Diabetic retinopathy is the leading cause of blindness in people aged 20-74 years, accounting for 8% of all cases of legal blindness and 12% of the newly blind (Klein 1995). A common complication of all forms of diabetes mellitus, diabetic retinopathy is present in over 2.5% of the U.S. population, or more than 5.3 million people aged 18 or older (Prevent Blindness American 2002).