There are two acute ischemic processes of the optic nerve. Vascular pseudopapillitis or ischemic optic neuropathy is characterized by a palid papilledema, followed by an optic atrophy, by a reduction of the visual acuity and fascicular defects of the visual field. Arteritis temporalis is characterized by the same ophthalmologic signs and by a raised erythrocyte sedimentation rate. Histologic examination of the temporal artery permits not only the diagnosis, but also the differentiation between the two diseases, which are due to an involvement of the short posterior ciliary arteries or of the central vascular system or pial system of the optic nerve head.