Diabetic retinopathy is a vision-threatening complication of diabetes mellitus that is marked by changes in the blood vessels in the retina, the light-sensitive tissue at the back of the eye. These changes occur over time owing to high blood sugar levels, which cause the walls of the blood vessels that supply blood to the retina to become thicker. Initially, this causes the blood vessels to become more porous, or leaky. Leakage of fluid, blood, and lipid (fat) may accumulate in the center of the retina, or macula, leading to blurred vision (diabetic macular edema). In later stages of diabetic retinopathy, small blood vessels in the retina close, depriving the tissue of food and oxygen (ischemia). This fosters the release of a vasoproliferative substance inside the eye, which causes new, abnormal blood vessels to proliferate (a condition referred to as neovascularization).
Diabetic retinopathy is the leading cause of blindness in Americans age 20 to 65. However, regular eye exams and timely treatment can prevent or retard visual impairment associated with the condition.
In the early stages of diabetic retinopathy, termed nonproliferative retinopathy, the tiny blood vessels in the retina develop outpouchings, called micro-aneurysms. These bulges, in conjunction with leaking capillaries, may leak blood or fluid anywhere in the retina. If this fluid builds up in the macula, central fine vision becomes altered. If fluid buildup becomes severe, and if both eyes are affected, reading and driving vision may be lost.
Advanced nonproliferative retinopathy may subsequently develop. This stage of the condition is caused by decreased blood flow within the retina and is marked by a number of additional changes. These include venous beading, which causes veins to resemble a string of beads owing to localized areas of dilation and constriction in the vessels. Intraretinal microvascular abnormalities (IRMA) refer to abnormal, spaghetti-shaped blood vessels that run between the normal vessels in the retina; multiple areas of these vessels predict progression to proliferative retinopathy. Another change is the development of cotton wool spots-areas of swollen nerve tissue that appear like white clouds on the retina and are the result of cell death from blocked blood capillaries.
Proliferative retinopathy, the most advanced stage of diabetic retinopathy, is marked by the spontaneous growth of new blood vessels, which are more fragile than the normal retinal blood vessels and are more prone to breaking and bleeding. These vessels are accompanied by fibrous scarring and this fibrovascular tissue grows out of the retina itself and into the vitreous humor (the gellike substance that fills the eyeball). Blindness can occur if these vessels bleed (vitreous hemorrhage) or pull on the retina, causing a retinal detachment. Similar fibrovascular tissue may develop in the front of the eye on the colored iris. This, too, can cause blindness due to neovascular glaucoma.
