Pathology of Ischemic Optic Neuropathy

Ischemic optic neuropathy (ION) describes a state of hypoxic injury of the optic nerve. Clinically, ION is divided into anterior and posterior forms defined by the presence or absence of optic disc swelling, respectively. It is further classified as arteritic when secondary to vasculitis, and nonarteritic when not. The site of vascular occlusion for anterior ION from giant cell arteritis is the short posterior ciliary arteries, but mechanical vascular obstruction does not play a role in most nonarteritic cases. Histologically, ION is characterized by axon and glial necrosis, edema, and a sparse mononuclear response. Like other ischemic injuries, the morphologic alternations in the nerve are time dependent. A variant of ION called cavernous degeneration (of Schnabel) features large cystic spaces filled with mucin. Several conditions can histologically mimic cavernous degeneration of the optic nerve. The scarcity of cases of ION examined histologically has contributed to an incomplete understanding of its pathogenesis.