anterior ischemic optic neuropathy (MONDO_0006649, a Monarch Disease Ontology id) (AION) is an eye disease characterized by infarction of the optic disk leading to vision loss. It can be nonarteritic (nonarteritic anterior ischemic optic neuropathy or NAION) or arteritic, the latter being associated with giant cell arteritis (GCA; often termed temporal arteritis). Vision loss with both varieties is typically rapid (over minutes, hours, or days) and painless. Symptoms such as a general feeling of being unwell (malaise), muscle aches and pains, headaches over the temple, pain when combing hair, pain in the jaw after chewing, and tenderness over the temporal artery (one of the major arteries of the head) may be present with giant cell arteritis. At exam, visual acuity is reduced and the optic disk is swollen. In both subtypes, visual field examination is often reduced in the inferior and central visual fields. The visual loss is usually permanent, with some recovery possibly occurring within the first weeks or months. The arteritic variety is treated with corticosteroids. Treatment of the nonarteritic variety withaspirinor corticosteroids has not been helpful. Also known as: ischaemic optic neuropathy, ischemic optic neuropathy.