 1 month postoperatively,
and 43.22 ± 3.80 D (range: 36.00 to 53.70 D) up to
3 years postoperatively. The average Index of Surface
Variance was 98.48 ± 43.47 (range: 17 to 208) preoperatively and 76.80 ± 38.41 (range: 7 to 190) up
to 3 years postoperatively. The average Index of Height
Decentration was 0.091 ± 0.053 µm (range: 0.006
to 0.275 µm) preoperatively and 0.057 ± 0.040 µm
(range: 0.001 to 0.208 µm) up to 3 years postoperatively. Mean thinnest corneal thickness was 451.91
± 40.02 µm (range: 297 to 547 µm) preoperatively,
353.95 ± 53.90 µm (range: 196 to 480 µm) 1 month
postoperatively, and 370.52 ± 58.21 µm (range: 218
to 500 µm) up to 3 years postoperatively.
CONCLUSIONS: The Athens Protocol to arrest keratectasia progression and improve corneal regularity demonstrates safe and effective results as a keratoconus
management option. Progressive potential for long-term
flattening validates using caution in the surface normalization to avoid overcorrection.
[J Refract Surg. 2014;30(2):88-92.]
K
eratoconus is a degenerative bilateral, noninflammatory disorder characterized by ectasia, thinning,
and irregular corneal topography.1 The disorder
usually has onset at puberty and often progresses until the
third decade of life, may manifest asymmetrically in the two
eyes of the same patient, and can present with unpredictable
visual acuity, particularly in relation to corneal irregularities.2
One of the acceptable options3 for progressive keratoconus
management is corneal collagen cross-linking (CXL) with riboflavin and ultraviolet-A.4
To further improve the topographic and refractive outcomes, CXL can be combined with customized anterior surface normalization.5-7 Our team has developed a procedure8,9
we have termed the Athens Protocol,10 involving sequentially
excimer laser epithelial debridement (50 µm), partial topography-guided excimer laser stromal ablation, and high-fluence ultraviolet-A irradiation (10 mW/cm2), accelerated (10’,
or minutes) CXL. Early results11 and anterior segment optical
coherence tomography quantitative findings12 are indicative
of the long-term stability of the procedure.
Detailed studies on postoperative visual rehabilitation and
anterior surface topographic changes by such combined CXL
procedures are rare,13-16 particularly those reporting results
longer than 1 year. This study aims to investigate safety and
efficacy of the Athens Protocol procedure by analysis of longterm (3-year) refractive, topographic, pachymetric, and visual
rehabilitation changes on clinical keratoconus management
with the Athens Protocol in a large number of cases.
PATIENTS AND METHODS
This clinical study received approval by the Ethics Committee of our Institution and adhered to the tenets of the Declaration
From Laservision.gr Eye Institute, Athens, Greece (AJK, GA); and New York
University School of Medicine, New York, New York (AJK).
Submitted: April 6, 2013; Accepted: August 21, 2013; Posted online: January
31, 2014
Dr. Kanellopoulos is a consultant for Alcon/WaveLight. The remaining author
has no financial or proprietary interest in the materials presented herein.
Correspondence: Anastasios John Kanellopoulos, MD, 17 Tsocha str. Athens,
Greece Postal Code 11521. E-mail: [email protected]
doi:10.3928/1081597X-20140120-03
88
Postoperative
Value
Preop
1 Month
3 Months
6 Months
12 Months
24 Months
36 Months
UDVA
Average
0.18
0.42
0.49
0.55
0.57
0.59
0.59
SD (±)
±0.20
±0.27
±0.29
±0.29
±0.28
±0.28
±0.28
n/a
+0.23
+0.30
+0.36
+0.36
+0.39
+0.38
Gain/loss
CDVA
Anastasios John Kanellopoulos, MD; George Asimellis, PhD
ABSTRACT
TABLE 1
Visual Acuity Data (N = 231 Eyes)a
Copyright © SLACK Incorporated
Average
0.62
0.69
0.76
0.80
0.81
0.82
0.82
SD (±)
±0.23
±0.22
±0.20
±0.20
±0.19
±0.19
±0.19
n/a
+0.07
+0.14
+0.18
+0.18
+0.19
+0.20
Gain/loss
preop = preoperative; UDVA = uncorrected distance visual acuity; SD = standard deviation; n/a = not applicable; CDVA = corrected distance visual acuity
a
Expressed as the difference of postoperative minus preoperative values (gain/loss). Units are decimal.
of Helsinki. Written informed consent was obtained from
each participant at the time of the intervention or the first
clinical visit.
PATIENT INCLUSION CRITERIA
Two hundred thirty-one consecutive keratoconic
cases subjected to the Athens Protocol procedure between 2008 and 2010 were investigated. All procedures were performed by the same surgeon (AJK) using the Alcon/WaveLight 400 Hz Eye-Q17 or the EX500
excimer lasers.18 Inclusion criteria were clinical diagnosis of progressive keratoconus, minimum age of
17 years, and corneal thickness of at least 300 µm. All
participants completed an uneventful Athens Protocol
procedure and all 231 eyes were observed for up to 3
years. Exclusion criteria were systemic disease, previous eye surgery, chemical injury or delayed epithelial
healing, and pregnancy or lactation (female patients).
MEASUREMENTS AND ANALYSIS
Postoperative evaluation included uncorrected distance visual acuity (UDVA), manifest refraction, corrected distance visual acuity (CDVA) with this refraction, and slit-lamp biomicroscopy for clinical signs of
CXL.12 For the quantitative assessment of the induced
corneal changes, postoperative evaluation was performed by a Pentacam Scheimpflug imaging device
(Oculyzer II, WavLight AG, Erlangen, Germany)19 and
processed via Examination Software (Version 1.17r47).
Specific anterior surface irregularity indices provided
by the Scheimpflug imaging analysis were evaluated
in addition to keratometric and pachymetric values.
These indices are employed in grading and classification based on the Amsler and Krumeich criteria.20,21
These are the Index of Surface Variance, an expression
of anterior surface curvature irregularity, and the Index of Height Decentration, calculated with Fourier
analysis of corneal height (expressed in microns) to
Journal of Refractive SurgeryÊUÊ6°ÊÎä]Ê °ÊÓ]ÊÓä£{
quantify the degree of cone decentration.22 Index of
Surface Variance and Index of Height Decentration
were computed for the 8-mm diameter zone.
Descriptive and comparative statistics, analysis of
variance, and linear regression were performed by
Minitab version 16.2.3 (MiniTab Ltd., Coventry, UK)
and Origin Lab version 9 (OriginLab Corp., Northampton, MA). Paired analysis P values less than .05 were
considered statistically significant. Visual acuity is reported decimally and keratometry in diopters (D). Results are reported as mean ± standard deviation and
range as minimum to maximum.
RESULTS
The 231 eyes enrolled belonged to 84 female and 147
male participants. Mean participant age at the time of
the operation was 30.1 ± 7.5 years (range: 17 to 57 years).
All eyes were followed up to the 3-year follow-up.
VISUAL ACUITY CHANGES
Table 1 presents preoperative and postoperative
UDVA and CDVA. UDVA increased by +0.38 ± 0.31
(range: -0.34 to +1.10) and CDVA by +0.20 ± 0.21 (range:
-0.32 to +0.90). Figure 1 illustrates, in the form of box
plots, visual acuity gained or lost 3 years postoperatively. These graphs (the 95% median confidence range
box) indicate that 95% of the cases had at least +0.1 increase in UDVA and 95% had positive change in CDVA.
KERATOMETRIC AND ANTERIOR SURFACE INDICES
PROGRESSION
Anterior keratometry continued to flatten over the
3-year follow-up (Figure 2). Descriptive statistics for
anterior keratometry, preoperatively and postoperatively, are presented in Table A (available in the online
version of this article).
The values for the Index of Surface Variance
and the Index of Height Decentration continued to
89
TABLE 2
Thinnest Corneal Thickness Measured by the Scheimpflug Device (N = 231 Eyes) (µm)
Postoperative
Value
Preoperative
1 Month
3 Months
6 Months
12 Months
24 Months
Average
451.91
353.95
356.67
364.92
367.15
370.52
36 Months
370.52
SD
±40.02
±53.90
±56.41
±53.64
±55.70
±57.84
±58.21
Maximum
547
480
501
501
490
500
500
Minimum
297
196
179
220
216
218
218
SD = standard deviation
Figure 1. Change (gain/loss) in visual acuity, expressed as the difference of postoperative minus preoperative values (expressed decimally),
showing median level (indicated by (+), average symbol (x), 95% median
confidence range box (red borderline boxes), and interquartile intervals
range box (black borderline boxes).
Figure 3. Anterior surface topometric indices Index of Surface Variance
(no units) and Index of Height Decentration (units µm) as measured by the
Scheimpflug imaging device (Oculyzer II, WavLight AG, Erlangen, Germany)
preoperatively, 1 month postoperatively, and up to 36 months postoperatively.
decrease over time (Figure 3, Table B, available in
the online version of this article).
PACHYMETRIC PROGRESSION
The thinnest corneal decreased as a result of excimer laser ablation but then stabilized over time without additional thinning (Table 2).
DISCUSSION
Many reports describe the effects of CXL with or
without same-session excimer laser ablation corneal
normalization.3 There is general consensus that the intervention strengthens the cornea, helps arrest the ectasia progression, and improves corneal keratometric
values, refraction, and visual acuity.
The key question is the long-term stability of these induced changes. For example, is the cornea ‘inactive’ after
90
Figure 2. Anterior keratometry (K1 flat and K2 steep) as measured by the
Scheimpflug device (Oculyzer II, WavLight AG, Erlangen, Germany) preoperatively up to 3 years postoperatively. All units in keratometric diopters (D).
the intervention and, if not, is there steepening or flattening and/or thickening or thinning? These issues are even
more applicable in the case of the Athens Protocol, due
to the partial corneal surface ablation. Ablating a thin,
ectatic cornea may sound unorthodox. However, the goal
of the topography-guided ablation is to normalize the anterior cornea and thus help improve visual rehabilitation
to a step beyond that a simple CXL would provide.
This study aims to address some of the above issues.
The large sample and follow-up time permit sensitive
analysis with confident conclusion of postoperative efficacy. We monitored visual acuity changes and for the
quantitative assessment we chose to standardize on one
Scheimpflug screening device and to focus on key parameters of visual acuity, keratometry, pachymetry, and
anterior surface indices.23 All of these parameters reflect
changes induced by the procedure and describe postoperative progression. However, variations in the two anterior
surface indices (Index of Surface Variance and Index of
Height Decentration) may provide a more valid analysis
than keratometry and visual function.24 Our results indicate that the apparent disadvantage of thinning the cornea
is balanced by a documented long-term rehabilitating improvement and synergy from the CXL component.
VISUAL ACUITY CHANGES
Based on our results, the Athens Protocol appears
to result in postoperative improvement in both UDVA
and CDVA. Average gain/loss in visual acuity was consistently positive, starting from the first postoperative
month, with gradual and continuous improvement toward the 3-year visit. These visual rehabilitation improvements appear to be superior to those reported in
cases of simple CXL treatment.25
However, it is noted that the visual acuity presented
with large variations. The standard deviation of UDVA
was ±0.20 preoperatively and ±0.28 postoperatively.
Likewise, the standard deviation of CDVA was ±0.23
preoperatively and ±0.20 postoperatively.
We theorize that the reason for visual acuity in keratoconic cases having such large fluctuations (and often
being unexpectedly good) can be attributed to a ‘multifocal’ and ‘soft’ (ie, adaptable) cornea, in addition to
advanced neural processing in the individual visual
system. However, these ‘advantages’ are essentially negated with CXL treatment, which stiffens the cornea.
Over time, possibly due to further topography improvement and adaptation to the partially normalized cornea,
a noteworthy improvement in visual acuity is observed.
KERATOMETRIC AND ANTERIOR SURFACE INDICES
PROGRESSION
After the 1-month visit, keratometric values are reduced. This progressive potential for long-term flattening has been clinically observed in many cases over at
least 10 years. Peer-reviewed reports on this matter have
been rare and only recent.26,27
The two anterior surface indices, Index of Surface
Variance and Index of Height Decentration, also demonstrated postoperative improvement. A smaller value
is indication of corneal normalization (lower Index
of Surface Variance, less irregular surface, lower Index of Height Decentration, cone less steep and more
central). These changes are therefore suggestive of
corneal topography improvement, in agreement with
other smaller sample studies.13 Such changes in Index
of Surface Variance and Index of Height Decentration
have been reported only recently.28
The initial more ‘drastic’ change of the Index of
Height Decentration can be justified by the chief objective of surface normalization, cone centering,6 which is
noted even by the first month. The subsequent surface
normalization, as also indicated by keratometric flattening, suggests further anterior surface improvement.
PACHYMETRIC PROGRESSION
As expected by the fact that Athens Protocol includes a partial stromal excimer ablation, there is
Journal of Refractive SurgeryÊUÊ6°ÊÎä]Ê °ÊÓ]ÊÓä£{
reduction of postoperative corneal thickness, manifested by the thinnest corneal thickness. What seemed
to be a ‘surprising’ result is that the cornea appears to
rebound, by gradually thickening, up to 3 years postoperatively. Postoperative corneal thickening after
the 1-month ‘lowest thickness baseline’ has also been
discussed recently.29,30 In another report,31 the lowest
thinnest corneal thickness was noted at the 3-month
interval. In that study of 82 eyes treated only with
CXL, the average cornea thickened by +24 µm after 1
year compared to the 3-month baseline. In our study of
212 eyes treated with the Athens Protocol procedure,
the cornea thickening rate after the baseline first postoperative month was approximately half (+12 µm over
the first year), in agreement with a recent publication.29
Therefore, it is possible that stromal changes initiated by the CXL procedure are not just effective in
halting ectasia, but are prompting corneal surface
flattening and thickening, which appears to be longer
lasting than anticipated.
We note, however, that CXL alone results not just in
corneal reshaping, but also in stromal density and refractive index, both possibly influencing the reported thickness by the Scheimpflug device. Therefore, true corneal
thickness differences may not be accurately explored by
Scheimpflug imaging due to the principle of operation
(densitometry), which has been our clinical experience
with abnormal density corneas (ie, corneal scars or arcus senilis corneas). Further studies of corneal thickness
chances by modalities, such as anterior segment optical
coherence tomography, which currently also measure
epithelial thickness,32 may be warranted. In addition, corneal biomechanical analysis and corneal volume studies
may be necessary to further validate such findings.
Our study indicates a significant improvement in all
parameters studied. The changes induced by the procedure indicate a consistent trend toward improved
visual rehabilitation, corneal flattening (validating ectasia arrest), and anterior surface improvement. The
Athens Protocol procedure demonstrates impressive
refractive, keratometric, and topometric results. Progressive potential for long-term flattening documented
91
in this study suggests employment of caution in the
surface normalization process to avoid overcorrection.
AUTHOR CONTRIBUTIONS
Study concept and design (AJK, GA); data collection (AJK, GA); analysis
and interpretation of data (AJK, GA); drafting of the manuscript (GA);
critical revision of the manuscript (AJK, GA); statistical expertise (GA);
administrative, technical, or material support (AJK); supervision (AJK)
REFERENCES
1. Gordon-Shaag A, Millodot M, Shneor E. The epidemiology
and etiology of keratoconus. Int J Keratoco Ectatic Corneal Dis.
2012;1:7-15.
2. Katsoulos C, Karageorgiadis L, Mousafeiropoulos T, Vasileiou
N, Asimellis G. Customized hydrogel contact lenses for keratoconus incorporating correction for vertical coma aberration.
Ophthalmic Physiol Opt. 2009;29:321-329.
3. Chan E, Snibson GR. Current status of corneal collagen cross-linking for keratoconus: a review. Clin Exp Optom. 2013;96:155-164.
4. Kanellopoulos AJ. Collagen cross-linking in early keratoconus
with riboflavin in a femtosecond laser-created pocket: initial
clinical results. J Refract Surg. 2009;25:1034-1037.
5. Kanellopoulos AJ, Binder PS. Collagen cross-linking (CCL) with
sequential topography-guided PRK: a temporizing alternative for
keratoconus to penetrating keratoplasty. Cornea. 2007;26:891-895.
6. Kanellopoulos AJ. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for
treatment of keratoconus. J Refract Surg. 2009;25:S812-S818.
7. Labiris G, Giarmoukakis A, Sideroudi H, Gkika M, Fanariotis
M, Kozobolis V. Impact of keratoconus, cross-linking and crosslinking combined with photorefractive keratectomy on self-reported quality of life. Cornea. 2012;31:734-739.
8. Kanellopoulos AJ, Binder PS. Management of corneal ectasia
after LASIK with combined, same-day, topography-guided partial transepithelial PRK and collagen cross-linking: the athens
protocol. J Refract Surg. 2011;27:323-331.
9. Ewald M, Kanellopoulos J. Limited topography-guided surface
ablation (TGSA) followed by stabilization with collagen crosslinking with UV irradiation and ribofl avin (UVACXL) for keratoconus
(KC). Invest Ophthalmol Vis Sci. 2008;49:E-Abstract 4338.
10. Kanellopoulos AJ. Long term results of a prospective randomized
bilateral eye comparison trial of higher fluence, shorter duration
ultraviolet A radiation, and riboflavin collagen cross linking for
progressive keratoconus. Clin Ophthalmol. 2012;6:97-101.
11. Krueger RR, Kanellopoulos AJ. Stability of simultaneous topography-guided photorefractive keratectomy and riboflavin/
UVA cross-linking for progressive keratoconus: case reports. J
Refract Surg. 2010;26:S827-S832.
12. Kanellopoulos AJ, Asimellis G. Introduction of quantitative and
qualitative cornea optical coherence tomography findings, induced by collagen cross-linking for keratoconus; a novel effect
measurement benchmark. Clin Ophthalmol. 2013;7:329-335.
13. Greenstein SA, Fry KL, Hersh PS. Corneal topography indices after corneal collagen crosslinking for keratoconus and corneal ectasia: one-year results. J Cataract Refract Surg. 2011;37:1282-1290.
14. Guedj M, Saad A, Audureau E, Gatinel D. Photorefractive keratectomy in patients with suspected keratoconus: five-year follow-up. J Cataract Refract Surg. 2013;39:66-73.
15. Alessio G, L’abbate M, Sborgia C, La Tegola MG. Photorefractive keratectomy followed by cross-linking versus cross-linking
alone for management of progressive keratoconus: two-year
follow-up. Am J Ophthalmol. 2013;155:54-65.
92
16. Hersh PS, Greenstein SA, Fry KL. Corneal collagen crosslinking
for keratoconus and corneal ectasia: one-year results. J Cataract
Refract Surg. 2011;37:149-160.
17. Kanellopoulos AJ. Topography-guided hyperopic and hyperopic astigmatism femtosecond laser-assisted LASIK: long-term
experience with the 400 Hz eye-Q excimer platform. Clin Ophthalmol. 2012;6:895-901.
18. Kanellopoulos AJ, Asimellis G. Long-term bladeless LASIK outcomes
with the FS200 femtosecond and EX500 Excimer Laser workstation:
the Refractive Suite. Clin Ophthalmol. 2013;7:261-269.
TABLE A
Anterior Keratometry (K) Measured by the Scheimpflug Device (N = 231 Eyes)a
Postoperative
19. Kanellopoulos AJ, Asimellis G. Correlation between central corneal thickness, anterior chamber depth, and corneal keratometry
as measured by Oculyzer II and WaveLight OB820 in preoperative cataract surgery patients. J Refract Surg. 2012;28:895-900.
Value
Average
46.56
44.44
43.99
43.73
43.54
43.35
43.22
20. Krumeich JH, Daniel J, Knülle A. Live-epikeratophakia for keratoconus. J Cataract Refract Surg. 1998;24:456-463.
SD
±3.83
±3.97
±3.86
±3.76
±3.73
±3.74
±3.80
21. Faria-Correia F, Ramos IC, Lopes BT, et al. Topometric and tomographic indices for the diagnosis of keratoconus. Int J Kerat
Ectatic Dis. 2012;1:100-106.
Maximum
58.30
55.50
53.75
53.70
53.70
53.70
53.70
Minimum
39.75
36.10
36.10
36.10
36.10
36.10
36.00
22. Kanellopoulos AJ, Asimellis G. Revisiting keratoconus diagnosis and progression classification based on evaluation of corneal
asymmetry indices, derived from Scheimpflug imaging in keratoconic and suspect cases. Clin Ophthalmol. 2013;7:1539-1548.
23. Markakis GA, Roberts CJ, Harris JW, Lembach RG. Comparison
of topographic technologies in anterior surface mapping of keratoconus using two display algorithms and six corneal topography devices. Int J Kerat Ectatic Dis. 2012;1:153-157.
24. Ambrósio R Jr, Caiado AL, Guerra FP, et al. Novel pachymetric
parameters based on corneal tomography for diagnosing keratoconus. J Refract Surg. 2011;27:753-758.
25. Legare ME, Iovieno A, Yeung SN, et al. Corneal collagen crosslinking using riboflavin and ultraviolet A for the treatment of
mild to moderate keratoconus: 2-year follow-up. Can J Ophthalmol. 2013;48:63-68.
26. Vinciguerra P, Albè E, Trazza S, et al. Refractive, topographic, tomographic, and aberrometric analysis of keratoconic eyes undergoing corneal cross-linking. Ophthalmology. 2009;116:369-378.
27. Raiskup-Wolf F, Hoyer A, Spoerl E, Pillunat LE. Collagen crosslinking with riboflavin and ultraviolet-A light in keratoconus:
longterm results. J Cataract Refract Surg. 2008;34:796-801.
28. Kanellopoulos AJ, Asimellis G. Comparison of Placido disc and
Scheimpflug image-derived topography-guided excimer laser
surface normalization combined with higher influence CXL:
The Athens Protocol, in progressive keratoconus cases. Clin
Ophthalmol. 2013;7:1539-1548.
29. Mencucci R, Paladini I, Virgili G, Giacomelli G, Menchini U.
Corneal thickness measurements using time-domain anterior segment OCT, ultrasound, and Scheimpflug tomographer
pachymetry before and after corneal cross-linking for keratoconus. J Refract Surg. 2012;28:562-566.
30. O’Brart DP, Kwong TQ, Patel P, McDonald RJ, O’Brart NA.
Long-term follow-up of riboflavin/ultraviolet A (370 nm) corneal collagen cross-linking to halt the progression of keratoconus. Br J Ophthalmol. 2013;97:433-437.
31. Greenstein SA, Shah VP, Fry KL, Hersh PS. Corneal thickness
changes after corneal collagen crosslinking for keratoconus
and corneal ectasia: one-year results. J Cataract Refract Surg.
2011;37:691-700.
32. Kanellopoulos AJ, Asimellis G. Anterior segment optical coherence tomography: assisted topographic corneal epithelial thickness distribution imaging of a keratoconus patient. Case Rep
Ophthalmol. 2013;4:74-78.
Preop
1 Month
3 Months
6 Months
12 Months
24 Months
36 Months
K1 (flat)
K2 (steep)
Average
50.71
47.61
47.03
46.84
46.63
46.44
46.30
SD
±5.14
±5.15
±4.99
±4.92
±4.91
±4.88
±4.91
Maximum
66.62
62.75
61.25
60.25
60.00
60.00
60.00
Minimum
42.60
38.00
37.90
37.90
37.90
37.90
37.20
preop = preoperative; SD = standard deviation
a
All units in keratometric diopters (D).
TABLE B
Anterior Surface Topometric Indices and Postoperative Progression (N = 231 Eyes)
Postoperative
Value
Preoperative
1 Month
3 Months
6 Months
12 Months
24 Months
36 Months
Index of Surface Variance
Average
98.48
83.08
81.08
79.51
78.19
77.22
76.80
±43.47
±38.73
±38.13
±37.79
±38.04
±38.28
±38.41
Maximum
208
190
190
190
190
190
190
Minimum
17
18
17
16
15
14
7
SD
Index of Height Decentration (µm)
Average
0.091
0.063
0.061
0.059
0.058
0.058
0.057
±0.053
±0.041
±0.040
±0.040
±0.040
±0.040
±0.040
Maximum
0.275
0.208
0.208
0.208
0.208
0.208
0.208
Minimum
0.006
0.001
0.001
0.001
0.001
0.001
0.001
SD
SD = standard deviation
CLINICAL SCIENCE
Cornea ! Volume 33, Number 9, September 2014
Long-Term Safety and Efficacy of High-Fluence Collagen
Crosslinking of the Vehicle Cornea in Boston
Keratoprosthesis Type 1
Anastasios J. Kanellopoulos, MD,*† and George Asimellis, PhD*
Purpose: The aim of this study was to evaluate the safety and
efficacy of very high-fluence collagen crosslinking (CXL) as a means
of achieving increased corneal rigidity and reduced enzymatic
digestion in the vehicle cornea of Boston keratoprosthesis (KPro)
type 1.
Methods: Eleven consecutive patients fitted with a KPro (5 with
a previous repeat cornea graft failure, 4 with ocular cicatricial
pemphigoid, and 2 with chemical burn) underwent donor vehicle
cornea pretreatment with very high-fluence prophylactic CXL in a 2step procedure. First, the donor cornea was crosslinked with an
intrastromal riboflavin instillation through a femtosecond laser–created pocket. This was followed up with a superficial CXL treatment.
On the completion of the CXL pretreatment, the cornea center was
trephined with the femtosecond laser, and the KPro was fitted onto
the crosslinked donor cornea. Visual acuity, corneal surface, and
donor vehicle cornea stability were evaluated. Follow-up evaluations
were conducted over the next 9 years with a mean of 7.5 years.
Results: Mean uncorrected visual acuity improved from light
perception to 20/60. One patient required a follow-up surgery,
because of significant melt in the host cornea. None of the eyes
developed melts and/or infection, especially on the vehicle cornea on
which the KPro was fitted.
Conclusions: Pretreatment with intrastromal and superficial
very high-fluence CXL in conjunction with Boston type 1 KPro
seems to be a safe and effective adjunctive treatment for achieving
increased vehicle donor cornea rigidity. Additionally, there is an
increased resistance to enzymatic degradation. This application may
serve to enhance the biomechanical stability and external disease
Received for publication January 27, 2014; revision received April 30, 2014;
accepted May 5, 2014. Published online ahead of print July 9, 2014.
From the *Laservision.gr Eye Institute, Athens, Greece; and †Department of
Ophthalmology, NYU Medical School, New York, NY.
Presented in part at the CXL annual meeting in Dresden, Germany, in
December 2008.
A. J. Kanellopoulos: Alcon/WaveLight, Allegran, Avedro, i-Optics; Optovue.
The other author has no funding or conflicts of interest to disclose.
Design and conduct of the study (A.J.K.); collection (A.J.K.), management
(A.J.K.), analysis (A.J.K., G.A.), interpretation of the data (A.J.K., G.A.);
manuscript preparation (G.A., A.J.K.), manuscript review (A.J.K., G.A.),
manuscript approval (A.J.K., G.A.).
Reprints: Anastasios J. Kanellopoulos, MD, Clinical Professor of Ophthalmology, New York University Medical School, New York, NY, Laservision.gr Eye Institute, 17 Tsocha Street, Athens 115 21, Greece (e-mail:
[email protected]).
Copyright © 2014 by Lippincott Williams & Wilkins
914
resistance of the donor vehicle cornea in patients with advanced
external disease.
Key Words: prophylactic pretreatment with collagen crosslinking,
Boston keratoprosthesis type 1, Dohlman keratoprosthesis, severe
external disease, ocular cicatricial pemphigoid, chemical burn, repeat
cornea transplantation failure
(Cornea 2014;33:914–918)
E
xtreme external disease has been successfully treated over
the last few decades with allograft cornea transplantation,
relatively histocompatible limbal stem-cell transplantation, or
keratoprosthesis (KPro). There are several KPro variations.
Currently, the most prevalent in clinical practice are the Boston KPro,1–4 the AlphaCor,5 the odonto-KPro,6 the Fyodorov
KPro,7 and the KeraClear inlay KPro.
Our team has introduced the concept of accelerated,
high-fluence collagen crosslinking (CXL) in post–laser in
situ keratomileusis (LASIK) ectasia,8 and the use of prophylactic CXL in routine LASIK,9 in treatment of cornea
ectasia,10 and in attempting corneal deturgescence11 in bullous keratopathy.12
In our 20 years of experience in using the Boston KPro,
we encountered 2 significant complications: (1) melts and (2)
erosion of the donor and host cornea interface.13 When the
latter occurs, there is an increase in the risk of developing
infectious keratitis, which will significantly increase the risk
of potential endophthalmitis14 and may predispose prosthesis
exposure and/or infection. We hypothesized that the application of a prophylactic crosslinking treatment on the donor
vehicle cornea might help reduce the susceptibility of these
corneas to enzymatic digestion and cornea infection. This
work presents an evaluation of a longitudinal case series to
study the advantages of using CXL as a prophylactic intervention adjuvant to Boston KPro surgery.
This study describes the outcomes from 11 different
cases belonging to 11 different patients with external disease
and almost total visual disability who opted to undergo
Boston KPro type 1 in conjunction with prophylactic highfluence CXL in the donor vehicle cornea that would be used
for their KPro surgery. All the patients had debilitating visual
compromise. The most common preoperative diagnosis in
this group was repeat cornea graft failure (5 patients) with at
least 3 failed grafts in the past for each. The remaining
patients were diagnosed with ocular cicatricial pemphigoid15
(4 patients) and chemical corneal trauma (2 patients).
Preoperatively and postoperatively, we evaluated
uncorrected distance visual acuity (UDVA), best spectaclecorrected distance visual acuity (CDVA), subjective refraction, keratometry, and applied anterior-segment optical
coherence tomography (OCT).16 These examinations were
performed to evaluate the integrity of the donor vehicle
cornea on which the KPro was mounted, the host cornea,
and the donor–host interface. Macula and optic nerve OCT
screening was also performed to evaluate potential glaucomatous damage and/or macular edema.
Surgical Technique
The donor cornea was mounted on an artificial chamber
(Baron; Katena Products, Inc, Denville, NJ). A deep (350–
400 mm) lamellar central corneal pocket of an 8-mm diameter
was created using a femtosecond laser (the IntraLase FS60;
AMO, Abbott Park, IL, in the first 4 cases, and the WaveLight
FS200; Alcon, Ft Worth, TX, in the subsequent 7 cases).
This pocket was accessed from the anterior corneal surface
through a 3-mm channel. After a blunt olive-tip cannula was
placed into the pocket to facilitate injection, 0.1 mL of 0.1%
riboflavin sodium phosphate solution was injected into the
High-Fluence CXL in Keratoprosthesis
intrastromal pocket. Immediately after this, 4 minutes of
30 mW/cm2 ultraviolet-A irradiation for a total energy of
7.2 J/cm2 was directed onto the donor vehicle cornea.
After completing this step, the corneal epithelium was
scraped with a blunt crescent blade, and drops of 0.1%
riboflavin sodium phosphate solution were administered
every minute for a total of 10 minutes until the anterior
donor cornea was briskly colored yellow. The second CXL
session was also performed with a 30-mW/cm2 fluence for
4 minutes until a total of 7.2 mJ/cm2 of energy was reached.
Ultraviolet-A in all cases was administered by using the KXL
crosslinking device (Avedro Inc, Waltham, MA).
The central, 3-mm trephination of the donor cornea
button was performed with a femtosecond laser. Before
mounting the KPro, the donor cornea was trephined on
a disposable Barron donor block (9.00 mm). Then, the KPro
was sutured in place with 16 interrupted 10.0 nylon sutures,
and the wound was deemed watertight. After the surgery, all
cases were fitted with an 18-mm-diameter bandage contact
lens to reduce the friction between the eyelids and the
operated ocular surface. All patients were treated postoperatively with a drop of ofloxacin and 50 mg/mL of a solution of
vancomycin once a day. In the later 6 years, all patients were
treated with amoxifloxacin 4 times a day and with vancomycin as well. In addition, it should be noted that antifungal
prophylaxis, 1 drop of natamycin (Natacyn; Alcon, Ireland),
was administered weekly to all the patients.
All patients were evaluated on the first postoperative day,
every month for 6 months, and every 3 months thereafter to
assess visual acuity and the condition of the external surface.
Because the capability of assessing intraocular pressure was
limited to fingertip application over the eyelids, meticulous
optic nerve visualization every 3 months was used as a means
to evaluate possible glaucomatous optic nerve damage.
This work adhered to the tenets of the Declaration of
Helsinki, and the study received the approval from the Ethics
Committee of our Institution. All patients were provided
a written informed consent before the treatment, and a comprehensive explanation of the benefits and risks of this
procedure was presented to them by the operating surgeon
(A.J.K.).
FIGURE 1. Inner donor cornea CXL through the
femtosecond laser–created pocket. A, FS200 femtosecond laser programming interface. B, Screen capture of the 8-mm diameter, 400-mm-deep
femtosecond laser–assisted pocket creation. C, Intrastromal infusion of 0.1% riboflavin solution with the
olive-tip cannula.
! 2014 Lippincott Williams & Wilkins
915
Kanellopoulos and Asimellis
RESULTS
The mean age of the patients was 67 6 14 years. Six
patients were female and 5 were male. The visual acuity
assessed from preoperative light perception and/or hand
motion showed a 6-month postoperative improvement. The
average UDVA was 20/80 (range: 20/100–20/40), and the
CDVA was 20/70 (range: 20/80–20/32).
These patients are still being followed up. After the first
postoperative year, each patient is evaluated at least annually.
During the long follow-up time that these patients have been
continuously monitored (minimum 1 year, maximum 9 years),
2 of the patients required subsequent injection of intracameral
and triamcinolone and bevacizumab injection (Avastin; Genentech/Roche, San Francisco, CA) because of cystoid macular
edema. Additionally, 1 patient needed yttrium aluminum
garnet laser intervention for a retroprosthesis inflammatory
membrane that was quite dense and had resulted in a CDVA
reduction from 20/60 to 20/400. After this procedure, the
patient’s vision returned to 20/50.
Figure 1 demonstrates the procedure. Figure 1A shows
the FS200 femtosecond laser programming interface. Figure
1B is a screen capture of the 8-mm diameter, 400-mm-deep
femtosecond laser–assisted pocket creation. Figure 1C, is
a screen capture of the intrastromal infusion of 0.1% riboflavin
solution with the olive-tip cannula. Figure 2 illustrates the CXL
of the cornea, the anterior part of the donor cornea after epithelial debridement, and instillation of riboflavin solution. Figure 3 shows the trephination of the crosslinked vehicle donor
cornea in its center to fit the KPro. Figure 4 shows results from
a case 4 years postoperatively. This patient had an explosionrelated injury. The right eye had to be enucleated as a result.
The left eye sustained a chemical injury, which resulted in the
visual acuity being light perception and severe cicatricial
changes occurring in both the conjunctiva and cornea. KPro
was deemed to be the optimal treatment option for this left eye.
The patient’s vision improved from light perception to 20/40
UDVA in the first week postoperatively.
DISCUSSION
In our 20 years of experience in external disease and the
use of the Boston KPro to address it, the main obstacles of
prosthesis and visual rehabilitation stability that we have
encountered and reported (Peralta RJ, Kanellopoulos AJ. Boston
keratoprosthesis: A long-term prospective clinical study A LongTerm Prospective Clinical Study. Poster Presentation, ARVO
Meeting, May 6–10, 2007, Fort Lauderdale, FL) have been intraocular pressure control, infection (which was attributed partly on
cornea melt around the prosthesis), and intraocular inflammation.
One of the 2 major difficulties in managing these
patients has been antibiotic prophylaxis, because these eyes
are especially susceptible to microbial infections,17,18 which,
after the KPro surgery, almost invariably leads to endophthalmitis in a unichamber eye with very poor prognosis.19–22
The second significant postoperative management
problem is donor vehicle cornea and/or host cornea melts,23,24
High-Fluence CXL in Keratoprosthesis
especially near the graft–host interface. Using antiproteolytics, such as oral tetracycline-type medications and/or topical progesterone, may be an effective alternative.16
The decision to incorporate this adjunct prophylactic
treatment in these very challenging cases was based on
significant experience with CXL techniques. The long-term
safety and efficacy results of this technique as noted above
suggest that there may exist a very significant advantage for
the long-term prognosis of the Boston KPro.
This work presents 11 cases treated with adjuvant
crosslinking. The relative rarity of the parameters that led to
the decision for inclusion in this study leads us to believe that
our cases represent 1 of the largest groups in the literature.
Among the reasons for crosslinking was our observation that
up to 50% of these patients suffer from cornea melting, which
may increase their likelihood of developing infections. The
lack of a control group is a significant flaw of this study; in
our defense, the seriousness and urgency for treatment and
our strong belief in the benefit of crosslinking were reasons
why we did not include a control group.
Questions on whether crosslinked corneas allow effective topical antibiotic penetration and/or the apoptosis of
cornea keratocytes,25 which is a side effect of CXL, and their
effect on long-term microbial host defenses, are not answered
in this study. However, they remain important considerations.
There are recent reports indicating that crosslinked corneas do
allow for effective antibiotic penetration within the corneal
stroma,26 and there is a possibility that the donor vehicle
cornea may have reduced antigenicity to the host’s immune
mechanisms after crosslinking, because most of the keratocytes will be killed in the crosslinking process. This has been
shown in basic science studies.27,28 Because we have incorporated this novel pretreatment technique in our KPro routine,
larger-scale future studies may further validate these findings.
In conclusion, the very high-fluence CXL of the donor
vehicle cornea as a prophylaxis against corneal melt and
extreme external disease may be an efficacious adjunct that
helps to reduce the susceptibility of these corneas to
enzymatic digestion and cornea infection.
REFERENCES
FIGURE 2. CXL of the cornea, the anterior part of the donor
cornea after epithelial debridement, and installation of riboflavin solution with very high-fluence CXL. A, The first crosslinking session of the donor cornea through intact epithelium
and riboflavin solution injected in the lamellar pocket with 30
mW/cm2 for 4 minutes. B, Scraping the donor corneal epithelium with a crescent blade before soaking the stromal
surface, in preparation for the second crosslinking session.
C, Soaking the deepithelialized donor cornea with riboflavin
solution as a preparation for the second crosslinking session.
916
FIGURE 3. Donor Cornea after 2.8-mm central trephination
and just before the peripheral 9.5-mm trephination.
FIGURE 4. Four years postoperative anterior-segment OCT
imaging of the patient who had received prophylactic CXL.
Top panel, meridional scan at 90˚, bottom panel top view of
the cornea showing the scan orientation.
1. Cruzat A, Shukla A, Dohlman CH, et al. Wound anatomy after type 1
Boston KPro using oversized back plates. Cornea. 2013;32:1531–1536.
2. Ziai S, Rootman DS, Slomovic AR, et al. Oral buccal mucous membrane
allograft with a corneal lamellar graft for the repair of Boston type 1
keratoprosthesis stromal melts. Cornea. 2013;32:1516–1519.
3. Ciolino JB, Belin MW, Todani A, et al; Boston Keratoprosthesis Type 1
Study Group. Retention of the Boston keratoprosthesis type 1: multicenter study results. Ophthalmology. 2013;120:1195–1200.
4. Klufas MA, Colby KA. The Boston keratoprosthesis. Int Ophthalmol
Clin. 2010;50:161–175.
5. Ngakeng V, Hauck MJ, Price MO, et al. AlphaCor keratoprosthesis:
a novel approach to minimize the risks of long-term postoperative complications. Cornea. 2008;27:905–910.
6. Lim LS, Ang CL, Wong E, et al. Vitreoretinal complications and vitreoretinal surgery in osteo-odonto-keratoprosthesis surgery. Am J Ophthalmol. 2014;157:349–354.
7. Ghaffariyeh A, Honarpisheh N, Karkhaneh A, et al. Fyodorov–Zuev
keratoprosthesis implantation: long-term results in patients with multiple
failed corneal grafts. Graefes Arch Clin Exp Ophthalmol. 2011;249:
93–101.
8. Kanellopoulos AJ. Post-LASIK ectasia. Ophthalmology. 2007;114:1230.
917
Kanellopoulos and Asimellis
9. Kanellopoulos AJ, Pamel GJ. Review of current indications for combined very high fluence collagen cross-linking and laser in situ keratomileusis surgery. Indian J Ophthalmol. 2013;61:430–432.
riboflavin in a femtosecond laser-created pocket: initial clinical results.
J Refract Surg. 2009;25:1034–1037.
11. Krueger RR, Ramos-Esteban JC, Kanellopoulos AJ. Staged intrastromal
delivery of riboflavin with UVA cross-linking in advanced bullous keratopathy: laboratory investigation and first clinical case. J Refract Surg.
2008;24:S730–S736.
12. Kanellopoulos AJ, Asimellis G. Anterior-segment optical coherence
tomography investigation of corneal deturgescence and epithelial remodeling after DSAEK. Cornea. 2014;33:340–348.
13. Sakimoto T, Sawa M. Metalloproteinases in corneal diseases: degradation and processing. Cornea. 2012;31(suppl 1):S50–S56.
14. Robert MC, Moussally K, Harissi-Dagher M. Review of endophthalmitis
following Boston keratoprosthesis type 1. Br J Ophthalmol. 2012;96:
776–780.
15. Palioura S, Kim B, Dohlman CH, et al. The Boston keratoprosthesis type
I in mucous membrane pemphigoid. Cornea. 2013;32:956–961.
16. Kang JJ, Allemann N, Vajaranant T, et al. Anterior segment optical
coherence tomography for the quantitative evaluation of the anterior
segment following Boston keratoprosthesis. PLoS One. 2013;8:e70673.
17. Kim MJ, Yu F, Aldave AJ. Microbial keratitis after Boston type I keratoprosthesis implantation: incidence, organisms, risk factors, and outcomes. Ophthalmology. 2013;120:2209–2216.
18. Robert MC, Eid EP, Saint-Antoine P, et al. Microbial colonization and
antibacterial resistance patterns after Boston type 1 keratoprosthesis.
Ophthalmology. 2013;120:1521–1528.
19. Robert MC, Pomerleau V, Harissi-Dagher M. Complications associated
with Boston keratoprosthesis type 1 and glaucoma drainage devices. Br J
Ophthalmol. 2013;97:573–577.
20. Sivaraman KR, Hou JH, Allemann N, et al. Retroprosthetic membrane
and risk of sterile keratolysis in patients with type I Boston keratoprosthesis. Am J Ophthalmol. 2013;155:814–822.
21. Chan CC, Holland EJ. Infectious keratitis after Boston type 1 keratoprosthesis implantation. Cornea. 2012;31:1128–1134.
22. Utine CA, Tzu JH, Akpek EK. Clinical features and prognosis of Boston
type I keratoprosthesis-associated corneal melt. Ocul Immunol Inflamm.
2011;19:413–418.
23. Feng MT, Burkhart ZN, McKee Y, et al. A technique to rescue keratoprosthesis melts. Cornea. 2013. [epub ahead of print] (PMID:
23974889).
24. Adesina OO, Vickery JA, Ferguson CL, et al. Stromal melting associated
with a cosmetic contact lens over a Boston keratoprosthesis: treatment
with a conjunctival flap. Eye Contact Lens. 2013;39:e4–6.
25. Jordan C, Patel DV, Abeysekera N, et al. In vivo confocal microscopy
analyses of corneal microstructural changes in a prospective study
of collagen cross-linking in keratoconus. Ophthalmology. 2014;121:
469–474.
26. Tayapad JB, Viguilla AQ, Reyes JM. Collagen cross-linking and corneal
infections. Curr Opin Ophthalmol. 2013;24:288–290.
27. Mencucci R, Marini M, Paladini I, et al. Effects of riboflavin/UVA
corneal cross-linking on keratocytes and collagen fibres in human cornea.
Clin Experiment Ophthalmol. 2010;38:49–56.
28. Messmer EM, Meyer P, Herwig MC, et al. Morphological and immunohistochemical changes after corneal cross-linking. Cornea. 2013;32:
111–117.
Novel myopic refractive correction
ZLWKWUDQVHSLWKHOLDOYHU\KLJKÁXHQFHFROODJHQ
cross-linking applied in a customized pattern:
early clinical results of a feasibility study
Anastasios John
Kanellopoulos
LaserVision.gr Institute, Athens,
Greece, and New York Medical School,
New York, NY, USA
Point your SmartPhone at the code above. If you have a
QR code reader the video abstract will appear. Or use:
http://dvpr.es/1eiR39A
Correspondence: A John Kanellopoulos
LaserVision.gr Institute, 17 Tsocha Street,
115 21 Athens, Greece
Tel 30 21 0747 2777
Fax 30 21 0747 2789
Email [email protected]
ORIGINAL RESEARCH
Open Access Full Text Article
Video abstract
918
Dovepress
open access to scientific and medical research
Background: The purpose of this study is to report the safety and efficacy of a new application
of collagen cross-linking using a novel device to achieve predictable refractive myopic changes
in virgin corneas.
Methods: Four cases were treated with a novel device employing very high-fluence collagen
cross-linking applied in a myopic pattern. Prior to treatment, riboflavin solution was applied to
the intact epithelium. The collagen cross-linking device was then engaged for a total of 12 J/cm2,
to be applied transepithelially in a predetermined pattern. Cornea clarity, corneal keratometry,
and corneal topography were evaluated by both Placido disc and Scheimpflug imaging, along
with cornea anterior segment optical coherence tomography and endothelial cell counts.
Results: An average of 2.3 diopters was achieved in the first week in all four cases treated
with the very high-fluence myopic collagen cross-linking intervention. There was a slight
regression to 1.44 diopters at 1 month, which remained stable at 6-month follow-up. The mean
keratometry change was from 44.90 diopters to 43.46 diopters. There was no significant change
in endothelial cell counts or corneal clarity. There was some mild change in epithelial thickness
distribution, with the treated area showing a slight but homogeneous reduction in mean thickness from 52 Mm to 44 Mm.
Conclusion: This report describes the novel application of very high-fluence collagen crosslinking with a predictable well defined myopic refractive (flattening) corneal effect. This
technique has the advantages of essentially no postoperative morbidity, immediate visual
rehabilitation, and the potential for tapering until the desired result is achieved.
Keywords: myopia, refractive correction, high-fluence collagen cross-linking, clinical results
Introduction
Collagen cross-linking has been used for many years as a means of stabilizing cornea
ectasia.1–5 Although a multitude of treatments and techniques are available, it has been
well documented that the procedure almost invariably results in some central anterior
corneal flattening,1–5 which has often been interpreted as “disease regression.” As our
understanding and the technology available for collagen cross-linking has progressed,
it has been theorized that differential application of collagen cross-linking in specific
areas of the cornea may produce predictable refractive changes. Several aspects of
this theory need further investigation. Is it possible to achieve predictable refractive
changes? Can this be achieved through an intact epithelium? Can the human cornea
tolerate higher fluence of ultraviolet light? This paper describes the use of a novel
697
Clinical Ophthalmology 2014:8 697–702
Dovepress
© 2014 Kanellopoulos. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0)
License. The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further
permission from Dove Medical Press Limited, provided the work is properly attributed. Permissions beyond the scope of the License are administered by Dove Medical Press Limited. Information on
how to request permission may be found at: http://www.dovepress.com/permissions.php
http://dx.doi.org/10.2147/OPTH.S59934
Dovepress
Kanellopoulos
device employing very high-fluence collagen cross-linking,
applied with a customizable pattern, in order to achieve
myopic refractive changes.
Materials and methods
The study included four partially sighted volunteers with
vision less than 20/400 (count fingers and worse), due to
end-stage wet age-related macular degeneration, myopic
refraction from 3 to 6 diopters, and astigmatism from
0.25 to 2.5 diopters. None had previously undergone cornea
surgery. All patients signed informed consent forms, and the
study received approval from the ethics committee. All eyes
were imaged using Placido disc corneal topography (Vario
Topolyzer; Oculus, Wetzlar, Germany), Scheimpflug topography (Pentacam®; Oculus), autorefraction and keratometry
(Speedy-K®; Nikon, Tokyo, Japan), and anterior segment
imaging and mapping by spectral domain anterior segment
optical coherence tomography (RtVue-100; Optovue, Irvine,
CA, USA). Given that manifest refractions are extremely challenging in these cases, only autorefraction data are reported.
Corneal endothelial cell counts were evaluated by confocal
microscopy (Robo K; Konan Medical Inc., Hyogo, Japan).
Surgical technique
A “myopic” treatment plan was designed to employ a
4 mm diameter ultraviolet A application that would deliver
30 mW/cm2 of surface fluence on the pupillary aperture by the
KXL II device (Avedro Inc., Waltham, MA, USA) for a total
exposure time of 4 minutes (12.4 J/cm2 of total energy). The
surgical technique involved positioning an eyelid speculum
in a sterile environment after the eyelids had been swabbed
with 5% povidone iodine solution and draped with Tegaderm™ (3M, Neuss, Germany). A series of drops of ParaCel™
(Avedro Inc.), a specially formulated mildly abrasive 0.25%
riboflavin solution, was applied every 30 seconds for 4 minutes, followed immediately by VibeX Xtra™ (Avedro Inc.),
a 0.25% riboflavin solution and normal saline. The latter
was applied again every 30 seconds for 6 minutes, so total
riboflavin application took 10 minutes. The KXL II device
was then placed immediately over the eye, which was kept
open by the lid speculum. Following appropriate alignment
and focusing by the surgeon, the pupillary aperture of each
eye being treated was captured and tracked using the KXL II
device. Application of ultraviolet A was directed at the 4 mm
diameter area centered at the apex of the cornea.
The cornea was moistened once every minute with a drop
of balanced salt solution. After completion of collagen crosslinking, the eyelid speculum was removed and treatment was
started with a combination of antibiotic (Dispersadron-C®;
Alcon, Fort Worth, TX, USA) and corticosteroid (Vigamox®;
Alcon) eye drops for 10 days.
All patients were examined on the first day, after the first
week, and monthly thereafter for 6 months. Visual acuity
assessment, Placido disc topography, Scheimpflug imaging,
and anterior segment optical coherence tomography were
performed at each visit, along with an endothelial cell count
and autorefraction keratometry.
Results
Dovepress
+LJKÁXHQFHFROODJHQFURVVOLQNLQJIRUP\RSLFUHIUDFWLYHFRUUHFWLRQ
Figure 1 3ODFLGRGLVFWRSRJUDSK\IRUSDWLHQWSUHRSHUDWLYHO\OHIWDQGPRQWKVSRVWRSHUDWLYHO\ULJKWGHSLFWLQJWKHVLJQLÀFDQWDQGUHJXODUFHQWUDOFRUQHDOÁDWWHQLQJHIIHFW
epithelial thickness over the treated area (Figure 3). The
average epithelial thickness was 49 Mm preoperatively, which
decreased to 44 Mm at 1 month postoperatively, and then
increased to 48 Mm at 5 months postoperatively.
Discussion
A multitude of reports have established the significant
refractive changes that accompany classic collagen
cross-linking 1–8 utilizing the classic Dresden protocol
(3 mW/cm2 for 30 minutes), as well as collagen crosslinking utilizing higher fluence,9 and even cross-linking
delivered in eyes that have had riboflavin placed within a
femtosecond laser-created pocket or intrastromal corneal
ring segment channels.10,11 Over the years, most clinicians
have referred to this process as “flattening,” which has often
been interpreted as “disease regression.” We have long
The data for preoperative and postoperative keratometry,
flattening at 1 week and 6 months, corneal endothelial cell
counts, and subject age are summarized in Table 1. All eyes
showed significant, predictable, and very regular flattening
over the central cornea. After the first week, a mean flattening of 2.3 diopters was documented by keratometry, Placido
disc topography (Figure 1), and Scheimpflug tomography
(Figure 2). By 1 month, flattening had regressed to a mean
of 1.44 diopters. These values remained stable through to
follow-up at 6 months, establishing stability of the effect.
Anterior segment optical coherence tomography
imaging showed mild epithelial changes, with the treated
area showing a slight but homogeneous reduction in mean
Table 13UHRSHUDWLYHDQGSRVWRSHUDWLYHNHUDWRPHWU\ÁDWWHQLQJDWZHHNDQGNHUDWRPHWULFÁDWWHQLQJUHVXOWVDWPRQWKVDORQJZLWK
corneal endothelial cell counts and age of each subject
Patient 1
Patient 2
Patient 3
Patient 4
Mean
PreK1
(D)
PreK2
(D)
PostK1
(D)
PostK2
(D)
ZÁDW
(D)
PÁDW
(D)
Pre-ECC
(counts/mm2)
Post-ECC
(counts/mm2)
Age
(years)
44.50
44.25
44.80
44.50
44.50
44.75
45.50
45.50
45.50
45.30
42.75
42.75
43.10
43.25
42.96
43.50
44.50
44.10
43.75
43.96
2.25
1.75
2.10
1.90
2.30
1.45
1.25
1.55
1.50
1.44
1,800
1,500
1,650
1,450
1,600
1,800
1,500
1,650
1,550
1,625
72
68
71
73
71.25
Abbreviations:'GLRSWHUV3UH.ÁDWWHVWSUHRSHUDWLYHNHUDWRPHWU\PHULGLDQYDOXH3UH.VWHHSHVWSUHRSHUDWLYHNHUDWRPHWU\PHULGLDQYDOXH3RVW.ÁDWWHVWSRVWRSHUDWLYH
NHUDWRPHWU\PHULGLDQYDOXHDWPRQWKV3RVW.VWHHSHVWSRVWRSHUDWLYHNHUDWRPHWU\PHULGLDQYDOXHDWPRQWKVZÁDWPHDQNHUDWRPHWULFÁDWWHQLQJQRWHGDWZHHN
PÁDWPHDQNHUDWRPHWULFÁDWWHQLQJQRWHGDWPRQWKV3UH(&&SUHRSHUDWLYHHQGRWKHOLDOFHOOFRXQWFHOOVPP23RVW(&&SRVWRSHUDWLYHHQGRWKHOLDOFHOOFRXQWFHOOVPP2);
age, age of each patient studied at the start of the trial.
Figure 2 6FKHLPSÁXJLPDJLQJGDWDIRUSDWLHQWSUHRSHUDWLYHO\OHIWDQGPRQWKVSRVWRSHUDWLYHO\ULJKWGHSLFWLQJWKHVLJQLÀFDQWDQGUHJXODUFHQWUDOFRUQHDOÁDWWHQLQJHIIHFW
Abbreviations: D, diopters; OD, right eye.
698
Dovepress
Dovepress
699
Dovepress
Kanellopoulos
OS
Pachymetry map
S
OS
S
800
800
750
ST
SN
ST
SN
750
700
700
650
650
600
600
550
T
N
T
N
550
500
500
450
450
400
IT
IN
400
IN
IT
350
350
I
I
300 µm
Prev
SN-IT (2–5 mm): 85
Prev
Later
62
Min: 498
541
Min-median: −56
−41
S-I (2–5 mm): 70
Location Y: −1214
Min-max: −115
Epithelium statistics within central 5 mm zone
Prev
Later
35
−89
Prev
Later
50
48
Inferior:
44
47
Min: 38
42
Max:
51
52
Std dev: 3.9
2.5
Superior:
−831
Later
Min-max: −14
−10
Min/max thickness indicated as */+
Min thickness indicated as *
Epithelium map
Exam date: 07/23/2013, SSI =33.7
Exam date: 12/23/2013, SSI =39.2
S
80
300 µm
Epithelium
Pachymetry
Pachymetry statistics within central 5 mm zone
S
80
75
75
70
ST
SN
ST
SN
70
65
65
60
60
55
50
55
T
N
T
N
50
45
45
40
40
35
30
35
IT
IN
IN
IT
25
20 µm
30
25
I
I
20 µm
Figure 3 Anterior segment optical coherence tomography derived preoperatively and 5 months postoperatively showing corneal thickness and epithelial maps of the central
PPRIWKHFRUQHDLQSDWLHQWDOOXQLWVLQPLFURQV>XP@
theorized that this flattening is a refractive effect resulting
from differential cross-linking between different segments
of the cornea, resulting in a dissimilar stiffening effect,
which macroscopically is interpreted as a refractive change.
Our group has reported previously on the use of higherfluence collagen cross-linking as a prophylactic refractive
stability modulator in both myopic and hyperopic laserassisted in situ keratomileusis.12–14 We have also recently
reported impressive refractive changes in astigmatic keratotomy when “flash” collagen cross-linking is applied just
at the incision margins.15
With the research and development of an appropriate
device done by the Avedro team and the ability to perform
700
Dovepress
feasibility studies with the KXL II device, it appears that this
promise holds true. In a population of elderly patients, we
were able to achieve an impressively regular and predictable
central cornea flattening effect, consistent with a correction
of myopia of about 2.5 diopters.
Of note, the initial refractive effect was slightly greater,
appeared to regress between the first week and the first
month, then remained stable thereafter. No cornea clarity or
endothelial cell changes (the noted difference of 25 cells/mm2
may well be attributed to instrumentation-measurement
precision and centration accuracy) were noted in this study
group, despite application of much higher energy than that
used in the “standard” Dresden protocol.16
Dovepress
Although longer follow-up will be necessary to determine
the long-term stability of the present data, these findings are
compelling with regard to the correction of small myopic refractive errors of the cornea without incision or tissue removal in
an excimer-like fashion or other previously described thermal
techniques combined with collagen cross-linking.17
This novel procedure appears to be extremely simple for
both patient and surgeon, and is essentially performed through
intact epithelium. The interim epithelial remodeling in the
first 6 months, when compared with normal eyes,18 appears
to flatten slightly in a homogeneous way (average 8 microns).
It appears to require extremely minor postoperative lifestyle
adjustment on the part of the patient, and essentially no pain
or discomfort occurs, even within the first few hours following the procedure. The topographic changes seen on Placido
and Scheimpflug imaging as well as on anterior segment
optical coherence tomography are compelling evidence of
the specificity and topography-guided precision of the KXL II
device. This application may have greater efficacy in younger
corneas, given that the corneas studied here were from older
patients and possibly less sensitive to collagen cross-linking.
In patients with early keratoconus where stabilization and
correction of myopic refractive error is desired, the potential
advantages of this procedure would be another possible future
application. These cases were specifically chosen for an initial
feasibility study that would establish the safety and possible
efficacy of this procedure. We introduce herein the clinical
use of ultra high fluence transepithelial CXL for refractive
corneal change. The dose-effect relationship of this treatment
is currently under investigation. Minimal patient discomfort
compared to laser refractive surgery makes this procedure a
possible future alternative for lower refractive errors. Hyperopic and toric corrections are novel applications currently
being investigated. The ease of this procedure and the essentially zero associated morbidity it offers may also allow the
possibility of titrating the effect over two or more treatments.
Hyperopic and toric corrections may be other novel applications that could be attempted using this technology.
Conclusion
This paper introduces a novel technique based on refractive
collagen cross-linking on virgin corneas as an alternative
refractive correction technique for mild myopia. In
the follow-up time evaluated, these patients showed an
impressive and stable reduction in their myopia. This pilot
work may represent a landmark study of a potentially revolutionary new refractive procedure.
+LJKÁXHQFHFROODJHQFURVVOLQNLQJIRUP\RSLFUHIUDFWLYHFRUUHFWLRQ
Acknowledgment
The novel concept of refractive CXL named PiXL was
designed and implemented as concept and technology design
by David Muller, PhD.
Disclosure
This work was presented in part at the International Society of
Refractive Surgery subspecialty day, New Orleans, LA, USA,
November 15–17, 2013. The author has no other conflicts of
interest in this work.
References
1. Ghanem RC, Santhiago MR, Berti T, Netto MV, Ghanem VC.
Topographic, corneal wavefront, and refractive outcomes 2 years after
collagen cross-linking for progressive keratoconus. Cornea. 2014;33(1):
43–48.
2. Arora R, Jain P, Goyal JL, Gupta D. Comparative analysis of refractive
and topographic changes in early and advanced keratoconic eyes
undergoing corneal collagen cross-linking. Cornea. August 22, 2013.
[Epub ahead of print.]
3. Hassan Z, Szalai E, Módis L Jr, Berta A, Németh G. Assessment of
corneal topography indices after collagen cross-linking for keratoconus.
Eur J Ophthalmol. 2013;23(5):635–640.
4. Touboul D, Trichet E, Binder PS, Praud D, Seguy C, Colin J.
Comparison of front-surface corneal topography and Bowman membrane specular topography in keratoconus. J Cataract Refract Surg.
2012;38(6):1043–1049.
5. Piñero DP, Alio JL, Klonowski P, Toffaha B. Vectorial astigmatic
changes after corneal collagen cross-linking in keratoconic corneas
previously treated with intracorneal ring segments: a preliminary study.
Eur J Ophthalmol. 2012;22 Suppl 7:S69–S80.
6. Greenstein SA, Fry KL, Hersh PS. Corneal topography indices
after corneal collagen cross-linking for keratoconus and corneal
ectasia: one-year results. J Cataract Refract Surg. 2011;37(7):
1282–1290.
7. Kanellopoulos AJ. Post-LASIK ectasia. Ophthalmology. 2007;
114(6):1230.
8. Hafezi F, Kanellopoulos J, Wiltfang R, Seiler T. Corneal collagen crosslinking with riboflavin and ultraviolet A to treat induced keratectasia
after laser in situ keratomileusis. J Cataract Refract Surg. 2007;33(12):
2035–2040.
9. Kanellopoulos AJ. Long term results of a prospective randomized
bilateral eye comparison trial of higher fluence, shorter duration ultraviolet A radiation, and riboflavin collagen cross linking for progressive
keratoconus. Clin Ophthalmol. 2012;6:97–101.
riboflavin in a femtosecond laser-created pocket: initial clinical results.
J Refract Surg. 2009;25(11):1034–1037.
11. Alió JL, Toffaha BT, Piñero DP, Klonowski P, Javaloy J. Crosslinking in progressive keratoconus using an epithelial debridement
or intrastromal pocket technique after previous corneal ring segment
implantation. J Refract Surg. 2011;27(10):737–743.
12. Kanellopoulos AJ, Pamel GJ. Review of current indications for
combined very high fluence collagen cross-linking and laser in
situ keratomileusis surgery. Indian J Ophthalmol. 2013;61(8):
430–432.
13. Kanellopoulos AJ, Kahn J. Topography-guided hyperopic LASIK with
and without high irradiance collagen cross-linking: initial comparative
clinical findings in a contralateral eye study of 34 consecutive patients.
J Refract Surg. 2012;28(Suppl 11):S837–S840.
Dovepress
701
!"#$%&
LMNOMMOPQA8Q(%6)#$-8LMMRO8LMSM
!"#$%#&'()*(+*,'-%#$*./%'&01*2#/3045&60*#)7*.)&56'(689%6+#/5*:665;%$#6'&0*')*<56#&(/()%-*#)7*=6(--$')>');*:)&56"5)&'()*?($$(@8%A
'(!)!*+,-+(.!%,$
Kanellopoulos
14. Kanellopoulos AJ. Long-term safety and efficacy follow-up of
prophylactic higher fluence collagen cross-linking in high myopic
laser-assisted in situ keratomileusis. Clin Ophthalmol. 2012;6:
1125–1130.
15. Kanellopoulos AJ. Very high fluence collagen cross-linking as a
refractive enhancement of a regressed previous astigmatic keratotomy.
J Refract Surg. 2013;29(7):504–505.
16. Wollensak G, Spörl E, Seiler T.[Treatment of keratoconus by collagen
cross linking]. Ophthalmologe. 2003;100(1):44–49. German.
Dovepress
17. Kanellopoulos AJ. Laboratory evaluation of selective in situ refractive
cornea collagen shrinkage with continuous wave infrared laser combined
with transepithelial collagen cross-linking: a novel refractive procedure.
Clin Ophthalmol. 2012;6:645–652.
18. Kanellopoulos AJ, Asimellis G. In vivo three-dimensional corneal
epithelium imaging in normal eyes by anterior-segment optical coherence tomography: a clinical reference study. Cornea. 2013;32(11):
1493–1498.
!"#$%#&'()*(+*,'-%#$*./%'&01*2#/3045&60*#)7*.)&56'(68*
9%6+#/5*:665;%$#6'&0*')*<56#&(/()%-*#)7*=6(--$')>');*
:)&56"5)&'()*?($$(@8%A*')*BCB*=#-5.)#-&#-'(-*D(3)*<#)5$$(A(%$(-1*,#-'$'>'*E(%-&(%1*F5(6;5*.-'45$$'-
.G9HI.=H
2%6A(-5J!"#!$%&'()$*+)'!&$(,+-!+.,$)/0!.#1%'+-!2+.3/4')1/0!+%5!
+%)'1$#16(,17+.'!$11'*,-+1$)/!$%5$.'(!.#11'-+)$#%!8$)3!9'1+)#.#%,(!
('&'1$)/!$%!+!&'1/!-+1*'!2##-!#7!.-$%$.+--/65$+*%#('5!,%)1'+)'5!
9'1+)#.#%$.!'/'(0!+%5!$%!9'1+)#.#%$.!'/'(!(,:;'.)'5!)#!.1#((6
-$%9$%*!$%)'1&'%)$#%<!
E#&56'#$-*#)7*45&3(7-J!"#)+-!#7!=>=!9'1+)#.#%$.!?@ABC!.+('(!
8'1'! '&+-,+)'5<! D1#,2! E! 8+(! 7#14'5! 71#4! >FG! ,%)1'+)'5!
9'1+)#.#%$.! '/'(0! +%5! *1#,2! H! 71#4! >=I! 9'1+)#.#%$.! '/'(!
(,:;'.)'5!)#!2+1)$+-!%#14+-$J+)$#%!&$+!)#2#*1+23/6*,$5'5!'K.$4'1!
ODVHUDEODWLRQDQGKLJKÀXHQFHFROODJHQFURVVOLQNLQJ$FRQWURO
*1#,2! A! #7! LMI! 3'+-)3/! '/'(! 8+(! '42-#/'5! 7#1! .#42+1$(#%<!
N'! $%&'()$*+)'5! 5$()+%.'! &$(,+-! +.,$)/0! ,%.#11'.)'5! ?OPQEC0!
EHVWVSHFWDFOH FRUUHFWHG &'9$ DQG 6FKHLPSÀXJGHULYHG
9'1+)#4')1/0! 2+.3/4')1/! ?.'%)1+-! .#1%'+-! )3$.9%'((0! AA"!
+%5! )3$%%'()0! "A"C0! +%5! )8#! +%)'1$#16(,17+.'! $11'*,-+1$)/!
$%5$.'(0!)3'!$%5'K!#7!(,17+.'!&+1$+%.'!?RSQC!+%5!)3'!$%5'K!#7!
3'$*3)! 5'.'%)1+)$#%! ?RTPC<! "3'! .#11'-+)$#%(! :')8''%! )3'('!
2+1+4')'1(! "- WRSRJUDSKLF NHUDWRFRQXV FODVVL¿FDWLRQ 7.&
8'1'!$%&'()$*+)'5<
I5-%$&-J.HUDWRPHWU\IRUJURXS$ZDV.ÀDWr!><UV!
P!+%5!@G!?()''2C!IV<=F!r!I<VG!PW!7#1!*1#,2!H!@L!MM<V>!r><FM!
P!+%5!@G!MF<U=!rM<FL!PW!7#1!*1#,2!A0!@L!MG<UX!rL<MI!P!+%5!
@G!MM<LU!rL<UU!P<!Q$(,+-!+.,$)/!7#1!*1#,2!E!8+(!OPQE!V<LG!r
V<LU!+%5!APQE!V<IX!rV<GI!?5'.$4+-C0!7#1!*1#,2!H0!V<IL!rV<GU!
+%5!V<==!r!V<GG0!+%5!7#1!*1#,2!A0!V<UL!rV<>L!+%5!V<U=!r!V<LG<
! A#11'-+)$#%!:')8''%!RSQ!+%5!"@A!?1GC!8+(!7#1!*1#,2!E!V<UI>0!
+%5!7#1!*1#,26H!V<UUF<!A#11'-+)$#%!:')8''%!RTP!+%5!"@A!8+(!
7#1!*1#,2!E!1G!Y!V<=>L0!+%5!7#1!*1#,2!H!V<=VL<!"3'!Z[A!+%+-/($(!
\+1'+! ,%5'1! )3'! .,1&']! 8+(! 7#1! APQE! V<IIV0!"A"! V<IXF0! RSQ!
V<U=F!+%5!RTP!V<UU=<
=()/$%-'()J![,1!(),5/!$%5$.+)'(!)3+)!)3'!)1+5$)$#%+--/!'42-#/'5!
4')1$.(! #7! &$(,+-! +.,$)/! +%5! .#1%'+-! )3$.9%'((! 4+/! %#)! :'!
1#:,()! $%5$.+)#1(! %#1! 21#&$5'! +..,1+)'! +(('((4'%)! #%! '$)3'1!
9'1+)#.#%,(!('&'1$)/!#1!2#()#2'1+)$&'!'&+-,+)$#%<!"8#!+%)'1$#1!
VXUIDFH LUUHJXODULW\ LQGLFHV GHULYHG E\ 6FKHLPSÀXJLPDJLQJ
,69DQG,+'PD\EHPRUHVHQVLWLYHDQGVSHFL¿FWRROV
Publish your work in this journal
Clinical Ophthalmology is an international, peer-reviewed journal
covering all subspecialties within ophthalmology. Key topics include:
Optometry; Visual science; Pharmacology and drug therapy in eye
diseases; Basic Sciences; Primary and Secondary eye care; Patient
Safety and Quality of Care Improvements. This journal is indexed on
Dovepress
PubMed Central and CAS, and is the official journal of The Society of
Clinical Ophthalmology (SCO). The manuscript management system
is completely online and includes a very quick and fair peer-review
system, which is all easy to use. Visit http://www.dovepress.com/
testimonials.php to read real quotes from published authors.
Submit your manuscript here: KWWSZZZGRYHSUHVVFRPFOLQLFDORSKWKDOPRORJ\MRXUQDl
702
26K/'-J 9LVXDO DFXLW\ 6FKHLPSÀXJGHULYHG SDFK\PHWU\ DQG
+%)'1$#16(,17+.'!$11'*,-+1$)/!.#11'-+)$#%!)#!9'1+)#.#%,(!('&'1$)/!
$%!,%)1'+)'5!.+('(!?EC0!)1'+)'5!8$)3!.1#((-$%9$%*!?HC0!+%5!$%!+!
.#%)1#-!*1#,2!?AC!1'&'+-(!)3+)!&$(,+-!+.,$)/!+%5!2+.3/4')1/!5#!
%#)!.#11'-+)'!8'--!8$)3!9'1+)#.#%,(!('&'1$)/<!
<50@(67-J!E)3'%(!^1#)#.#-0!A#4:$%'5!)#2#*1+23/!*,$5'5!^Z@!
DQGKLJKHUÀXHQFH&;/9LVXDOUHKDELOLWDWLRQLQNHUDWRFRQXV
S'&'1$)/! .1$)'1$+0! @'1+)#.#%,(! 21#*1'(($#%0! @'1+)#.#%,(!
FODVVL¿FDWLRQ3HQWDFDP.HUDWRFRQLF6FKHLPSÀXJWRSRPHWULF
$%5$.'(0! Q$(,+-! +.,$)/0! @'1+)#.#%,(0! D1+5$%*! +%)'1$#1! (,17+.'!
^'%)+.+4!$%5$.'(0!@'1+)#.#%,(!E4(-'1!+%5!@1,4'$.3!*1+5$%*0!
A#1%'+-! 2+.3/4')1/0! Z'.'$&'1! #2'1+)$%*! .3+1+.)'1$()$.! Z[A!
+%+-/($(<
T(@*&(*/'&5*&3'-*#6&'/$5J*@+%'--#2#,-#(!E_0!`#,()#,!Q0!E($4'--$(!
D<!a&+-,+)$#%!#7!Q$(,+-!E.,$)/0!^+.3/4')1/!+%5!E%)'1$#16S,17+.'!
R11'*,-+1$)/!$%!@'1+)#.#%,(!+%5!A1#((-$%9$%*!R%)'1&'%)$#%!b#--#86,2!
$%!=>=!A+('(<!_!@'1+)!a.)!A#1!P$(!GVL>WG?>CcXI6LV><
9(%6/5*(+*-%AA(6&J!B$&RQÀLFWRILQWHUHVWB#%'!5'.-+1'5
:UHIVWX=H:VU
!"#$%&'&()*+ ,!-./0+ 1"#23"1+ 4#&5+ %6"+ 7#""8+ 9&#1*+
țİȡĮĲȠİȚįȒȢ FRUQHD țȫȞȠȢ FRQH PHDQLQJ FRQH
*6$:"1+ :#&%#)*2&(0+ 2*+ $+ '&#("$;+ 12*&#1"#0+ 1"42("1+ $*+ $+
QRQLQÀDPPDWRU\GHJHQHUDWLYHD[LDOWKLQQLQJRIDQHFWDWLF
'&#("$<=9LVLRQLVDIIHFWHGE\LQFUHDVHGP\RSLDGXHWRWKH
FRQHSURWUXVLRQDQGLUUHJXODUDVWLJPDWLVPGXHWRVXEVWDQWLDO
FRUQHDODV\PPHWU\
2XUORQJFOLQLFDOH[SHULHQFHZLWKNHUDWRFRQLFVFUHHQLQJ
$(1+#"6$>2;2%$%2&(LQGLFDWHVWKDWQHLWKHUFRUQHDOSDFK\PHWU\
QRUYLVXDODFXLW\XQFRUUHFWHGGLVWDQFHYLVXDODFXLW\8'9$
DQGEHVWVSHFWDFOHFRUUHFWHGGLVWDQFHYLVXDODFXLW\&'9$
'$(+ >"+ #";2$>;"+ 2(12'$%&#*+ &4+ "'%$*2$+ $(1?&#+ 8"#$%&'&()*+
SURJUHVVLRQDVVHVVPHQW@2QHPD\H[SHFWWKDWWKHSUHVHQFH
RI ODUJH DPRXQWV RI FRUQHDO LUUHJXODULWLHV PLJKW KDPSHU
VXI¿FLHQW VSHFWDFOHFRUUHFWLRQ RI YLVXDO DFXLW\ +RZHYHU+
DW OHDVW LQ RXU H[SHULHQFH RIWHQ HQRXJK NHUDWRFRQLF
SDWLHQWV SUHVHQW ZLWK VXUSULVLQJO\ KLJK &'9$ HYHQ QHDU
GHVSLWH VHYHUH WRSRJUDSKLF LUUHJXODULW\ DQGRU
SDFK\PHWULF WKLQQLQJ SUHVHQW 7KLV PDNHV NHUDWRFRQXV
GLDJQRVLV D GLI¿FXOW DQG SRWHQWLDOO\ GDQJHURXV SURFHVV
DV PRVW HDUO\ PDQ\ DGYDQFHG DQG HYHQ VRPH VHYHUH
FDVHV FDQ EH PLVVHG ZLWK WUDGLWLRQDO VFUHHQLQJ PHWKRGV+
:HKDYHDOVRHQFRXQWHUHGFDVHVZLWKSURJUHVVLYHNHUDWRFRQXV
ZLWKQRFOLQLFDOO\VLJQL¿FDQWUHGXFWLRQLQYLVXDODFXLW\
7RWKHEHVWRIRXUNQRZOHGJHWKHVXEMHFWRITXDQWLWDWLYH
FRUUHODWLRQRIYLVXDODFXLW\ZLWKNHUDWRFRQXVJUDGLQJ+6$*+
EHHQUHSRUWHGRQO\LQYHU\IHZSHHUUHYLHZSXEOLFDWLRQV
7KLVVWXG\DLPVWRLQYHVWLJDWHWKHSRVVLEOHFRUUHODWLRQV
RIYLVXDODFXLW\8'9$DQG&'9$FRUQHDOSDFK\PHWU\
DQGVSHFL¿F6FKHLPSÀXJLPDJLQJGHULYHGDQWHULRUVXUIDFH
WRSRJUDSKLFLUUHJXODULW\LQGLFHVZLWKNHUDWRFRQXVVHYHULW\
LQDODUJHSRRORIFOLQLFDOO\GLDJQRVHGNHUDWRFRQLFH\HVDQG
LQDJURXSRINHUDWRFRQLFH\HVVXEMHFWHGWRFURVVOLQNLQJDQG
DQWHULRUVXUIDFHQRUPDOL]DWLRQLQWHUYHQWLRQDQGH[DPLQHWKH
DSSOLFDELOLW\RIWKHVHLQGLFDWRUVLQNHUDWRFRQXVVFUHHQLQJ
Dovepress
!"#$%"&#'("&)*+(,%"&)*(-*.$%&#(/(",0*&"1*2/#&#'/*3(%"$&)*4'0$&0$05*6$7#$89$%:4$/$89$%*;<=>?;@>ABCD:=<>
!"
!"#$%&
!"#$%#$&'$()'*"(+#",--'.'/-'$(,%(#-(
HFWDVLD VHYHULW\ FODVVL¿FDWLRQ DQG FOLQLFDO NHUDWRFRQXV &;/<13<=)!2/76:2;230)/3>)"3/5?717
PDQDJHPHQWIROORZXS
,Q HDFK FDVH FOLQLFDO H[DPLQDWLRQ LQFOXGHG PRQRFXODU
8'9$DQGVXEMHFWLYHUHIUDFWLRQDQG&'9$ZLWKWKHEHVW
!"#$%&"'()"*+)!$#,-+(
VSHFWDFOHUHIUDFWLRQ%RWK8'9$DQG&'9$ZHUHPHDVXUHG
7KLVVWXG\UHFHLYHGDSSURYDOE\WKH(WKLFV&RPPLWWHHRI %&!5)0./%'!'.&(%-%.&0#
RXU,QVWLWXWLRQDGKHUHQWWRWKHWHQHWVRIWKH'HFODUDWLRQRI
6FKHLPSIOXJ LPDJLQJ ZDV SHUIRUPHG ZLWK WKH
+HOVLQNL,QIRUPHGFRQVHQWZDVREWDLQHGIURPHDFKVXEMHFW :DYH/LJKW2FXO\]HU:DYH/LJKW(UODQJHQ*HUPDQ\D
DWWKHWLPHRIWKH¿UVWFOLQLFDOYLVLW
3HQWDFDP2FXOXV2SWLNJHUlWH*PE+:HW]ODU*HUPDQ\
6FKHLPSÀXJURWDWLQJFDPHUD6716"7KHGHYLFHZDVFDOLEUDWHG
./01230)&34567183)9:102:1/
DFFRUGLQJ WR PDQXIDFWXUHU UHFRPPHQGDWLRQV SULRU WR
$ WRWDO RI VHYHQ KXQGUHG WKLUW\ VHYHQ NHUDWRFRQLF XQGHUWDNLQJ WKH PHDVXUHPHQWV 7KH PHDVXUHPHQWV ZHUH
H\HVZHUHHYDOXDWHGHQUROOHGLQWKHVWXG\RYHUWKHFRXUVH REWDLQHG DQG SURFHVVHG YLD WKH ([DPLQDWLRQ 6RIWZDUH!
RIWKHSDVW\HDUV(DFKSDWLHQWHQUROOHGLQWKHVWXG\ZDV 9HUVLRQU7KHGHIDXOWVHWWLQJVRIWZHQW\¿YHLPDJHV
VXEMHFWHGWRDFRPSOHWHRFXODUH[DPLQDWLRQLQFOXGLQJVOLW SHUVLQJOHDFTXLVLWLRQZDVXVHG6FKHLPSÀXJLPDJLQJZDV
FRQGXFWHGLQRUGHUWRSURYLGHDQWHULRUVXUIDFHNHUDWRPHWU\
ODPSELRPLFURVFRS\IRUFOLQLFDOVLJQVRINHUDWRFRQXV
*URXS $ FRQVLVWHG RI XQRSHUDWHG H\HV FOLQLFDOO\ . ÀDW DQG . VWHHS PHULGLDQ UHSRUWHG LQ NHUDWRPHWULF
GLDJQRVHG ZLWK NHUDWRFRQXV 0HDQ DJH RU SDWLHQWV LQ GLRSWHUV'FRUQHDOSDFK\PHWU\7&7WKLQQHVWFRUQHDO
WKLVJURXSDWWKHWLPHRIWKHH[DPLQDWLRQZDVr!"#$! WKLFNQHVV PHDVXUHG LQ ȝP DQG NHUDWRFRQXV$PVOHU WR\HDUVRIDJH,QWKLVµXQRSHUDWHG.&1¶JURXS$ .UXPHLFK FODVVLILFDWLRQ 7KH WRSRJUDSKLF NHUDWRFRQXV
GLIIHUHQWH\HVZHUHHQUROOHGRIZKLFKZHUHULJKW FODVVL¿FDWLRQ 7.& VFDOH ZLWK LQFUHDVLQJ VHYHULW\ ZDV
2' DQG OHIW 26 *HQGHU VSHFL¿FV ZHUH H\HV ± .& .& .& .& .& .& DQG .&
EHORQJLQJWRIHPDOHSDWLHQWVDQGWRPDOHSDWLHQWV
&RUQHDOVXUIDFHLUUHJXODULW\ZDVHYDOXDWHGE\WZRDQWHULRU
,QFOXVLRQFULWHULDZHUHDPLQLPXPDJHRI\HDUVDQG 03+8,')!-./.5)-+%'!%&(%')01!5),03+)(!%&!-9)!')&-+,4!2!55!
FOLQLFDOGLDJQRVLVRINHUDWRFRQXV([FOXVLRQFULWHULDZHUH FRUQHDO ]RQH7KHVH LQGLFHV ZHUH WKH XQLWOHVV LQGH[ RI
V\VWHPLFGLVHDVHDQ\SUHYLRXVFRUQHDOVXUJHU\KLVWRU\RI VXUIDFH YDULDQFH ,69 DQ H[SUHVVLRQ RI FRUQHDO VXUIDFH
FKHPLFDOLQMXU\RUGHOD\HGHSLWKHOLDOKHDOLQJDQGSUHJQDQF\ FXUYDWXUHLUUHJXODULW\H[SUHVVLQJWKHVWDQGDUGGHYLDWLRQRI
RUODFWDWLRQGXULQJWKHVWXG\IRUWKHIHPDOHSDWLHQWV
WKHVDJLWWDOUDGLXVYDOXHVIURPWKHPHDQDQGWKHLQGH[RI
*URXS % $3WUHDWHG ZDV IRUPHG IURP NHUDWRFRQLF KHLJKWGHFHQWUDWLRQ,+'FDOFXODWHGZLWK)RXULHUDQDO\VLV
SDWLHQWVZKRVHH\HVUHFHLYHGDQWHULRUVXUIDFHQRUPDOL]DWLRQ RIFRUQHDOKHLJKWGDWDWRTXDQWLI\WKHGHJUHHRIYHUWLFDOFRQH
E\ SDUWLDO WRSRJUDSK\JXLGHG H[FLPHU DEODWLRQ FRPELQHG ()')&-+,-%.&#27KH GHFHQWUDWLRQ LV FDOFXODWHGRQ D ULQJ RI!
ZLWK KLJKHU IOXHQFH &;/ D SURFHGXUH ZH LQWURGXFHG PPUDGLXV
DQG UHSRUWHG DV WKH $WKHQV 3URWRFRO 7KH VDPH
)RUJURXSV$DQG&PHDVXUHPHQWVIURPWKHPRVWUHFHQW
VXUJHRQ $-. SHUIRUPHG WKH RSHUDWLRQV 0HDQ DJH RU FOLQLFDOYLVLWKDVEHHQLQFOXGHGLQWKHVWXG\)RUJURXS%
SDWLHQWV LQ WKLV JURXS DW WKH PRQWKV SRVWRSHUDWLYH PHDVXUHPHQWVIURPWKHFORVHVWWRWKHRQH\HDUSRVWRSHUDWLYH
H[DPLQDWLRQ ZDV r WR \HDUV ,Q WKLV! :%0%-!;,0!'.&0%()+)(#!
µ$3WUHDWHG.&1¶JURXSGLIIHUHQWH\HVZHUHHQUROOHG
/LQHDU UHJUHVVLRQ DQDO\VLV ZDV SHUIRUPHG WR VHHN
RIZKLFKZHUHULJKW2'DQGOHIW26H\HV SRVVLEOHFRUUHODWLRQV'HVFULSWLYHDQGFRPSDUDWLYHVWDWLVWLFV
EHORQJHGWRIHPDOHSDWLHQWVDQGWRPDOHSDWLHQWV7KH DQDO\VLVRIYDULDQFHEHWZHHQNHUDWRFRQXV7.&VHYHULW\DQG
QRWHGSUHSRQGHUDQFHLQERWKJURXSVWRZDUGPDOHSRSXODWLRQ UHJUHVVLRQDQDO\VLVDQGUHFHLYHURSHUDWLQJFKDUDFWHULVWLFV
LV FRQVLVWHQW ZLWK RXU FOLQLFDO H[SHULHQFH LQ PDOHIHPDOH 52& FXUYH DQDO\VLV ZHUH SHUIRUPHG ZLWK VWDWLVWLFV
%&'%()&')! %&! *)+,-.'.&%'! /,-%)&-01 2 ! ,&(! *)+,-.'.&30! WRROV SURYLGHG E\ 0LQLWDE YHUVLRQ 0LQL7DE /WG
LQFLGHQFH ODUJH VWXGLHV ,QFOXVLRQ FULWHULD IRU JURXS % &RYHQWU\8.DQG,%063666WDWLVWLFVYHUVLRQ,%0
ZHUHXQHYHQWIXO$WKHQVSURWRFROUHKDELOLWDWLRQDQGQRRWKHU <.+/.+,-%.&1!=);!>.+*1!=>?#!
.'34,+!'.5/4%',-%.&0#!
7KHFRQWUROJURXS&Q GLIIHUHQWH\HVULJKW %$(@'#(
DQGOHIWEHORQJLQJWRPDOHDQGWRIHPDOHSDWLHQWV
A2:/08;20:14=)#8B8;20:14=)./4C?;20:14)/3>)D176/5)
FRQVLVWHGRIXQRSHUDWHGQRUPDOH\HVZLWKQRFXUUHQWRUSDVW
"4610?)%276507
RFXODU SDWKRORJ\ RWKHU WKDQ UHIUDFWLYH HUURU QR SUHYLRXV
VXUJHU\ DQG QR SUHVHQW LUULWDWLRQ RU GU\ H\H GLVRUGHU DOO $V VKRZQ LQ 7DEOH DYHUDJH NHUDWRPHWU\ IRU JURXS$
FRQ¿UPHGE\DFRPSOHWHRSKWKDOPRORJLFHYDOXDWLRQ&RQWDFW XQRSHUDWHG.&1.ÀDWZDVr'DQG.
VWHHS"!r')RUJURXS%$3WUHDWHG.ZDV
OHQVZHDUHUVZHUHH[FOXGHGIURPWKLVJURXS&
!"
!"#$%#&'()*(+*,'-%#$*./%'&01*2#/3045&60*#)7*.)&56'(689%6+#/5*:665;%$#6'&0*')*<56#&(/()%-*#)7*=6(--$')>');*:)&56"5)&'()*?($$(@8%A
7DEOH!"#$%&#'()*%+,%$,(,#"-%*-.+(/0*(1#"2'(3%4-353(/6%42(%+,(3-+-353(/6-+2(%+*#$-.$(7.$+#%8()5$9%7#(:#$%*.3#*$;'(
*.<.3#*$;'(<%7=;3#*$;'(%+,("-)5%8(%75-*;'(9.$(*>.(&$.5<)(-+(*=#()*5,;
*
<56#&(45&60
B(A(45&60
2#/3045&60
,'-%#$*#/%'&0
*
.ÀDW
.VWHHS
:9,
:CD
B=B
ED,.
=D,.
E)'&D
D
8
8
ȝP
D5/'4#$
D5/'4#$
*URXS$XQRSHUDWHG.&1H\HV
!"#$%&#
?@A@B
CDAB@
EEA@
DADEF
???A@?
DAGH
DACE
0*(1#"
IFAJD
ICADH
I?FAHJ
IDADCH
IFBAG?
IDAGJ
IDAHC
6%4
CJAF
@CA@C
HGJ
DAHBC
CHJ
DAE?
GAHH
6-+
FEAC
?HAGB
GB
DADD@
HEB
D
DADB
*URXS%$3WUHDWHG.&1H\HV
!"#$%&#
??ADF
?@AJB
BEAHG
DADCE
F@?AEG
DACG
DABB
0*(1#"
IFA@?
I?A@G
IF@ACJ
IDADFB
I@GACG
IDAHJ
IDAHH
6%4
CCAC
@HABC
GED
DAHDJ
CDG
GAHC
GAHC
6-+
F@AH
FEAE
GG
DADDG
GBE
DADG
DAG
*URXS&FRQWURO
!"#$%&#
?HAJE
??AGJ
FGAJF
DADHF
CHCAGC
DAJG
DAJB
0*(1#"
IGA?C
IGAJJ
IHFA?F
IDADG@
IHBAEF
IDAFG
IDAGH
6%4
?JAB
?BAH
FB
DADFB
CBC
GAFC
GAFC
6-+
?DAF
FEAG
G?
DADDG
??E
DAG
DAB?
1K(,-.<*#$)L(M0NK(-+,#4(.9()5$9%7#("%$-%+7#L(MO1K(-+,#4(.9(=#-&=*(,#7#+*$%*-.+L(PQPK(*=-++#)*(7.$+#%8(*=-7:+#))L(R1N!K(5+7.$$#7*#,(
,-)*%+7#("-)5%8(%75-*;L(Q1N!K(S#)*T)<#7*%78#(7.$$#7*#,(,-)*%+7#("-)5%8(%75-*;
r'DQG.r'DQGIRUJURXS&.
ZDVr'DQG.ZDVr'
2XUDQDO\VLVLQGLFDWHGWKDWPRUHWKDQRIWKHVDPSOH
SRSXODWLRQLQJURXS$XQRSHUDWHG.&1H\HVKDGDVWHHS
PHULGLDQNHUDWRPHWU\!'FRQVLVWHQWZLWKWKH&/(.
JURXSVWDQGDUGV!"
&RUQHDOVXUIDFHLUUHJXODULW\DVH[SUHVVHGE\WKHLQGLFHV
,69DQG,+'ZDVIRUJURXS$,69rDQG,+'
rIRU JURXS % ,69 r DQG ,+'
#$#%&rDQGIRUJURXS&,69rDQG,+'
r#$!&$
$YHUDJHWKLQQHVWFRUQHDOSDFK\PHWU\IRUJURXS$ZDV
rȝPIRUJURXS%rȝPDQGIRU
JURXS&rȝP
9LVXDO DFXLW\ DV UHSRUWHG E\ WKH GHFLPDO H[SUHVVLRQV
RI 8'9$ DQG &'9$ ZDV IRU JURXS$ r #$!'" ()*"
#$%&rIRUJURXS%rDQGr#$++"()*",-."
JURXS&rDQGr#$!+$
!"#$%&'&()*+,"-"#.%/+0#$1.(2
/LQHDU¿WEHWZHHQ9LVXDO$FXLW\7KLQQHVW
3$'4/5"%#/6+7&8&5"%#.'+9(1.'"*+$(1+7!:+0#$1.(2
7KHOLQHDU¿WEHWZHHQWKHYDULRXVSDUDPHWHUVVWXGLHG8'9$
&'9$7&7,69DQG,+'DQGWKH6FKHLPSÀXJGHULYHG
7.&FODVVL¿FDWLRQLVSUHVHQWHGLQWKHIRUPRIPDUJLQDOSORWV
)LJVWRDQGWKHFRHI¿FLHQWVRIGHWHUPLQDWLRQU+/"(.0"
UHSRUWHGLQ7DEOH
)LJXUH LOOXVWUDWHV 8'9$ !" 7.& JUDGLQJ IRU ERWK
JURXSV DQG )LJXUH &'9$ !" 7.& JUDGLQJ IRU ERWK
JURXSV%DVHGRQWKHVHJUDSKVDQGDVUHSRUWHGLQ7DEOH
WKHFRHI¿FLHQWRIGHWHUPLQDWLRQU+ZDVIRUWKHJURXS$
EHWZHHQ8'9$DQG7.&DQGEHWZHHQ&'9$DQG
7.& /LNHZLVH IRU WKH JURXS % EHWZHHQ 8'9$
DQG7.&U+ZDVDQGEHWZHHQ&'9$DQG7.&
7KHOLQHDU¿WEHWZHHQWKLQQHVWFRUQHD7&7DQG7.&
JUDGLQJ LV SUHVHQWHG LQ )LJXUH IRU ERWK JURXSV %DVHG
RQ WKHVH JUDSKV WKH FRHIILFLHQW RI GHWHUPLQDWLRQ U+/"
EHWZHHQ7&7DQG7.&ZDVIRUJURXS$DQGIRU"
JURXS%
7KHOLQHDU¿WEHWZHHQWKHDQWHULRUVXUIDFHLQGLFHV,69
DQG,+'DQG7.&JUDGLQJLVSUHVHQWHGLQ)LJXUHVDQG"
%DVHG RQ WKHVH JUDSKV WKH FRHI¿FLHQW RI GHWHUPLQDWLRQ
1.+EHWZHHQ,69DQG7.&ZDVIRUJURXS$DQGIRU
JURXS%/LNHZLVHWKHFRHI¿FLHQWRIGHWHUPLQDWLRQ
1.+EHWZHHQ,+'DQG7.&ZDVIRUJURXS$DQGIRU
JURXS%UHVSHFWLYHO\
7KHKLVWRJUDPVEDVHGRQWKH6FKHLPSÀXJVHYHULW\JUDGLQJ
RIHDFKH\HLQVHYHQDOSKDQXPHULF7.&JUDGHVIRUJURXSV
$DQG%DUHSUHVHQWHGLQ)LJXUH7RIDFLOLWDWHVWDWLVWLFDO
DQDO\VLVZHLQWURGXFHGDQXPHULFFRQYHUVLRQWKDWLVJUDGH
±ZDVVHWWR.&WR.&WR.&WR.&
WR.&WR.&WRDQG.&WR%DVHGRQWKLV
FRQYHUVLRQIRUJURXS$DYHUDJH7.&JUDGHZDVr!$&%"
WKH DYHUDJH ZDV EHWZHHQ .& DQG .& FORVHU WR WKH
;"'".-"#+<8"#$%.(2+:4$#$'%"#.*%.'+:)#-"+=($>/*.*
.& JUDGH DQG IRU JURXS % DYHUDJH7.& JUDGH ZDV
rFORVHUWRWKH.&JUDGH*URXS&FRPSULVHG 5HFHLYHU RSHUDWLQJ FKDUDFWHULVWLFV 52& FXUYH DQDO\VLV
DUHD XQGHU FXUYH DUHD VWDQGDUG HUURU 6WG HUURU
RIKHDOWK\QRQNHUDWRFRQLFH\HVKDGDYHUDJH7.&±
!"#$%"&#'("&)*+(,%"&)*(-*.$%&#(/(",0*&"1*2/#&#'/*3(%"$&)*4'0$&0$05*6$7#$89$%:4$/$89$%*;<=>?;@>ABCD:=<>
!"
!"#$%&
!"#$%#$&'$()'*"(+#",--'.'/-'$(,%(#-(
!"#$%#&'()*(+*,'-%#$*./%'&01*2#/3045&60*#)7*.)&56'(689%6+#/5*:665;%$#6'&0*')*<56#&(/()%-*#)7*=6(--$')>');*:)&56"5)&'()*?($$(@8%A
!"#$%&'+LVWRJUDPVRINHUDWRFRQXVFODVVL¿FDWLRQIRUWKHWZRJURXSVXQGHUVWXG\/HIW²JURXS$XQRSHUDWHG.&1H\HV&
DQGULJKW²JURXS%$WKHQVSURWRFRO$3WUHDWHG.&1H\HV
!"#$%&'!"#$%&'#(!)(*+!*,!-./0!123)$24425!526&7#((89!#'5!:;-!%$#5&'%!<&+=!*>2$(8&'%!?*3!)(*+4!4=*<&'%!72#'!(2>2(4!#'5!*@+(&2$4A!
/HIW²JURXS$XQRSHUDWHG.&1H\HVDQGULJKW²JURXS%0+=2'4B)$*+*6*(!10C9!+$2#+25!;-D!2824
7DEOH&RHI¿FLHQWRIGHWHUPLQDWLRQU!DQGSHDUVRQFRUUHODWLRQFRHI¿FLHQWIRUWKHWZRJURXSVLQWKHVWXG\EHWZHHQ8'9$DQG
"#$%&$'()&*+,&"#$%&"$"&*+,&"#$%&-.(&"#$%&-/'&*+,&"#$
&RHI¿FLHQWRIGHWHUPLQDWLRQU0
3HDUVRQFRUUHODWLRQFRHI¿FLHQW
01234&)%&3+2451*65,&#$7&5859
:;:<=
>&!;?@=
01234&A%&)BC615*65,&#$7&5859
:;!D@
>&@;@D<
01234&)%&3+2451*65,&#$7&5859
:;!?!
>&E;!FG
01234&A%&)BC615*65,&#$7&5859
:;=<G
>&@;GE?
01234&)%&3+2451*65,&#$7&5859
:;!@D
>&:;:!EG
01234&A%&)BC615*65,&#$7&5859
:;=<D
>&:;:=@=
01234&)%&3+2451*65,&#$7&5859
:;FG@
:;:E=G
01234&A%&)BC615*65,&#$7&5859
:;FFD
:;:EFG
01234&)%&3+2451*65,&#$7&5859
:;<@=
@=;?
01234&A%&)BC615*65,&#$7&5859
:;<:=
E@;=
123!(4$(5+6
623!(4$(5+6
565(4$(5+6
783(4$(5+6
792(4$(5+6
!"#$%('0DUJLQDOSORWRI7&7WKLQQHVWFRUQHDOWKLFNQHVVH[SUHVVHGLQȝPDQG7.&JUDGLQJZLWKRYHUO\LQJER[SORWVVKRZLQJPHDQ
OHYHOVDQGRXWOLHUV/HIW²JURXS$XQRSHUDWHG.&1H\HVDQGULJKW²JURXS%0+=2'4B)$*+*6*(!10C9!+$2#+25!;-D!2824
.&1NHUDWRFRQXV8'9$XQFRUUHFWHGGLVWDQFHYLVXDODFXLW\GHFLPDO7.&WRSRJUDSKLFNHUDWRFRQXVFODVVL¿FDWLRQ&'9$EHVW
VSHFWDFOHFRUUHFWHGGLVWDQFHYLVXDODFXLW\XQLWVGHFLPDO7&7WKLQQHVWFRUQHDOWKLFNQHVVXQLWVȝP,69LQGH[RIVXUIDFHYDULDQFH
-/'H&I+,5J&2K&L5IML6&,5N5+61*6I2+O&)BH&)6L5+9C41262N2P
!"#$%('&Q*1MI+*P&4P26&2K&R'()&S5J415995,&,5NIT*PP8U&*+,&"#$&M1*,I+M&VI6L&2W51P8I+M&X2J&4P269&9L2VI+M&T5*+&P5W5P9&*+,&236PI519;&
/HIW²JURXS$XQRSHUDWHG.&1H\HVDQGULJKW²JURXS%)6L5+9C41262N2P&S)BU&615*65,&#$7&5859
!"
!"#$%)'!"#$%&'#(!)(*+!*,!EF/G!&'523!*,!4@$,#62!>#$&#'62G!#'5!:;-!%$#5&'%!<&+=!*>2$(8&'%!?*3!)(*+4!4=*<&'%!72#'!(2>2(4!#'5!*@+(&2$4!
/HIW²JURXS$XQRSHUDWHG.&1H\HVDQGULJKW²JURXS%0+=2'4B)$*+*6*(!10C9!+$2#+25!;-D!2824
!"#$%"&#'("&)*+(,%"&)*(-*.$%&#(/(",0*&"1*2/#&#'/*3(%"$&)*4'0$&0$05*6$7#$89$%:4$/$89$%*;<=>?;@>ABCD:=<>
!!
!"#$%&
!"#$%#$&'$()'*"(+#",--'.'/-'$(,%(#-(
!"#$%#&'()*(+*,'-%#$*./%'&01*2#/3045&60*#)7*.)&56'(689%6+#/5*:665;%$#6'&0*')*<56#&(/()%-*#)7*=6(--$')>');*:)&56"5)&'()*?($$(@8%A
!"#$%&'!"#$%&'#(!)(*+!*,!-./0!&'123!*,!42&%4+!1252'+$#+&*'0!#'1!678!%$#1&'%!9&+4!*:2$(;&'%!<*3!)(*+=!=4*9&'%!>2#'!(2:2(=!#'1!*?+(&2$=@!
/HIW²JURXS$XQRSHUDWHG.&1H\HVDQGULJKW²JURXS%A+42'=B)$*+*5*(!CADE!+$2#+21!78F!2;2=!
7DEOHG252&:2$!*)2$#+&'%!54#$#5+2$&=+&5=!CGH8E!5?$:2!#'#(;=&=0!#$2#!?'12$!5?$:20!=+#'1#$1!2$$*$0!#=;>)+*+&5!
VLJQDWXUHDQGFRQ¿GHQFHLQWHUYDOUHVXOWV
!0,#(/"1,0(
2/03,
4%15(,00'0(#
!$67.%'%&2(
$&8"#%/0,(9
:';,0(9'/"1
<..,0(9'/"1
8/IA
J@KKJ
J@JLM
J@JJJ
J@KNO
J@PQQ
686
J@KMP
J@JQJ
J@JJM
J@KLK
J@PNR
-SI
J@TQP
J@JLK
J@JJJ
J@TJT
J@MOO
-./
J@TTQ
J@JLP
J@JJJ
J@TRQ
J@MKQ
7HVWUHVXOWYDULDEOHV
$V\PSWRWLFFRQ¿GHQFHLQWHUYDO
8/IAU!<2=+B=)25+#5(2!5*$$25+21!1&=+#'52!:&=?#(!#5?&+;V!686U!+4&''2=+!5*$'2#(!+4&5W'2==V!-SIU!&'123!*,!=?$,#52!:#$&#'52V!-./U!&'123!*,!
42&%4+!1252'+$#+&*'V!='%,$U!C#E!X'12$!+42!'*')#$#>2+$&5!#==?>)+&*'!C<E!F?((!4;)*+42=&=U!+$?2!#$2#!Y!J@K
()*+,**)-.
!"#$%/'!G252&:2$!*)2$#+&'%!54#$#5+2$&=+&5=!)(*+!,*$!+42!,*?$!:#$&#<(2=0!
8/IA0! 6860! -SI! #'1! -./@! C8/IAU! <2=+B=)25+#5(2! 5*$$25+21!
1&=+#'52!:&=?#(!#5?&+;V!686U!+4&''2=+!5*$'2#(!+4&5W'2==V!-SIU!&'123!
*,!=?$,#52!:#$&#'52V!-./U!&'123!*,!42&%4+!1252'+$#+&*'E
DV\PSWRWLFVLJQDWXUHDQG FRQ¿GHQFHLQWHUYDOUHVXOWV
DUHUHSRUWHGLQ7DEOHDOVRSORWWHGLQ)LJXUHIRUWKH
IROORZLQJSDUDPHWHUV&'9$7.&,69DQG,+'%DVHG
RQWKLVDQDO\VLVWKHµDUHDXQGHUWKHVHQVLWLYLW\!"#VSHFL¿FLW\
FXUYH¶ZDVIRU&'9$IRU7&7IRU,69
DQGIRU,+'
!""
7KHUHKDYHEHHQVHYHUDOUHSRUWVLQWKHSHHUUHYLHZOLWHUDWXUH
ODWHO\UHJDUGLQJWKHNHUDWHFWDVLDDQGNHUDWRFRQXVDVVHVVPHQW!
DQG SURJUHVVLRQ PRQLWRULQJ"#$"%! &'! ()**! &'! +,'-,+).&-/0)!
IROORZXSGXHWRYDULRXV&;/LQWHUYHQWLRQV127KHFXUUHQW
RSWLRQV RI WKH FOLQLFDO LQYHVWLJDWRU LQFOXGH TXDQWLWDWLYH
HYDOXDWLRQ RI FRUQHDO PRUSKRORJLF SDUDPHWHUV1"! 3)./0)3!
IURP WRSRJUDSK\ RU 6FKHLPSIOXJ WRSRPHWU\ !
7KH ODWWHU PRGDOLW\ SURYLGHV VSHFLILF DQWHULRUVXUIDFH
FRUQHDOLUUHJXODULW\LQGLFHVGHYHORSHGIRUWKHJUDGLQJDQG
FODVVL¿FDWLRQRINHUDWRFRQXVVWDJHV
7KH DVVRFLDWLRQ RI YLVXDO SHUIRUPDQFH IURP RSWLFDO
TXDOLW\PHWULFVKDVEHHQLQYHVWLJDWHGLQOHQJWKIRUQRUPDO
H\HV DQG LQ KLJKO\ DEHUUDWHG H\HV ZLWK NHUDWRFRQXV!
9LVXDO DFXLW\ ZKLFK LV FRPPRQO\ PHDVXUHG LQ PHVRSLF
FRQGLWLRQVSURYLGHVDKLJKFRQWUDVWIRUFHGFKRLFHWHVWIRU
HVWDEOLVKLQJWKUHVKROGYDOXHVRIYLVXDOSHUIRUPDQFHDQGLW
LV KLJKO\ VHQVLWLYH WR GLVWXUEDQFHV LQ WKH YLVXDO SDWKZD\
SUHVHQWLQJFKDOOHQJHVLQWKHTXDQWL¿FDWLRQ
7RWKHEHVWRIRXUNQRZOHGJHZHLGHQWL¿HGRQO\WZR
UHSRUWVLQWKLVPDWWHURIFRUUHODWLRQRIWKHDERYH6FKHLPSÀXJ
3)./0)3!/43/5)'!(/-6!)/-6).!7)'-!'+)5-&5*)!5,..)5-)3!3/'-&45)!
!"#$%&'%FXLW\&'9$(RUZLWKWKHVHYHULW\RINHUDWRFRQXV
FODVVL¿FDWLRQ
7KH DVVHVVPHQW RI NHUDWRFRQXV VHYHULW\ ZLWK YLVXDO
IXQFWLRQ KDV \LHOGHG SRRU UHVXOWV LQ D QXPEHU RI IURQW
VXUIDFHGHULYHG SDUDPHWHUV LQ NHUDWRFRQLF H\HV $V
")*"+%,-*'")'.-#$&,#'/.-#-),-*'")0(IRUH[DPSOHWKHDYHUDJH
FRUUHODWLRQFRHI¿FLHQWVUDPRQJ&'9$DQGNHUDWRPHWULF
DQGDQWHULRUVXUIDFHLUUHJXODULW\SDUDPHWHUVZHUHEHWZHHQ
DQGZKLFKLQWXUQWUDQVODWHWRFRHI¿FLHQWVRI
*-,-.1")%,"2)'3.4DQG$VQRWHGLQRXUUHVXOWV
WKHVSUHDGRI&'9$PHDVXUHPHQWVZLWKLQWKHVDPHµVHYHULW\
VWDJH¶HJ.&.&ZDVIRXQGWREHWRRODUJH7KHORZHU
WLHUDVZHOODVWKHXSSHUHQGRIHLWKHU8'9$RU&'9$YDOXHV
ZHUHÀXFWXDWLQJLQVHYHUDOVWDJHVRI7.&IURPPRGHUDWH
HJ.&RUORZHUWRVHYHUHHJ.&RUKLJKHUWKHUHIRUH
ODFNLQJWKHFRQWLQXXPRIPHDVXUHPHQWVQHHGHGWRSURYLGHD
VPRRWKJUDGDWLRQRIWKHFRQGLWLRQIURPORZWRVHYHUHVWDJH
7KH FRUUHODWLRQ EHWZHHQ &'9$ DQG 7.& 7DEOH KDG
FRHI¿FLHQWVRIGHWHUPLQDWLRQIRUWKHXQRSHUDWHG.&1
H\HVDQGIRUWKH$3WUHDWHG.&1H\HV7KHFRUUHODWLRQ
EHWZHHQ7&7DQG7.&ZDVDOVRSRRUU4 IRUWKH
XQWUHDWHG.&1JURXS$DQGIRUWKH$3WUHDWHG.&1
JURXS % 7KHVH ORZ FRHI¿FLHQW RI GHWHUPLQDWLRQ YDOXHV
LQGLFDWHWKDWYLVXDODFXLW\DQGRUFRUQHDOSDFK\PHWU\PD\
QRWEHDGHSHQGDEOHLQGLFDWRURINHUDWRFRQXVVHYHULW\DQG
RUSURJUHVVLRQ
7KHUHDUHPDQ\SRVVLEOHUHDVRQVWKDWPD\H[SODLQZK\
!"#$%&' /-.52.1%)+-' "#' )2,' 6-&&' +2..-&%,-*' ,2' 7-.%,2+2)$#8'
7KHODUJHQRWHGÀXFWXDWLRQRIYLVXDOSHUIRUPDQFHLVSDUWO\
GHWHUPLQHGE\IDFWRUVXQUHODWHGWRFRUQHDOVKDSHVXFKDVWHDU
¿OPEUHDNXSOHQWLFXODUVKDSHDQGRSDFLWLHVDQGQHXURORJLFDO
IDFWRUVSRVVLEOHDGYDQFHGQHXUDOSURFHVVLQJGHYHORSPHQWLQ
WKHLQGLYLGXDO7KHHIIHFWVRIRSWLFDODEHUUDWLRQVRQLPDJH
IRUPDWLRQDUHDOVRYHU\FRPSOH[$VRIWNHUDWRFRQLFFRUQHD
PD\GLVSOD\µPXOWLIRFDOLW\¶LHWKHFRUQHDPD\EHDGDSWDEOH
ZKLFKPD\IXUWKHUDGGYDULDELOLW\LQWKHPHDVXUHGYLVXDO
DFXLW\$GGLWLRQDOO\ VLPSOH FOLQLFDO UHDVRQV PD\ H[LVW DV
6-&&0'#$+9'%#',9-'5%+,',9%,'")'+&")"+%&'-!%&$%,"2)'6-'.-5.%+,'
WKHVH\RXQJSDWLHQWVPRQRFXODUO\DQGWKXVDOORZWKHPWR
WLOWWKHLUKHDGLQPDQ\GLUHFWLRQVLQRUGHUWREHQH¿WIURP
WKHFRUQHDPXOWLIRFDOLW\XVHVLJQL¿FDQWDFFRPPRGDWLRQDQG
SLQKROLQJDQGZHOODVVTXLQWLQJ
/LNHZLVHFRUQHDOWKLFNQHVVKDVEHHQVXJJHVWHGLQRXU
ZRUNDVDSRRULQGLFDWRURINHUDWRFRQXVVHYHULW\$OWKRXJK
LW LV WUXH WKDW NHUDWRFRQXV LV D WKLQQLQJ GLVHDVH DQ\
LQGLYLGXDOWKLFNQHVVKDVODUJHYDULDQFHDQGSRRUVHQVLWLYLW\
WRGLVWLQJXLVKNHUDWRFRQXVIURPQRUPDOFRUQHDV
7KHGDWDSURYLGHGKHUHLQVXJJHVWWKDWFOLQLFDODVVHVVPHQW
RINHUDWRFRQXVVHYHULW\DQGRUSURJUHVVLRQEDVHGRQYLVXDO
DFXLW\DQGRUWKLQQHVWSDFK\PHWU\DORQHPD\EHPLVOHDGLQJ
0RUHRYHU WKH SRRU FRUUHODWLRQ IRXQG LQ WKH$3WUHDW-*'
JURXS%LQGLFDWHVWKDWYLVXDODFXLW\DQGFRUQHDOWKLFNQHVV
DOVRFDQQRWEHHPSOR\HGDVVSHFL¿FGLVHDVHVWDJLQJPDUNHUV
LQWKHSRVWRSHUDWLYHDVVHVVPHQWRILQWHUYHQWLRQVDLPLQJWR
DUUHVW WKH NHUDWRFRQXV SURJUHVVLRQ VXFK DV FURVVOLQNLQJ
ZLWK ULERÀDYLQ &;/ 7KH SRVVLEOH DGYDQWDJHV RI D
FRUQHD µPXOWLIRFDOLW\¶ DQG µDGDSWDWLRQ¶ LQ DQ XQWUHDWHG
NHUDWRFRQLFH\HDUHWRDODUJHGHJUHHFRPSURPLVHGZLWKD
&;/SURFHGXUHVLQFHWKHFRUQHDEHFRPHVVWLIIHU
,QWKLVH[WUHPHO\ODUJHVDPSOHRISDWLHQWVHYDOXDWHGWKH
FRPSHOOLQJ GLVHDVH VWDJLQJ PDUNHUV DSSHDU WR EH WKH WZR
DQWHULRU VXUIDFH LUUHJXODULW\ LQGLFHV QDPHO\ WKH ,69 DQG
WKH,+'7KLVZRUNHVWDEOLVKHVWKDWDEHWWHUDSSURDFKPD\
EH WKH H[DPLQDWLRQ RI TXDQWLWDWLYH LQGLFDWRUV WKDW UHÀHFW
WKH DQWHULRUVXUIDFH YDULDQFH DFURVV WKH FRUQHD 7KHVH
DQWHULRUVKDSHEDVHGLQGLFHVSURYLGHSRVLWLYHUHVXOWVDQG
SURYLGHDTXDQWLWDWLYHWRROIRUNHUDWRFRQXVFODVVL¿FDWLRQDQG
SURJUHVVLRQDVVHVVPHQW6SHFL¿FDOO\WKHDYHUDJHFRHI¿FLHQW
25'*-,-.1")%,"2)'3.4DVUHSRUWHGLQ7DEOHEHWZHHQ,69
DQGWKHGHWHUPLQHG7.&NHUDWRFRQXVVHYHULW\JUDGHKDGDQ
DYHUDJHRIIRUERWKNHUDWRFRQLFJURXSVDQGEHWZHHQ
,+'DQG7.&UHVSHFWLYHO\,QRWKHUZRUGVRXUVWXG\
LQGLFDWHV WKDW WKHUH LV D VLJQL¿FDQW FRUUHODWLRQ 7DEOH '
)LJVDQGEHWZHHQWKHWZRDQWHULRUVXUIDFHLUUHJXODULW\
LQGLFHVDQGNHUDWRFRQXVFODVVL¿FDWLRQZKLFKLVZLWKLQWKH
VDPHPDUJLQVHLWKHUWKHXQWUHDWHGNHUDWRFRQLFJURXS$DQG
WKH$3WUHDWHGJURXS%
7KHVH ¿QGLQJV DUH DOVR TXDQWLWDWLYHO\ VXSSRUWHG E\
WKH UHFHLYHU RSHUDWLQJ FKDUDFWHULVWLFV 52& DQDO\VLV
6SHFL¿FDOO\ WKH DUHD XQGHU WKH FXUYH LQGLFDWLYH RI WKH
VHQVLWLYLW\RIWKHLQGH[XQGHUVWXG\DVUHSRUWHGLQ7DEOH'
ZDVIRXQGWREHIRUWKH&'9$IRUWKH7&7DQG
VXEVWDQWLDOO\ ODUJHU IRU WKH ,69 DQG ,+' LQGLFHV ZKRVH
UHVSHFWLYH YDOXHV ZHUH DQG LQGLFDWLQJ WKDW
,69DQG,+'DUHPRUHVHQVLWLYHLQGLFDWRUVIRUNHUDWRFRQXV
VHYHULW\FODVVL¿FDWLRQ,QFRXQWULHVZHUHNHUDWRFRQXVDSSHDUV
WREHUDPSDQWZHHVWLPDWHWKDWLQHYHU\\RXQJDGXOWV
KDVWRSRJUDSKLFVLJQVRIWKHGLVHDVHWRSRJUDSK\VFUHHQLQJ
PD\EHWKHPRVWLPSRUWDQWSXEOLFKHDOWKGLDJQRVWLFPHGLFDO
WRRO :LWK WKH WLPHSURYHQ GLVHDVH FRXUVH DOWHUDWLRQ E\
&;/DQGRWKHUWHFKQLTXHLQWURGXFHGVLQFHOLNHWKH$WKHQV
3URWRFRO VFUHHQLQJ WHHQDJHUV IRU .&1 PD\ SURYH D OLIH
FKDQJLQJ PHGLFDO DVVHVVPHQW LQ UHJDUG WR WKHLU YLVXDO
5$)+,"2)'%)*'%*$&,'&"5-'62.7'%)*'9%:",$%&'2//2.,$)","-#8
!"#!$%&'"#
2XUVWXG\LQGLFDWHVWKDWYLVXDODFXLW\DQGFRUQHDOWKLFNQHVV
PD\ EH SRRU LQGLFDWRUV IRU NHUDWRFRQXV VHYHULW\ JUDGLQJ
DQGDFFXUDWHDVVHVVPHQWRISRVWRSHUDWLYHDVVHVVPHQW7KH
FRPSHOOLQJGLVHDVHVWDJLQJPDUNHUVDSSHDUWREHWZRDQWHULRU
VXUIDFHLUUHJXODULW\LQGLFHVGHULYHGE\6FKHLPSÀXJLPDJLQJ
QDPHO\WKHLQGH[RIVXUIDFHYDULDQFHDQGWKHLQGH[RIKHLJKW
!"#$%"&#'("&)*+(,%"&)*(-*.$%&#(/(",0*&"1*2/#&#'/*3(%"$&)*4'0$&0$05*6$7#$89$%:4$/$89$%*;<=>?;@>ABCD:=<>
!"!
!"#$%&
!"#$%#$&'$()'*"(+#",--'.'/-'$(,%(#-(
!"#$%#&'()*(+*,'-%#$*./%'&01*2#/3045&60*#)7*.)&56'(689%6+#/5*:665;%$#6'&0*')*<56#&(/()%-*#)7*=6(--$')>');*:)&56"5)&'()*?($$(@8%A
GHFHQWUDWLRQZKLFKDSSHDUWREHPRUHVHQVLWLYHDQGVSHFL¿F *RUGRQ6KDDJ$ 0LOORGRW 0 6KQHRU ( 7KH HSLGHPLRORJ\
DQGHWLRORJ\RINHUDWRFRQXV,QW-.HUDWRFR(FWDWLF&RUQHDO'LV
WRROV WKDQ YLVXDO DFXLW\ RU SDFK\PHWU\ LQ HDUO\ GLDJQRVLV
DQGSRVVLEOHSURJUHVVLRQLQNHUDWRFRQXVDQGFRUQHDOHFWDVLD
.DQHOORSRXORV$-$VLPHOOLV * &RUUHODWLRQ EHWZHHQ FHQWUDO
7KHVHLQGLFHVPD\EHFRPHDQRYHOEHQFKPDUNIRUIXWXUH
4,-'.!7# 03(4)'.11+# !'0.-(,-# 43!5/.-# &.803# !'&# 4,-'.!7#
VWXGLHVDQGPD\DLGLQWKHGHYHORSPHQWRIQHZNHUDWRFRQXV
NHUDWRPHWU\DVPHDVXUHGE\RFXO\]HULLDQGZDYHOLJKW2%
LQ SUHRSHUDWLYH FDWDUDFW VXUJHU\ SDWLHQWV - 5HIUDFW 6XUJ
GLDJQRVWLFDQGIROORZXSFULWHUL!"#
!"#$%&'(!)!*XVE\PHDQVRIDQWHULRUDQGSRVWHULRUWRSRJUDSKLF
DQDO\VLV&RUQHD
.DQHOORSRXORV$- &RPSDULVRQ RI VHTXHQWLDO YV VDPHGD\
VLPXOWDQHRXVFROODJHQFURVVOLQNLQJDQGWRSRJUDSK\JXLGHG35.
IRUWUHDWPHQWRINHUDWRFRQXV-5HIUDFW6XUJ6
!"#"!"$%"&
# $"# %!&'()# *+# %DUU -7 (GULQJWRQ 7% (YHUHWW ') -DPHVRQ 0
0F0DKRQ776KLQ-$6WHUOLQJ-/:DJQHU+*RUGRQ02
%DVHOLQH ¿QGLQJV LQ WKH FROODERUDWLYH ORQJLWXGLQDO HYDOXDWLRQ
RI NHUDWRFRQXV &/(. 6WXG\ ,QYHVW 2SKWKDOPRO 9LV 6FL
7DQ%%DNHU.&KHQ<//HZLV-:6KL/6ZDUW]7:DQJ0#
+RZ NHUDWRFRQXV LQÀXHQFHV RSWLFDO SHUIRUPDQFH RI WKH H\H#
-9LV
6DDG$*DWLQHO'(YDOXDWLRQRIWRWDODQGFRUQHDOZDYHIURQWKLJK
,-&.-#!/.--!0(,'1#2,-#03.#&.0.40(,'#,2#2,-5.#2-610.#).-!0,4,'61"#
,QYHVW2SKWKDOPRO9LV6FL
.DWVRXORV&.DUDJHRUJLDGLV/0RXVDIHLURSRXORV79DVLOHLRX
1 $VLPHOOLV * &XVWRPL]HG K\GURJHO FRQWDFW OHQVHV IRU
NHUDWRFRQXV LQFRUSRUDWLQJ FRUUHFWLRQ IRU YHUWLFDO FRPD
DEHUUDWLRQ2SKWKDOPLF3K\VLRO2SW
.UXHJHU 55 .DQHOORSRXORV$- 6WDELOLW\ RI VLPXOWDQHRXV
WRSRJUDSK\JXLGHGSKRWRUHIUDFWLYHNHUDWHFWRP\DQGULERÀDYLQ
89$ FURVVOLQNLQJ IRU SURJUHVVLYH NHUDWRFRQXV FDVH UHSRUWV#
-5HIUDFW6XUJ
.DQHOORSRXORV$-$VLPHOOLV * ,QWURGXFWLRQ RI TXDQWLWDWLYH
DQGTXDOLWDWLYHFRUQHDRSWLFDOFRKHUHQFHWRPRJUDSK\¿QGLQJV
LQGXFHGE\FROODJHQFURVVOLQNLQJIRUNHUDWRFRQXVDQRYHOHIIHFW
PHDVXUHPHQWEHQFKPDUN&OLQ2SKWKDOPRO
.DQHOORSRXORV $- /RQJWHUP UHVXOWV RI D SURVSHFWLYH
UDQGRPL]HG ELODWHUDO H\H FRPSDULVRQ WULDO RI KLJKHU ÀXHQFH
VKRUWHUGXUDWLRQXOWUDYLROHW$UDGLDWLRQDQGULERÀDYLQFROODJHQ
FURVV OLQNLQJ IRU SURJUHVVLYH NHUDWRFRQXV &OLQ 2SKWKDOPRO
.DQHOORSRXORV$-$VLPHOOLV*5HYLVLWLQJNHUDWRFRQXVGLDJQRVLV
DQGSURJUHVVLRQFODVVL¿FDWLRQEDVHG RQHYDOXDWLRQRIFRUQHDO
DV\PPHWU\ LQGLFHV GHULYHG IURP 6FKHLPSIOXJ LPDJLQJ LQ
NHUDWRFRQLFDQGVXVSHFWFDVHV&OLQ2SKWKDOPRO
/RSHV %7 5DPRV ,& )DULD&RUUHLD ) /X]$ GH )UHLWDV
9DOERQ%%HOLQ0:$PEUyVLR5-U&RUUHODWLRQRIWRSRPHWULF
DQG WRPRJUDSKLF LQGLFHV ZLWK YLVXDO DFXLW\ LQ SDWLHQWV ZLWK
NHUDWRFRQXV,QW-RI.HUDWDQG(FWDWLF'LV
&KDW]LV1+DIH]L)3URJUHVVLRQRINHUDWRFRQXVDQGHI¿FDF\
RIFRUQHDOFROODJHQFURVVOLQNLQJLQFKLOGUHQDQGDGROHVFHQWV#
-5HIUDFW6XUJ
/HJDUH0(,RYLHQR$<HXQJ61.LP3/LFKWLQJHU$+ROODQGV
66ORPRYLF$55RRWPDQ'6&RUQHDOFROODJHQFURVVOLQNLQJ
XVLQJULERÀDYLQDQGXOWUDYLROHW$IRUWKHWUHDWPHQWRIPLOGWR
PRGHUDWH NHUDWRFRQXV \HDU IROORZXS &DQ - 2SKWKDOPRO
.DQHOORSRXORV$-$VLPHOOLV*&RPSDULVRQRI3ODFLGRGLVFDQG
6FKHLPSÀXJ LPDJHGHULYHG WRSRJUDSK\JXLGHG H[FLPHU ODVHU
VXUIDFHQRUPDOL]DWLRQFRPELQHGZLWKKLJKHUÀXHQFH&;/WKH
$WKHQV3URWRFROLQSURJUHVVLYHNHUDWRFRQXV&OLQ2SKWKDOPRO
.DQHOORSRXORV$-$VLPHOOLV*.HUDWRFRQXVPDQDJHPHQWORQJ
WHUP VWDELOLW\ RI WRSRJUDSK\JXLGHG QRUPDOL]DWLRQ FRPELQHG
ZLWK KLJK ÀXHQFH &;/ VWDELOL]DWLRQ 7KH$WKHQV 3URWRFRO#
-5HIUDFW6XUJLQSUHVV
!"#
.DQHOORSRXORV$-$VLPHOOLV * /RQJWHUP EODGHOHVV /$6,.
RXWFRPHVZLWKWKH)6IHPWRVHFRQGDQG(;H[FLPHUODVHU
ZRUNVWDWLRQWKHUHIUDFWLYHVXLWH&OLQ2SKWKDOPRO
5DQGOHPDQ -% 7UDWWOHU :% 6WXOWLQJ 5' 9DOLGDWLRQ RI
WKH HFWDVLD ULVN VFRUH V\VWHP IRU SUHRSHUDWLYH ODVHU LQ VLWX
NHUDWRPLOHXVLVVFUHHQLQJ$P-2SKWKDOPRO
$PEUyVLR5-U&DLDGR$/*XHUUD)3/RX]DGD55R\$6/X]
$'XSSV:-%HOLQ0:1RYHOSDFK\PHWULFSDUDPHWHUVEDVHG
RQFRUQHDOWRPRJUDSK\IRUGLDJQRVLQJNHUDWRFRQXV-5HIUDFW
6XUJ
/L ; <DQJ + 5DELQRZLW] <6 .HUDWRFRQXV FODVVL¿FDWLRQ
VFKHPHEDVHGRQYLGHRNHUDWRJUDSK\DQGFOLQLFDOVLJQV-&DWDUDFW
5HIUDFW6XUJ
*UHHQVWHLQ 6$ )U\ ./ +HUVK 36 &RUQHDO WRSRJUDSK\
LQGLFHV DIWHU FRUQHDO FROODJHQ FURVVOLQNLQJ IRU NHUDWRFRQXV
DQGFRUQHDOHFWDVLDRQH\HDUUHVXOWV-&DWDUDFW5HIUDFW6XUJ
6RQPH]%'RDQ03+DPLOWRQ'5,GHQWL¿FDWLRQRIVFDQQLQJ
VOLWEHDP WRSRJUDSKLF SDUDPHWHUV LPSRUWDQW LQ GLVWLQJXLVKLQJ
QRUPDO IURP NHUDWRFRQLF FRUQHDO PRUSKRORJLF IHDWXUHV$P#
-2SKWKDOPRO
5DELQRZLW]<69LGHRNHUDWRJUDSKLFLQGLFHVWRDLGLQVFUHHQLQJ
IRUNHUDWRFRQXV-5HIUDFW6XUJ
$EDG-&5XELQIHOG56'HO9DOOH0%HOLQ0:.XUVWLQ-0
9HUWLFDO '$ QRYHO WRSRJUDSKLF SDWWHUQ LQ VRPH NHUDWRFRQXV
VXVSHFWV2SKWKDOPRORJ\
$PEURVLy56LPRQDWR5/X]$&RFD9HODUGH/*&RUQHDO
WKLFNQHVV VSDWLDO SURILOH DQG FRUQHDOYROXPH GLVWULEXWLRQ
WRPRJUDSKLFLQGLFHVWRGHWHFWNHUDWRFRQXV-&DWDUDFW5HIUDFW
6XUJ
6ZDUW]70DUWHQ/:DQJ00HDVXULQJWKHFRUQHDWKHODWHVW
GHYHORSPHQWV LQ FRUQHDO WRSRJUDSK\ &XUU 2SLQ 2SKWKDOPRO
+R-'7VDL&<7VDL5-.XR//7VDL,//LRX6:9DOLGLW\
RIWKHNHUDWRPHWULFLQGH[HYDOXDWLRQE\WKH3HQWDFDPURWDWLQJ
6FKHLPSIOXJ FDPHUD - &DWDUDFW 5HIUDFW 6XUJ #
)DULD&RUUHLD ) 5DPRV ,& /RSHV %7 6DORPmR 04 /X]
$ &RUUHD 52 %HOLQ 0:$PEUyVLR 5 -U 7RSRPHWULF DQG
WRPRJUDSKLFLQGLFHVIRUWKHGLDJQRVLVRINHUDWRFRQXV,QW-RI
.HUDWDQG(FWDWLF'LV
(PUH6'RJDQD\6<RORJOX6(YDOXDWLRQRIDQWHULRUVHJPHQW
SDUDPHWHUV LQ NHUDWRFRQLF H\HV PHDVXUHG ZLWK WKH 3HQWDFDP
V\VWHP-&DWDUDFW5HIUDFW6XUJ
6FKRQHYHOG 3 3HVXGRYV . &RVWHU '- 3UHGLFWLQJ YLVXDO
SHUIRUPDQFHIURPRSWLFDOTXDOLW\PHWULFVLQNHUDWRFRQXV&OLQ
([S2SWRP
$OLy -/ 3LxHUR '3 $OHVyQ $ 7HXV 0$ %DUUDTXHU 5,
0XUWD - 0DOGRQDGR 0- &DVWUR GH /XQD * *XWLpUUH] 5#
9LOOD & 8FHGD0RQWDQHV $ .HUDWRFRQXVLQWHJUDWHG
FKDUDFWHUL]DWLRQ FRQVLGHULQJ DQWHULRU FRUQHDO DEHUUDWLRQV
LQWHUQDO DVWLJPDWLVP DQG FRUQHDO ELRPHFKDQLFV - &DWDUDFW
5HIUDFW6XUJ
,VKLL 5 .DPL\D . ,JDUDVKL $ 6KLPL]X . 8WVXPL <
.XPDQRPLGR7&RUUHODWLRQRIFRUQHDOHOHYDWLRQZLWKVHYHULW\
!"#$%&%'(&!$%'#)*
!+,-.,-/0-&102+&3,+4550607500HGLFDO 'LUHFWRU /DVHUYLVLRQJU (\H ,QVWLWXWH$WKHQV *UHHFH
3URIHVVRU1HZ<RUN8QLYHUVLW\6FKRRORI0HGLFLQH1<86$
!"##$%&"'($')$*+((#$%%,7VRFKD6WU$WKHQV*UHHFH3KRQH
)D[HPDLODMN#EULOOLDQWYLVLRQFRP
8,-/5/9/&:07-.07
0HPEHU 'HSDUWPHQW RI 2SWRPHWU\ /DVHUYLVLRQJU (\H ,QVWLWXWH
$WKHQV*UHHFH
;40<=4&!-/>455/5HVHDUFK'LUHFWRU/DVHUYLVLRQJU(\H,QVWLWXWH$WKHQV*UHHFH
!"#$%"&#'("&)*+(,%"&)*(-*.$%&#(/(",0*&"1*2/#&#'/*3(%"$&)*4'0$&0$05*6$7#$89$%:4$/$89$%*;<=>?;@>ABCD:=<>
!"#

Handout CXL AJKdraft - American Society of Cataract and

Transcription

Similar documents

Accelerated CXL for the treatment of bullous keratopathy

Lotus Speculos

Part 1d

Corneal Collagen Cross-linking in a Prepubescent 10-Year

Improving LASIK`s and PRK`s Outcomes on Irregular Corneas

Post LASIK Ectasia - Ophthalmology and Visual Sciences

International Offshore Powerboat Race 2012 (Sarnia)

SoundSpeak

Actual Indications for Intracorneal Ring Segment