Composite fluorescein angiogram of the retina of the left eye of a male patient where severe damage to the retina has been caused by diabetes (diabetic retinopathy). Blood vessels (grey) are seen emerging from the optic disc (centre left). The vessels have become blocked due to diabetes and have started to haemorrhage (bleed). This has caused a reduction in blood flow to other areas of the retina. Diabetic retinopathy may lead to blindness if left untreated. Bleeding can be treated by laser photocoagulation, and blood sugar level maintenance can slow the disease's progress.