Particularly in patients over 40 years of age, disturbances of perfusion at the optic nerve head and retina are a frequent cause of acute visual acuity loss. As the most important disease entities, we must distinguish between ischemic optic neuropathy and arterial and venous perfusion disturbances. The prognosis with regard to visual acuity is, at any rate, serious: a considerable, persistent loss of vision must be expected. Unfortunately, at present there is no therapy available which could normalize perfusion quickly enough. In individual cases of ocular venous thrombosis, isovolumetric hemodilution can be effective. Use of argon-laser coagulation may markedly reduce the occurrence of severe complications (hemorrhagic glaucoma, vitreous bleeding). As an emergency measure, brief massage of the globe as well as administration of 100 mg prednisone and 250 mg acetazolamide are recommended. Disturbances in ocular perfusion call investigation with regard to hematological and vascular risk factors. It is always important to rule out giant-cell arteritis (Horton's disease).