Diabetic retinopathy can take two forms, background retinopathy and proliferative retinopathy. During the early stage of the disease (background retinopathy), small blood vessels in the retina leak a clear fluid (serum) into the surrounding tissue which causes swelling. Abnormal blood vessels may also hemorrhage or leak fats and proteins which form deposits. If fluid collects in the macula, diminished or blurred vision will result. However, if leakage or deposits occur in the outer edges of the retina, no symptoms may be noticed.
Sight is not usually seriously affected in cases of background retinopathy. In fact, the condition does not progress in 80% of patients. However, background retinopathy is a warning sign and can progress into the more serious stage of the disease, proliferative retinopathy.