Non-arteritic ischemic optic neuropathy (NAION) is virtually unknown outside ophthalmology. It is characterised by acute unilateral visual loss, no pain on eye movements and virtually always optic disc swelling. Optic disc oedema resolves within 1 to 2 months, leaving behind optic atrophy. Vision hardly improves. NAION is the product of local abnormalities of the vascular supply to the optic nerve and general vascular risk factors. Of these, diabetes, hypertension and especially sleep apnoea syndrome are the most important. Recurrences in the involved eye are rare; contralateral recurrence occurs in approximately 15 % of patients. There is no clear scientific evidence for any specific therapy. However, there is general agreement that it is reasonable to control risk factors.