Incidence

Silicon
oil is a frequently utilized adjunct to surgical repair of complex retinal
detachment. Glaucoma can complicate the post-operative course of such procedures
with incidence that varies between 2.2% and 56%1,2. Mechanism of intraocular pressure (IOP) elevation
can be from acute angle closure with or without pupillary block; open-angle
glaucoma with silicone oil in the anterior chamber; rubeosis irides leading to
secondary angle closure; or primary open-angle glaucoma.

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Risk factors Several risk factors for development of IOP elevation have been
studied previously but remained unclear. These include preexisting glaucoma,
diabetes, and aphakia3, silicone oil in the anterior chamber; early
postop pressure spike; trauma; and postop neovascularization of the iris. Also, an
association has been found with the quantity of emulsified oil in the AC and
the use of heavy tamponading agents4

Pathophysiology

Several
mechanisms of IOP elevation have been proposed and are generally classified into
early postoperative IOP elevation and late-onset glaucoma. Early IOP elevation may be from preexisting glaucoma, pupillary
block, inflammation, and/or mechanical impediment to filtration caused by displaced
silicone oil into the AC. Late-onset IOP elevation can be caused by infiltration of the
trabecular meshwork by silicone bubbles, synechially closed angle, iris neovascularization,
and/or primary open angle glaucoma4.

Management
Treatment strategy of silicone oil related glaucoma should be based on the mechanism
of IOP elevation. Topical antiglaucoma medication coupled with cycloplegics and
steroids may effectively lower IOP in 30-78% of patients2,5. Eyes with silicone oil are at risk of
pupillary block glau. however, spontaneous closure of PI may occur in 11-32% of
cases and need to be reopened2,4,6.

Cyclophotoablation
may be an alternative in eyes at high risk of re-detachment after silicone oil
removal, or in eyes with poor visual potential. However, no data on success
rate were reported in literature.

 

Decision
for therapeutic early silicon oil removal is usually made difficult by the significant
risk of re-detachment (11-33%)2. Reported rates of IOP normalization after
silicone oil removal varies widely. In one study, SOR resulted in control of
IOP in 93.4% of patients, whereas another study reported persistence in all
eyes even after silicone oil removal7,8. Some researchers attribute the persistent IOP
rise after silicone oil removal to inflammation of the trabecular meshwork, and
its obstruction by silicone oil droplets4. Other studies compared results of SOR with
incisional glaucoma surgery versus either one done alone yielding variable
results2,9,10.

Incisional
glaucoma surgery and shunt implants may be considered in patients with unresponsive
glaucoma, especially in eyes where the angle is synechially closed. However, trabeculectomy
can be technically difficult due to subconjunctival fibrosis from prior retinal
surgery, and carry high risk of complications and failure. As an alternative, inferiorly
placed glaucoma valve implant can be used with success rate of  86% at 6 months and 76% at one year after
implantation5

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