Is silicone oil optic neuropathy caused by high intraocular pressure alone? A semi-biological model

Silicone oil endotamponade is used for the repair of complicated retinal detachments. Cataract, glaucoma and corneal endothelial dysfunction are the most frequent complications of silicone oil tamponade. Clinical and histopathological studies have revealed that silicone oil can penetrate into the optic nerve and into the brain. The mechanism by which silicone oil moves from intraocular into the optic nerve is still under debate. To investigate the effect of intraocular pressure only, a post-mortem experimental histological study was performed to determine whether silicone oil penetration from the globe into the optic nerve after vitrectomy and silicone oil instillation is a purely pressure-related phenomenon. Although a post-mortem study excludes physiological processes, it serves as a model for the study of pure physical forces onto biological structures.

The study was carried out on 20 human eyes with their optic nerves attached. All specimens had been harvested from patients without known eye disease. The vitreous body was removed with a syringe and the globe was filled with silicone oil. A lipophil fluorescence marker (Bodipy) was added in 8 eyes. The mean intraocular pressure after silicone oil filling measured 40 mm Hg and the globes stayed under pressure for up to 16 weeks. The eyes and optic nerves were stained with H&E and examined with light, phase-contrast and fluorescence microscopy.

None of the 20 specimens examined showed silicone oil in the retrolaminar portion of the optic nerve.

Migration of silicone oil into the optic nerve was not demonstrated in this human post-mortem study. Therefore other factors, such as pre-existing glaucomatous damage to the disc region and/or active transport mechanisms must be involved in the development of silicone oil-associated optic neuropathy.