In diabetes, there is too much sugar in the blood. When the blood sugar is constantly or frequently high, many complications occur: eyesight can suffer, heart attacks and other blood vessel problems can occur, and one's life-span can be shortened. When the blood sugar is maintained at a normal level, at or below 126, the complications of diabetes, including serious diabetic retinopathy, can be reduced. Controlling blood sugar is the single most important thing a person with diabetes can do to prevent the complications of diabetes and diabetic retinopathy.

Type I diabetes usually begins at a young age. People with type I diabetes must take insulin to survive and to control blood sugar. Most people with type I diabetes take an intermediate-acting type of insulin (such as human NPH or Lente) or a long-acting type of insulin (such as human Ultralente) to drive a small, constant level of insulin throughout the day. In addition, they often take regular human insulin before meals to control the rise in blood sugar that occurs with meals. Some people with diabetes wear insulin pumps. People with type I diabetes should test their own blood sugar with a glucometer (a glucose-monitoring device) several times daily so they can adjust their diet, exercise, and insulin doses to keep the blood sugar level below 150 and above 60 at all times. They should follow a diet controlled in carbohydrates and low in fat and cholesterol. Regular exercise is also very important as it helps reduce blood sugar.

Type II diabetes usually starts in adult life and is often not dependent on insulin for control of blood sugar. Maintaining normal weight and a diet low in calories, fat, and cholesterol is very important. Blood sugar can be controlled either with diet alone or in combination with pills to lower blood sugar. In some cases, insulin treatment is also necessary.

All people with diabetes should see a general physician, internist, or endocrinologist, who has knowledge of the important ways to help with diabetes strictly control their blood sugar. The doctor will probably measure the patient's glycohemoglobin (which reflects the average blood sugar level for the past two months) several times yearly.

In addition to the importance of diet and exercise, there are other factors that can affect diabetes. High blood pressure is very bad for people with diabetes because it increase the likelihood of complications, including loss of vision. Blood pressure should be strictly controlled and kept normal if at all possible. Smoking is known to be particularly bad for people with diabetes because it promotes the closure of blood vessels.

Finally, the severity of diabetic retinopathy is often related to the length of time the person has had diabetes. It is unusual for someone with type I diabetes to have significant diabetic retinopathy during the first 10 years of the disease. After 10 years, and especially after 20 years, most people with type I diabetes have some retinopathy, although it may not be severe, especially if the blood sugar level has been well controlled. In people with type II diabetes, the diabetic retinopathy may be discovered shortly after, or sometimes even before, the diabetes is diagnosed.

All people with diabetes, especially those who have had diabetes a long time, should have regular eye examinations (particularly examinations of the retina, through a dilated pupil) to be sure that diabetic retinopathy is not developing.