Diabetic retinopathy is a disease of the retina, the thin tissue that lines the back of the eye. The condition is a complication of diabetes; it is related to high blood sugar levels, which interfere with oxygen delivery to the cells in the retina.

Nerve cells in the retina detect light entering the eye and send signals to the brain, which interprets what the eye sees. Damage to the retina from a lack of oxygen to its nerve cells may not be noticed right away. If the disease progresses, however, it can cause gradual vision loss. Both eyes are usually affected by the disease.

The early form of the disease, called nonproliferative diabetic retinopathy, develops when diabetes weakens the tiny blood vessels that supply the retina, causing swelling or deposits to form on the retina. Changes caused by nonproliferative retinopathy may not affect vision unless fluid and protein from the damaged blood vessels cause swelling in the center of the retina (macula). This condition, called macular edema, can cause severely blurred or distorted central vision.

Proliferative diabetic retinopathy is the advanced form of diabetic retinopathy. The main feature of proliferative retinopathy is the growth of fragile new blood vessels on the surface of the retina. These blood vessels may break easily, bleeding into the middle of the eye and clouding vision. They also form scar tissue that can pull on the retina, causing the retina to detach from the wall of the eye (retinal detachment).

People who have diabetes need regular eye exams so that the early stages of diabetic retinopathy can be detected and, in some cases, treated. Blood sugar levels should also be monitored and controlled as much as possible to prevent blood vessel damage.