Objective: To study the histopathological changes in the optic nerve following posterior insertion of a glaucoma drainage device.

Methods: The Ahmed glaucoma valve (AGV) (model no. S-3) was inserted 10 to 12 mm behind the limbus in the superotemporal quadrant of the rabbit eye. One eye of six albino New Zealand rabbits was randomly assigned to the AGV group. At the end of two months, the enucleated eyes were examined histologically for optic nerve changes.

Results: The fibrous capsule around the endplates involved the optic nerve in all eyes in the AGV group. The endplate was found to be either in contact (4 eyes) or within 1 mm from the optic nerve (2 eyes) in all six eyes. Histopathological examination of the optic nerves in the AGV group with optic nerve contact exhibited microglial loss, astrocyte clustering, and fibrillary changes. The two eyes in which the end-plate was within 1mm (but no physical contact) with the optic nerve showed only early vacuolization of the astrocytes. No such changes were noticed in the control eyes.

Conclusions: The rabbit model demonstrates the potential for optic nerve damage when the AGV end-plate is inserted within 1 mm of the optic nerve.