Piggyback contact lenses

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Piggyback
contact lenses
Course Code C-15914 O/D/CL
Claire McDonnell FAOI
Piggyback lens systems first emerged in the late 1960s. Westerhout,1 a
22/04/11 CET
pioneer of the system, first published a paper on their use in 1973. The
system consists of a rigid gas permeable (RGP) contact lens worn on top
of a soft contact lens. Piggyback lenses are normally used where an RGP is
Figure 1
The edges of a soft and an RGP lens highlighted
with fluorescein
indicated but cannot be tolerated by the patient or is inclined to decentre
eg, scarred corneas, high astigmatic ametropia and ectatic disorders such as
keratoconus and pellucid marginal degeneration. In the past, a combination
of a soft hydrogel lens and a RGP was used but this inevitably led to hypoxia
because of the low oxygen transmission through the combination of
lenses. Lately with the advent of high Dk silicone hydrogel (SiHy) lenses
Because many of the corneas being fitted
have a very steep central curvature,
SiHy lenses with shorter base curves
are preferred eg, Acuvue Advance
(Johnson & Johnson) (base curve 8.3).
Thought should also be given to the
and the discontinuation of the SoftPerm hybrid lens (after a product
modulus of the soft lens. Stiffer lenses
recall in 2010), piggyback lenses are enjoying something of a renaissance.
with a higher modulus can help mask
some of the cone in early keratoconus,
whereas lower modulus lenses are
Indications to fit
and as such piggyback lenses are a more
preferred in more advanced cases of
Piggyback lenses are mostly commonly
attractive option than RGPs alone. The
ectasia where a stiff lens may show edge
fitted when a previously successful
soft lens can be a coloured lens, which
fluting. Table 1 summarises the moduli
RGP lens fit becomes uncomfortable
may be particularly useful for eyes with
and base curves of popular SiHy lenses.
and patients find their wearing time
damage to the iris and for keratoconic
severely
advantages
patients who may experience less RGP
RGP lens selection
of the piggyback system are that it
movement if a coloured lens with
The RGP lens still needs to be a specialist
is more comfortable and causes less
a dot matrix opaque design is used.
lens (eg, Rose-K) or in some cases it may
corneal staining compared with RGPs
The disadvantages of the piggyback
be possible to use the patient’s existing
alone, particularly for eyes that may be
system are that it is more expensive
RGP lens. The drawback of using the
sensitive following surgery or trauma. In
than just using RGP lenses, given that
patient’s existing lens is that there can
a small study reported in Contact Lens
the patient has to pay for four lenses
be binding of the RGP on the new flatter
Spectrum, 18 out of 20 RGP wearers
instead of two, and that the care regime
surface created by the introduction
showed reduced staining after being
can be more onerous since both sets
of a soft lens. Regardless of the RGP
re-fitted with a piggyback lens system.
of lenses must be cleaned, perhaps
used, the material must have a high
with
Dk. Unfortunately, as Dk increases so
reduced.
The
2
The soft lens can be (and usually is)
3
different
systems
for
each.
does the material’s tendancy to flex and
a disposable lens, which results in
fewer problems of lens deposition.
Soft lens selection
ultimately warp; high Dk lenses also tend
Recently, researchers have found that
The soft lenses of choice that are used
to have shorter life spans than lower Dk
to delay the progression of keratoconus,
in piggyback systems are SiHy, owing
materials. Fluorosilicone acrylate (FSA)
trauma to the cornea must be minimised
to their high oxygen transmission.
materials are a good choice as they
provide good wettability
to older silicone acrylate
Fitting and
assessment
materials they attract less
The patient should
protein but more lipids.
be fitted with a low
and a high Dk. Compared
Table 2 summarises the Dk
powered
measurements for some
FSA
lenses.
lens
the
first
SiHy
and
the
49
fit assessed in the
Lens care
Ideally
(+0.50DS
-0.50DS)
normal
patient
needs a solution that is
have
and RGP lenses. Hydrogen
and
used with both lenses
leave the patient with a
movement
between
peroxide systems can be
step with peroxide can
A
soft
contact lens should
compatible with both soft
but carrying out a “rub”
way.
well-fitting
0.4mm
of
0.2mm
post-
blink in the primary
Figure 2
A RGP lens decentering infero-temporally on a soft lens on up-gaze
position of gaze. It
has been shown that
in a piggyback system, the contribution
slightly discoloured finger tip. Quattro
is a polyhexamethylene biguanide
used for the two different pairs of lenses
of power from the soft contact lens is
(PHMB)
multipurpose
but SiHy lenses have a documented
negligible5 (it has been suggested that
solution from Abatron which is safe
tendency to take up preservative and
the soft lens contributes only about 20%
to use with both lens types. It also
later release it when the lens is in situ,4
of its power in air). Once a satisfactory
contains surfactants, which makes it
and this can, in some cases, cause corneal
soft fit has been achieved, keratometry
useful for the removal of lipid deposits
insult. Therefore it is probably safer
(K) or topography readings can now be
– an important consideration for SiHy
to avoid any contact between the SiHy
taken with the soft lens in situ. The base
lenses. Two separate systems can be
lens and an unsuitable RGP solution.
curve of the initial trial RGP lens should
preserved
Lens
Base Curves (mm)
Total Diameter
(mm)
Modulus (MPa)
Acuvue Advance
(Johnson & Johnson)
8.3
8.7
14.0
0.43
Clariti 1-day
(Sauflon)
8.6
14.1
0.5
Acuvue Trueye
(Johnson & Johnson)
8.5
9.0
14.2
0.66
Acuvue Oasys
(Johnson & Johnson)
8.4
8.8
14.0
0.72
Biofinity
(CooperVision)
8.7
14.0
0.8
AirOptix
(Ciba Vision)
8.6
14.2
1.0
Table 1
Characteristics of popular silicone hyrdogel contact lenses
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common
or
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be based on these K-readings
6/12 and combined
with a total diameter of 9.0mm
binocularly with the
to 9.5mm. The fit of the RGP
uncorrected left eye
lens on top of the soft lens is
was
also assessed in the normal
three-week follow-up
way. Special high molecular
aftercare appointment,
the patient reported
into the soft lens, but it does
not fluoresce as brightly as
regular fluorescein and is more
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Figure 3
A decentred RGP lens with central bubble
lenses
more
SoftPerm
Reverse piggyback
did not want to be fitted with an RGP lens
(Figure 1). Fluorescein will also allow
as she had tried them before but never
visualisation of any fluting of the soft
found them comfortable. She agreed to try
lens edges. If there is fluting, a soft lens
a piggyback lens system for her right eye.
with a lower modulus should be tried.
Patient
If the fit of the RGP lens is not adequate,
6/24 in the right eye and 6/12 in
the fitting characteristics can be changed
the
by altering the power of the underlying
corrected distance VA were as follows:
soft lens. A steep RGP fit can be flattened
RE:
-2.50/-6.00x15,
VA
by increasing positive power of the soft
LE:
+0.75/-3.50x145,
VA
GMJ’s
left
unaided
eye.
Her
vision
refraction
=
=
was
and
6/19
6/9.5-1
lens and a flat fit can be improved by
There was distortion of the mires on
increasing negative power in the soft lens.
keratometry but no Fleischer’s ring or
A minus-powered soft lens with a thin
Vogt’s striae were visible on slit lamp
centre and a thicker edge can effectively
examination. The soft lens fitted for the
“flatten”
help
right eye was Acuvue Oasys (Johnson
improve the fit of an RGP with excessive
& Johnson), which has a base curve of
edge lift. A plus-powered soft lens with
8.4mm and a total diameter of 14.0mm;
a thicker centre may help improve
a power of -0.50DS was selected. The
centration of an RGP and can help to
fit of the lens was acceptable and the
improve an initially steep-fitting RGP.
K-readings with the soft lens in place
may
the
wear them all day.
use regular fluorescein with these lenses
and
found
lens, and she could
and therefore it is normally acceptable to
cornea
she
previous
to rinse the dye from most SiHy lenses
the
that
comfortable than her
expensive. Since SiHy lenses
materials do, it is easy enough
her
staining or hypoxia,
used to prevent the dye soaking
the same way that hydrogel
At
there were no signs of
weight fluorescein should be
do not pick up fluorescein in
6/9.5.
were RE: 7.46@25, 6.73@115. A trial
It is also possible to wear reverse
piggyback lenses where a soft lens is
worn over a small diameter RGP lens, in
order to prevent the loss or decentration
of an unstable RGP on a badly damaged
cornea. This system is mostly used on
an occasional basis by patients during
certain sporting activities where there
is an increased risk of RGP loss. Ideally
the soft lens needs to be a large diameter,
thin lens that drapes well, and so a
spun cast lens such as the Bausch &
Lomb Soflens daily disposable (total
diameter
14.2mm)
can
As far as the author is aware, the only
hybrid lenses still available in the UK
Material
Dk
Rose-K lens of base curve 7.40mm was
Boston EO
58
Patient GMJ was diagnosed with bilateral
placed on top of the soft lens and the
Paragon HDS
58
keratoconus in 2002. She had subsequently
fit assessed with high molecular weight
been fitted with a SoftPerm hybrid lens in
fluorescein.
Fluoroperm 60
60
her right eye only (she did not feel she
showed central touch and so a steeper
needed a distance correction for her left
lens was trialled. Her final lens fit was:
Boston XO
100
eye). She came into the practice because
RE: Acuvue Oasys 8.40/14.0 -0.50DS
Paragon HDS 100
100
she had lost her SoftPerm lens and wanted
with Rose-K 7.11/9.00 -5.00 (Boston XO).
a replacement. It was explained to her that
With these lenses in place the patient’s
SoftPerm were no longer available. She
monocular VA with her right eye was
fluorescein
pattern
well.
Hybrid lenses
Case study
The
work
Table 2
Dk of common fluorosilicone acrylate RGP lenses
Lens Name
Indications
ClearKone
Advanced keratoconus
Pellucid marginal degeneration
Keratoglobus
SynergEyes PS
(Post-surgery)
Pentrating keratoplasty
Intacs
Corneal trauma
SynergEyes MF
Simulataneous multifocal lens for presbyopia
Duette
Astigmatic and spherical ametropia, with normal
corneas
Soft Skirt
RGP Centre
Hemiberfilcon A
Dk 9.3
Paflufocon D
Dk 145
51
MaxVU
Dk 130
Table 3
Hybrid lenses availability from SynergEyes
and Ireland are made by SynergEyes.
piggyback lens system. This differs
Conclusion
This company has a website available
from the standard system in that the
Given that the problems of hypoxia have
for practitioners wishing to transition
soft lens has a recess or cut-out section
now been overcome with the advent
existing SoftPerm wearers into their
on the front lens surface that allows
of high Dk SiHy lenses, piggyback
new hybrid lenses. Until recently, the
for placement of the RGP within the
lens systems should definitely be
skirts of these new hybrid lenses were
recess, thus overcoming some of the
considered
all made from a hydrogel material with a
problems of decentration. The FlexLens
irregular corneas and RGP intolerance.
Dk of only 9.3. In January 2011 however,
manufactured by X-Cel laboratories
The fitting of piggyback lenses requires
the FDA approved a new hybrid lens
is such a lens. It is custom-made, but
little or no additional expertise other
with a SiHy skirt with a Dk of 84. This
to-date has only been available in
than being aware of other forms of soft
lens is not currently designed for ectatic
hydrogel materials (Table 4). Another
and RGP lenses. For some patients
corneas. The hybrid lenses available
newer lens called the RPLS (Recessed
with ectatic corneas a piggyback lens
from SynergEyes are listed in Table 3.
Pillow
currently
system may prevent and/or delay
in development and evaluation by
the need for a corneal graft and that
Fusion Technologies and EyeVis Eye
can surely only be a good thing.
Alternative approaches
lens
System)
is
for
all
patients
with
In spite of the many advantages of
and Vision Technologies. It is not yet
piggyback
are
commercially available but options to
still some fits that fail, usually due to
About the author
produce the lens in SiHy materials are
Claire McDonnell qualified as an
being investigated. The diameter, base
optometrist in 1997. She has since
curve, peripheral curve, and centre
worked in private practice, refractive
thickness can all be customised with
surgery and education in Ireland,
these lenses. All parameters are utilised
the UK and New Zealand. She is
to optimise physical fit and movement
currently a lecturer in the Department
characteristics. The recess also has a
of Optometry in the Dublin Institute
customisable diameter to account for
of
the various RGP lens diameters that
contact
are placed within the recess. Typically
and
lens
systems,
there
difficulties centring the RGP lens on
very irregular corneas (Figures 2 and 3).
This can be overcome using a custom
Material
Dk
Hefilcon A
13.2
Hioxifilcon B
15
Methafilcon A
18
Acofilcon A
25.5
Table 4
Material and Dk values of the FlexLens for
piggyback systems
6
Technology.
lenses,
advanced
She
lectures
refractive
clinical
in
surgery
techniques.
the recess diameter is about 0.3mm
larger than the overall RGP diameter
Reference
resulting in a snug fit of the RGP such
See http://www.optometry.co.uk
that the movement is totally controlled
clinical/index.
by the RPLS “pillow” lens (i.e. the
article
RGP does not move within the recess).7
download
title
Click
on
and
the
then
“references”.
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Flex20 (SiHy)
Dk 84
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Course code: C-16011 O/D
Course code: C-15914 O/D/CL
1.Conjunctival naevi have all the following features EXCEPT:
a) A cystic component
b) Appearance in the first decade of life
c) A low risk of malignant transformation
d) They metastasise to the regional lymph nodes
1. Which of the following contact lens care systems is suitable for
use with both RGPs and soft contact lenses?
a) Biotrue
b) Quattro
c) Complete
d) Focus Aqua
2. Which of the following statements about racial melanosis is FALSE?
a) It is a bilateral symmetrical conjunctival pigment
b) It is acquired in early life
c) The pigment is typically confined to the bulbar conjunctiva
d) Typical cases require referral to ophthalmology
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3. Why should congenital oculodermal melanocytosis be referred to
ophthalmology?
a) Because there is risk of uveal tract, orbital and intracranial melanoma
b) Because there is risk of glaucoma
c) Because there is risk of conjunctival squamous cell carcinoma
d) Because there is risk of colour vision defects
4. When is referral of Primary Acquired Melanosis to ophthalmology
NOT indicated?
a) A new nodule develops in an otherwise flat lesion
b) Dilated vessels are present within the pigment
c) The pigment disappears
d) There is tarsal conjunctival pigmentation
5. Which of the following statements about conjunctival melanoma is
FALSE?
a) It may be associated with FAM-M syndrome
b) It metastasises to the regional lymph nodes
c) It is associated with a 70% -75% 10-year survival
d) Incisional biopsy must be performed
6. Sentinel lymph node biopsy should be considered in all of the
following EXCEPT:
a) Conjunctival melanoma in a non-limbal location
b) Conjunctival melanoma with enlarged regional lymph nodes
c) Conjunctival melanoma >2mm thick
d) Conjunctival melanoma >2mm thick at the limbus
2. Which of the following statements about piggyback systems
is TRUE?
a) A higher modulus soft lens is required if the RGP lens fit on top is steep
b) Low modulus soft lenses are more likely to show edge fluting compared
with higher modulus lenses
c) A low modulus lens is better for corneas with more advanced ectasia
d) The lowest modulus silicone hydrogel lens is a daily disposable
3. Which of the following hybrid lenses is still available?
a) SoftPerm
b) FlexLens
c) RPLS lens
d) SynergEyes
4. Which of the following statements about piggyback systems is
TRUE?
a) A higher oxygen transmission in an RGP increases its likelihood to flex
b) Silicone acrylate RGP materials are best for piggyback systems
c) Fluorosilicone acrylate material attracts more protein than silicone acrylate
d) A non-specialist RGP lens can be used for a keratoconic cornea system
5. What is a custom piggyback lens system?
a) When a soft lens is worn over an RGP lens
b) When a patient is fitted with a soft lens and their own existing RGP lens
c) When a topographer is used for the fitting process
d) When the soft lens contains a recess in its front surface for the RGP lens
6. Which of the following statements about reverse piggyback
systems is TRUE?
a) It needs a soft lens with a large total diameter
b) It needs an RGP lens with a large total diameter
c) It needs a relatively high modulus soft lens
d) The RGP lens diameter should be 1-2mm less than the soft lens diameter