Simulation of vision in diabetic retinopathy. This view of activities in Regent's Street, London is occluded by dark patches, which represent the retinal deposits & haemorrhages that occur in diabetic retinopathy. Retinopathy, the damage to the blood supply of the retina, occurs in diabetes when the disease is poorly controlled. The blockage of small arteries & capillaries causes a reduction or cessation in blood supply to some areas of the retina. In addition, increased permeability of the blood vessels underlies the development of haemorrhages, fatty exudates and oedema - all of which damage the retina & threaten sight.