Silicone oil tamponade forms an important aspect of vitreoretinal procedures, especially in cases of complicated retinal detachments.1 Intraocular silicone oil is associated with a number of complications (keratopathy, glaucoma, cataract, subretinal migration of silicone oil, reproliferation of epiretinal and subretinal fibrous membranes) if left in situ for an extended period of time.2,3 The indications, type of silicone oil used and the technique of injection has undergone major variations in the last four decades.4 The histopathological evaluation of silicone retinopathy in monkeys using electron microscopy dates back to 1975.5 We report a histopathological study of eight enucleated silicone oil-filled eyes done in our ocular pathology laboratory during a period of six years (from 2000 to 2005) to demonstrate the patterns of intraocular migration of silicone oil.
Materials and Methods
Fixation of eyeball specimen was done in 10% formaldehyde for 12 to 24 h. Before sectioning, the clinical summary was reviewed thoroughly for the history, surgical procedure, indication for enucleation, and the duration of silicone oil inside the eye.
The globe was opened horizontally, 2 to 4 mm on either side of the optic nerve. The globe was opened in such a way to include the pupil and optic nerve in the same section. The section of the globe was then examined and photographed from anterior to posterior starting from the cornea till the sclera and optic nerve and then the histopathological slide stained with hematoxylin and eosin was prepared [Figures 1 to 9]. The histopathological study was carried out under light microscopy.
Eight eyes of eight patients were included in the study after enucleation and histopathological analysis was carried out as a retrospective chart review. The clinical data and the histopathological reports were recorded and analyzed. The mean age of the patients was 27.5 years (range, 10 to 42 years). Seven of eight patients were males (87.5%). The primary indications for silicone oil injection was penetrating injury in five eyes, blunt injury in two eyes, and proliferative diabetic retinopathy in one eye. The mean duration of silicone oil tamponade was 81.14 months (range, 2 to 120 months). In all cases 1000 centi-stokes silicone oil was used. At the time of enucleation, four patients had low intraocular pressure and two patients had neovascular glaucoma. All patients had multiple intraocular surgeries (at least three) prior to enucleation. The eyes which underwent primary repair for ocular trauma for an open globe injury had the longest duration of silicone oil tamponade (74, 120, 120 months respectively). None of these eyes showed raised intraocular pressure or neovascular glaucoma, and the silicone oil vacuoles were seen only in the retinal tissue on histopathology. The longer duration of silicone oil tamponade did not influence the intraocular migration of oil vacuoles into various tissues. The most extensive distribution of silicone oil was observed in three eyes. The first eye had a history of penetrating injury, with the duration of silicone oil in the eye being 74 months, with recurrent retinal detachment postoperatively, and the silicone oil vacuoles were found in the conjunctiva, cornea, retro- corneal membrane, ciliary body, iris, retina and subretinal membranes. The second eye was also post traumatic, with the duration of silicone oil tamponade of 84 months, and the oil vacuoles were found in angle structures, iris, ciliary body, and the retina (most notably the inner retinal layers). In both these cases, there was extensive bare choroid. The third eye had proliferative diabetic retinopathy, with the duration of tamponade being only two months, and the silicone oil vacuoles being present in the conjunctiva, anterior chamber, iris, ciliary body, angle, retina and the optic nerve [Table 1]. The eyes which developed neovascular glaucoma (two of eight eyes) before enucleation (one with proliferative diabetic retinopathy, and other with penetrating trauma) showed the presence of silicone oil vacuoles in the optic nerve tissue. The histopathology of the enucleated eyes also showed the presence of chronic inflammatory cellular infiltration in all the ocular tissues, most notably in close proximity to the silicone oil vacuoles.
An earlier study by Knorr et al., had showed the presence of silicone oil vacuoles in the retina as early as four weeks after oil injection.6 They had also shown the presence of silicone oil vacuoles in the optic nerve along with the retina in the eyes with raised intraocular pressure. In the same study, the authors had concluded that there was no clinicohistopathological correlation between the presence of vacuoles in the retina or optic nerve and the duration and viscosity of intraocular silicone oil. Our results corroborate with the results previously described, and we also showed the presence of silicone oil in various tissues in all the eyes, earliest being two months after silicone oil injection. We found that there is no association of intraocular migration of silicone oil with the age, the etiology for intraocular tamponade, duration of silicone oil inside the eye, or postoperative course. The presence of oil vacuoles in the optic nerve is correlated with raised intraocular pressure and we are of the opinion that the eyes with raised intraocular pressure are more prone to optic nerve damage due to silicone oil and should be considered for an earlier oil removal surgery.
Wickham et al., have recently shown that the focal areas of intraretinal silicone oil were associated with disorganized retinal architecture, retinectomy sites or subretinal oil, and that the distribution of macrophages was closely related to the distribution of silicone oil.7 Chronic inflammatory cellular infiltration was observed in all the eyes examined by us, most notably in the vicinity of silicone oil vacuoles in the retinal tissue, where the silicone oil vacuoles were shown to be consistently present. The other ocular tissues also showed the chronic inflammatory cellular infiltration associated with silicone oil migration in that tissue.
Authors also found more extensive intraocular distribution of silicone oil either in case of proliferative diabetic retinopathy, or in eyes with large areas of bare choroid. The same observation was made by Basin et al.8 The authors hypothesize that the complicated and more extensive surgeries in these eyes, along with the exposure of a large area of choroid with silicone oil, increase chance of silicone oil to enter the choroidal vessels.
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