Long-term exposure of the rabbit eye to silicone oil causes optic nerve atrophy

A silicone oil endotamponade following vitrectomy has for decades been a standard method in human ophthalmology with a view to restoring a detached retina. However, severe functional deficiences may remain after treatment. In adult rabbits, the injection of silicone oil into the eye-ball following vitrectomy resulted in a decrease of 89% in the number of myelinated optic nerve fibres after a survival time of 1 year (418,313 ± 29,703 versus 45,620 ± 23,905). Concomitantly, the cross-sectional area of the optic nerve was also reduced significantly (0.853 ± 0.159 mm2 versus 0.355 ± 0.107 mm2). The number of non-neuronal elements of the optic nerve remained virtually unchanged immediately behind the eye-ball and in the middle part of the nerve, whereas it increased significantly close to the optic chiasm (3040 ± 433 versus 3888 ± 403). Thus, destruction of the myelinated optic nerve fibres is likely to be responsible for the functional deficiencies observed after silicone oil implantation.