Retinopathy is a "silent" disease of the back of the eye - it has no symptoms in its early stage. A person with retinopathy could have it for years with no pain or other symptoms until the condition progresses enough to cause vision loss. It is usually caused by diabetes, and with treatment, vision loss may be slowed or halted.

There are two main types of diabetic retinopathy: non-proliferative and proliferative.

Non-proliferative diabetic retinopathy is characterized by leakage from small retinal blood vessels (capillaries). This leakage permits protein to accumulate in the retina causing the retina to become swollen or "waterlogged" . If this swelling occurs in the macula (area of central vision), sight may be significantly diminished. Retinal capillaries may also become closed off resulting in poor retinal nutrition. Loss of circulation to the macula can result in severe loss of central vision.

Proliferative diabetic retinopathy occurs when widespread impairment of retinal nutrition results from capillary leakage and closure. The poorly nourished retina then sends out some type of chemical distress signal that causes new blood vessels to bud and grow (proliferate) on the retinal surface. Unfortunately these new blood vessels are very fragile and usually rupture, permitting bleeding to occur within the eye. Scar tissue may grow around the abnormal blood vessels and lead to pulling on the retina, causing retinal detachment and possible permanent blindness. The proliferative form of diabetic retinopathy is present in approximately 20% of patients with diabetes of ten years' duration.