There are two basic kinds of diabetes. Type 1 diabetes is diagnosed early in life and requires insulin to bring the glucose level down to normal. Type 2 diabetes occurs later in life, and can be controlled with diet, pills, or insulin, depending on its severity.
Diabetes primarily affects the blood vessels that nourish the retina.
The retinal vessels work like a garden hose, bringing oxygen and other nutrients into and out of the eye. Diabetes can also make the blood vessels close off. These new vessels do not help the eye, however. They are fragile and can cause blindness by hemorrhaging or retinal detachment. Diabetic retinopathy develops gradually over many years.