Ischemic optic neuropathy is caused by ischemia of the optic nerve head in the region of the lamina cribrosa. Differentiation is made between arteritic (AION) and nonarteritic (NAION) forms. AION is the most common ophthalmological manifestation of giant cell arteritis and is usually well controlled with systemic steroid therapy. Temporal artery biopsy for confirmation of the diagnosis is mandatory. NAION is not a disease entity but rather the common pathogenetic pathway of a large variety of diseases and conditions and is often the result of several interacting factors. For this reason, there is no "standard therapy" for NAION. Careful interdisciplinary work up in NAION frequently reveals previously unrecognized diseases requiring treatment according to internal medicine standards. Adequate treatment frequently results in improvement of the affected eye and reduced risk of NAION in the other eye or of brain infarction.