A common complication of diabetes affecting the blood vessels in the retina (the thin light-sensitive membrane that covers the back of the eye). If untreated, it may lead to blindness. If diagnosed and treated promptly, blindness is usually preventable.

Diabetic retinopathy begins without any noticeable change in vision. But even then there often are extensive changes in the retina visible to an ophthalmologist (eye doctor). It is therefore important for a diabetic to have an eye examination at least once (ideally twice) a year.

There are two stages of diabetic retinopathy -- nonproliferative and proliferative retinopathy:

• Nonproliferative retinopathy is the earlier stage. In this stage there may be hemorrhages (bleeding) in the retina with leakage of blood causing a "wet retina" or protein deposits (exudates) in the retina. As a consequence, the retina does not receive enough oxygen. This early stage of diabetic retinopathy usually produces no visual symptoms but, if there is fluid in the central portion of the eye (macular edema), vision is diminished.

• Proliferative retinopathy is the second stage. New abnormal vessels develop in the retina and grow towards the center of the eye. These vessels frequently bleed into the vitreous (the clear jelly in the center of the eye). Such bleeding episodes cause severe visual problems. Small bleeds may clear up on their own but larger bleeds need surgery. The abnormal vessels may also produce large scars in the retina that may cause the underlying retina to detach (retinal detachment).