• We evaluated the condition of a patient with chronic papilledema due to pseudotumor cerebri in whom a permanent, monocular, inferior, altitudinal, visual field defect suddenly developed. Clinical and fluorescein angiographic findings indicated that the loss of visual field was due to ischemic optic neuropathy. Ischemic optic neuropathy might occur in papilledema if the tissue pressure in the optic disc becomes sufficiently elevated to occlude the pressure-sensitive prelaminar arterioles.