Diabetes is a disease in which the body does not produce or properly use insulin. Insulin is a hormone that is needed to convert sugar, starches and other food into energy needed for daily life. Diabetes can affect the eye in a number of ways. The most serious eye condition associated with diabetes involves the retina, and, more specifically, the network of blood vessels lying within it. Diabetes can damage blood vessels and nerves and decrease the body's ability to fight infection. You may not notice a foot injury until an infection develops.