Pars Plana Vitrectomy

Clinical
Pars Plana Vitrectomy
Dr. Preethika Gandhi, MS Resident, Aravind Eye Hospital, Madurai
Since the introduction of pars plana vitrectomy
in the early 1970s by Machemer, advances
in the field of vitreoretinal surgery have been
dramatic. Machemer initially performed pars
plana vitrectomy with the use of a 17gauge
(1.5mm diameter) multifunctional instrument
capable of cutting and aspirating the vitreous.
This instrument utilized a fibre optic sleeve
and required a 2.3mm scleral incision. In 1974,
O’Malley designed a smaller vitreous cutter
with a diameter of 0.9mm (20-gauge)1. This less
invasive 3 port 20-gauge cannula entry system is
still used today. In 1990, de Juan and colleagues
designed a variety of 25 gauge (0.5 mm diameter)
vitreoretinal instruments for more delicate and
precise surgical maneuvers2. Recently, Fuji et al
designed a 25-gauge microcannular system and
an array of 25-gauge instruments referred to as
transconjunctival sutureless vitrectomy system
(TSV)3. This was followed by the introduction of
a 23 gauge system by Eckardt in 20054.
Cataract development and progression are
frequent complications of phakic pars plana
vitrectomy5-18. Apart from the surgical technique
of PPV, there are other factors that worsen the
progression of the cataract formation like age,
pre-operative nuclear sclerosis, intraoperative lens
touch, diabetic retinopathy, silicone oil injection
and length of follow up.
As the surgical techniques and outcomes are
improving and indications of pars plana vitrectomy
are expanding, the rate of cataract extraction after
PPV are on the rise. Hence it is very important to
understand the principles of pars plana vitrectomy
and the anatomical alterations it causes in the
eye so as to be aware of the complications and
challenges we might encounter intraoperatively
and post operatively.
Vitreous
Vitreous is a transparent, colourless, gel
like structure which occupies the posterior
compartment of the eye. It comprises about 80%
of the total volume of the globe (two third of total
volume of eye), about 4ml. The surfaces of the
intraocular structures that interface with vitreous
are mainly basement membrane in nature eg. Pars
plana of ciliary body, internal limiting membrane
of retina and vitreous is attached to them with
varying strength of adhesion.
Vitreous is attached to its surrounding
structures by condensation of collagen fibrils.
From strongest to weakest, these are:
• Vitreous base-strongest
• Posterior lens capsule with hyaloideocapsular
ligament of Weiger
• Margins of the optic disc
• At the macula
• Along the retinal vessels – Most variable and
weakest
The vitreous base is the place of strongest
adhesion of vitreous. Vitreous base forms a band
of 4 to 6 mm width (1 to 2mm anterior to the ora
serrata and 1 to 3mm posterior to it) which lies in
the posterior aspect of the pars plana and adjacent
to the anterior aspect of the ora serrate. There is
strong adhesion between vitreous fibres of the
vitreous base region and basement membrane of
the nonpigmented epithelium of the ciliary body
and internal limiting membrane of the periphery
of the retina.
Pars plana is a circular tract that extends from
the ora serrata, forward to the posterior part of the
ciliary processes – also called ciliary ring, orbiculus
ciliaris. It is through this approach that the vitreous
cavity is entered.
Vol. XV, No.2, April - June 2015
Indications of Vitrectomy (posterior
segment indications)
1. Non resolving vitreous opacities
- Vitreous haemorrhages
- Vitreous membranes
2. Proliferative retinopathies
a. Proliferative Diabetic retinopathy:
o Vitreous haemorrhage
o Tractional retinal detachment involving
the macula
o Combined tractional and rhegmatogenous
retinal detachment
o Early rubeosis with vitreous haemorrhage
b. Eale's Disease
c. Branch Retinal vein occlusion
d. Proliferative sickle cell retinopathy
e. Retinopathy of prematurity
3. Selected cause of retinal detachments
a. Proliferative vitreo retinopathy grade C2
or more
b. Giant retinal tears and dialysis
c. Posterior breaks and macular holes
d. Associated with vitreous haemorrhage
e. Combined RRD and TRD
f. Colobomatous detachments
g. Inadequate pupillary space
4. Trauma: Blunt or penetrating trauma,
associated either with retained intraocular
foreign body or vitreous incarceration in the
anterior segment wound.
5. Vitreous biopsy
6. Vitreomacular traction
7. Epiretinal membranes
8. Impending and full thickness macular hole
Technique of vitrectomy surgery
- Can be performed under local or general
anaesthesia
- For local anaesthesia, a mixture of 2% xylocaine
with 0.5% bupivacaine with hyaluronidase is
commonly employed through the peribulbar
route or retrobulbar route. General anaesthesia
15
-
-
-
-
-
-
-
-
-
is preferred in younger individuals and in
complicated cases.
Good pupillary dilatation is essential
After standard preparation and draping of the
patient, the bridle sutures are taken for aiding
the stabilization of the globe.
Making 2 conjunctival incisions, 3 linear,
limbus parallel 1.4 mm long sclerotomies are
made using symmetric sharp blades also known
as microvitreoretinal blades which allow the
introduction of the 20G/25G instruments into
the eye.
The sclerotomies are placed in the pars plana
region, 4mm from the limbus in phakics,
3.5mm from limbus in pseudophakics and
children and 3mm from limbus in aphakics.
These sclerotomies are usually placed in the
mid or anterior part of the pars plana to avoid
the vitreous base which is a 3mm wide zone
of firm vitreoretinal attachment straddling the
ora serrata.
The infusion cannula is usually secured in
the inferotemporal quadrant just beneath the
lateral rectus.
The upper 2 sclerotomies are placed 140 degrees
apart to facilitate bimanual manipulation.
The exent of intraocular manipulation
performed, depends on the indication for
which the vitrectomy is being performed.
In order to prevent damage to the crystalline
lens during vitrectomy, a few tiny air bubbles
are introduced through the pars plana which
help in determining the posterior lens capsule.
Vitreous substitutes
Vitreous substitutes are those which are used to
replace the volume of vitreous after the vitrectomy.
Purpose of vitreous substitutes:
• To expand / replace vitreous volume
• To exchange opaque vitreous with optically
clear material
• To tamponade the vitreous
• To mechanically separate the epiretinal tissue
from retina
16
Materials used
Of the many gases that are available, commonly
used intraocular gases are air, SF6, C3F8.
Gases AVG duration Largest
of action size by
Air 3 days
Immediate
Average
expansion
No expansion
SF6
12 days 36 hrs
Doubles
C3F8 38 days
3 days
Quadruples
Complications of intraocular gases
• During injection of gas
• Contact of the bubble to posterior lens –
immediate postoperative rise in IOP.
• Lens opacities
• Bullous keratopathy
• New break formation
Silicone Oil
Silicone oils are linear synthetic polymers of
dimethylsiloxane, having a common chain of
repetitive siloxane units. Molecular weight is
determined by the length of the chain. It is a
clear transparent, inert, non-carcinogenic, heat
resistant liquid with a refractive index of 1.4035
and a specific gravity of 0.97.
Complications of silicone oil insertion
• Emulsification – most common complication
leading to emulsified oil in anterior chamber
causing inverse hypopyon (hyperleon).
• Cataract – incidence maximum between 6 to
8 months after surgery, 100% in 2 years.
• Glaucoma
• Band shaped keratopathy
• Redetachment after removal of the oil.
Refractive status of eye following silicone
oil insertion:19
• In phakics and pseudophakics due to concave
anterior surface of the bubble, it causes
hypermetropia of about +5.00 diopters.
AECS Illumination
• In aphakics, due to convex anterior surface it
causes myopia.
An article on “Refractive Outcomes of
phacoemulsification and intraocular lens
implantation after pars plana vitrectomy” revealed
a more hyperopic shift in those who underwent
phacoemulsification in vitrectomized eyes, than
in non vitrectomized eyes.
Perfluorocarbon liquids
Useful in certain cases of vitrectomy. They are
heavy fluids, hence displace subretinal fluid
anteriorly which can pass through the retinal
breaks and aid in flattening the retina. It has to be
completely removed at the end of the surgery in
order to prevent complications following residual
droplets.
Miscellaneous
1. Balanced Salt Solution
2. Sodium Hyaluronate
Complications of pars plana vitrectomy
• Postoperative nuclear sclerotic cataract
• Long term risk of open angle glaucoma
• Intraoperative or post-operative retinal break
• Intraoperative or post-operative retinal
detachment
• Intraoperative cataract
• Postoperative vitreous haemorrhage
• Postoperative massive fibrin accumulation
• Postoperative anterior segment
neovascularisation
Complications associated with silicone
oils
• Glaucoma
• Band Keratopathy
Complications associated with IOL surgery
in general
• Endophthalmitis
• Sympathetic Ophthalmia
• Recurrent corneal erosions
Vol. XV, No.2, April - June 2015
Likely risk factors for the development of cataract
• Older age6,13,18
• Preoperative nuclear sclerosis10
• Intraoperative lens touch
• Diabetic retinopathy12
• Silicone oil injections 20,21
• Length of follow up10-17
Previous vitrectomy presents a challenge for the
cataract surgeon because of the potential that
complications can occur.
17
These may include;
• Poor pupillary dilatation
• Posterior synechiae
• Zonular damage or weakness
• Posterior capsule tears
• Increased mobility of the lens iris diaphragm
• Altered intraocular fluid dynamics as a result
of absence of hyaloids
• Underlying comorbidities
• Sequelae of previous surgical trauma and
inflammation
Reference:
1. O. Malley C,Heintz RM Sr. Vitrectomy with an alternative instrument system. Ann Ophthalmol
1975;7(4) : 584 -585.
2. De Juan E Jr, Hickingbotham D. Refinements in micro instrumentation for vitreous surgery. Am J
Ophthalmol 1990; 109 (2) : 218-220.
3. Fujii GY, de Juan E Jr, Humayun MS, et al. A new 25-gauge instrument system for transconjunctival
sutureless vitrectomy surgery Ophthalmology 2002; 109:1807-1813.
4. Eckardt C. Transcojunctival sutureless 23-gauge vitrectomy. Retina 2004; 25:208-211.
5. Blankenship GW, Machemer R. Long term diabetic vitrectomy results. Report of 10 year followup.
Ophthalmology 1985; 92 : 503 – 6.
6. Margherio RR, Cox MS, Jr, Trese MT, et al. Removal of epimacular membranes. Ophthalmology 1985;
92: 1075-83.
7. Mc.Dermott ML, Puklin JE Abrams GW Elliot D.Phacoemulsification for cataract following pars plana
vitrectomy. Ophthalmologic surgery Lasers 1997; 28: 558 – 564.
8. Hutton WL. Pesicka GA. Fuller DG. Cataract extraction in the diabetic eye after vitrectomy. Am J
Ophthalmol 1987:104:1-4.
9. De Bustros S, Thompson JT, Michels RG, et al, Nuclear sclerosis after vitrectomy for idiopathic epiretinal
membranes. Am J Ophthalmol 1988 ; 105 : 160 – 4.
10.Poliner LS, Olk RJ, Grand MG, et al. Surgical management of premacular fibrosis. Arch Ophthalmol
1988; 106 : 761 – 4.
11.Grewing R, Mester U, Linsentrubungen nach pars plane vitrectomie bei diabeterischer. Fortschr
ophthalmol 1990; 87 : 440 -2.
12.Pesin SR, Olk RJ, Grand MG, et al. Vitrectomy for premacular fibroplasia. Prognostic factors, long term
follow up, and time course of visual improvement. Ophthalmology 1991; 98 : 1109-14.
13.Nakazawa M, Kimizuka Y, Watabe T et al. Visual outcome after vitrectomy for diabetic retinopathy. A
five year follow up. Acta Ophthalmol 1993; 71 : 219-23
14.Ogura Y, Kitagawa K, Ogino N.Prospective longitudinal studies on lens changes after vitrectomy –
quantitative assessment by fluorophotometry and refractometry. Nippon Ganka Gakkai Zasshi 1993; 97 :
627 – 31.
18
AECS Illumination
15.Licke K.Laqua H. The treatment of complicated Retinal Detachment. Berlin Springer – Verlag 1990.
16.Borislav D. Cataract after silicone oil implantation. Doc ophthalmol 1993; 83 : 79 – 82.
17.Fish MJ, Cairns DJ. Silicone oil insertion. A review of 127 consecutive cases. Aust N Z J Ophthalmol
1995; 23 : 25 -32.
18.Blankenship GW. Stability of pars plana vitrectomy results for diabetic retinopathy complications. A
comparison of 5 year and 6 month post vitrestomy findings. Arch Ophthalmol 1981; 99 : 1009 – 1012.
19.Meyers SK, Klein R, Chandra S, Myers FL. Unplanned extracapsular cataract extraction in post vitrectomy
eyes. Am J Ophthalmol 1978; 86 : 624 – 26.
20.J. Javitt JC, Teilsch JM, Canner JK, et al. National outcomes of cataract extraction. Increased risk of
retinal complications associated with ND:YAG capsulotomy. The cataract patient outcomes research team.
Ophthalmology 1992; 99 : 1487 – 97.
21.Teilsch JM, Legro MW, Cassard SD, et al. Risk factors for retinal detachment after cataract surgery. A
population based case – control study. Ophthalmology 1996; 103 : 1537 – 45.