DR is the most common diabetic eye disease and is the leading cause of blindness in adults in the United States. It is caused by damage to the blood vessels of the retina, which is the light-sensitive outer layer of the eye. Retinal blood vessels are often affected by the high blood sugar levels associated with diabetes. Older people have an increased risk of developing DR; however, DR is likely to occur earlier and be more severe in anyone who has poorly controlled diabetes. Almost everyone who has had diabetes for more than 30 years will eventually show signs of DR. Symptoms of DR include poor night vision, seeing spots in front of the eyes, blurred vision, and blindness. The ACCORD study is a study that is examining the effects of different treatments on cardiovascular disease in people with diabetes. Participants in the ACCORD study will receive one of eight different combinations of treatment, including blood sugar control, blood pressure control, and cholesterol-controlling medication. This study will enroll participants in the ACCORD study and will examine the effects of the study treatments on DR. The results from this study may be used to develop new treatments to help prevent diabetes-related blindness.