Swelling of the region where the optic nerve joins the retina (the thin light-sensitive area in the back of the eye). Because of swelling, the optic disc looks “angry” (inflamed and swollen), its margins become blurred and hard to distinguish, and the small cup in the center of the disc decreases in size. Optic disc edema is a sign of possible serious disease. If unilateral (in one eye only), possible causes include ischemic optic neuropathy, central retinal vein occlusion, and orbital optic nerve tumors. If caused by increased intracranial pressure and both eyes are involved, the condition is called papilledema. This can result from a brain tumor, bleeding into the brain tissue, and pseudotumor cerebri. Malignant hypertension may also cause bilateral disc swelling.