The investigation of patients with retinal artery occlusion, retinal vein occlusion and cotton wool spots is discussed. The majority are due to either emboli or atheroma and occur in elderly patients. A full clinical history and examination remain the essential part of the investigation but the ophthalmologist must select patients in whom further investigation is warranted. The recent recognition of the importance of antiphospholipid antibodies and natural anticoagulant deficiency states in the pathogenesis of thrombosis has identified a group of young people in whom specific therapy may be indicated.