Definition of Diabetic retinopathy

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Diabetic retinopathy: 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).

The diagnosis of diabetic retinopathy is made by a dilated retinal examination (eye exam after the eyes are dilated). This may be coupled with a fundus fluorescein angiography, a test done to assess the extent and type of changes in the retina and its blood vessels. In this test a small amount of dye is injected into a vein in the arm and pictures are taken of the eye. Usually this test is done as an outpatient procedure.

Treatment is by laser surgery, usually also on an outpatient basis. The nature of the laser treatment depends on the stage of the retinopathy:

• In the early nonproliferative stage, the laser is used to treat the leaking blood vessels. The laser produces a small scar that helps seal the leak. This is called as focal laser therapy.
• In the later proliferative stage, the laser is used to produce many small burns all around the edge of the retina. The aim is to produce disappearance of the new vessels. This is done by increasing the oxygen supply to the retina. This procedure is called panretinal photocoagulation.

Laser therapy can only stop the progression of diabetic retinopathy. It cannot reverse the damage already done. The progression of the retinopathy can be slowed down by careful control of the diabetes, effective reduction of high blood pressure together with regular eye exams and, if needed, prompt laser therapy.