Non-arteritic anterior ischaemic optic neuropathy: a review and update.

Non-arteritic anterior ischaemic optic neuropathy (NAION) is the most common acute optic neuropathy in people aged 50 years and older. The condition is caused by infarction of the laminar or retrolaminar portion of the optic nerve head supplied by the short posterior ciliary arteries (SPCAs). The underlying aetiology and pathophysiology is poorly elucidated. Factors that have been implicated include nocturnal hypotension, impaired autoregulation of the microvascular supply, vasculopathic occlusion, and venous insufficiency. These factors are thought to result in axonal oedema causing a compartment syndrome in a structurally crowded optic disc leading to axonal degeneration and loss of retinal ganglion cells via apoptosis. Clinically NAION is characterised by sudden, usually painless, loss of vision in one or both eyes. Examination findings include decreased visual acuity, a visual field defect, decreased colour vision, a relative afferent pupillary defect, and optic disc swelling. Despite significant research, treatment options for NAION remain limited.