Loss of vision among diabetics results from two primary conditions: diabetic retinopathy and diabetic macular edema. In diabetic retinopathy, tiny blood vessels in the retina become damaged, Joslin officials said. While early in the disease there are often no symptoms, over time new, abnormal blood vessels proliferate and bleed easily. If untreated, proliferative diabetic retinopathy can cause severe vision loss.

In diabetic macular edema, leaky blood vessels cause swelling in the macula -- the part of the retina responsible for central vision.