Ischemic optic neuropathy (ION) is the most frequent optic neuropathy in patients older than 50. Anterior ION is classified as nonarteritic, especially in patients with vasculopathic risk factors and/or small optic disc, or arteritic. Monocular visual loss is usually sudden. Typical exam findings are optic nerve swelling and altitudinal visual field defect. Clinical profile, sedimentation rate, and especially fluorescein angiography are very useful to make the distinction between nonarteritic and arteritic ION. Treatment of temporal arteritis with steroids is an emergency but there is no effective therapy of the nonarteritic form.