How Diabetes Causes Blindness - Topic Overview
Over time, high blood sugar levels from diabetes lead to damage of the retina, the layer on the back of the eye that captures images and sends them as nerve signals to the brain. Whether diabetic retinopathy develops depends in part on how high blood sugar levels have been and how long they have been above a target range. Other things that may increase your risk for diabetic retinopathy include high blood pressure, pregnancy, a family history of the condition, kidney disease, high cholesterol, and whether you smoke.
The early stages of retinal damage are called nonproliferative retinopathy. First, tiny blood vessels called capillaries in the retina develop weakened areas in their walls called microaneurysms. When red blood cells escape through these weakened walls, tiny amounts of bleeding (hemorrhages) become visible when the retina is viewed through an instrument called an ophthalmoscope. To clearly see your retina, the ophthalmologist will enlarge (dilate) your pupils (which serve as a window to the back of your eye) and may also use a special dye to help identify blood vessels that may be leaking.
Fluid from the blood also escapes, leading to yellowish "hard exudates." This type of damage does not cause problems with vision unless some of the leaking fluid is near the macula. (The macula is the area of the retina that is responsible for central vision.) An ophthalmologist who specializes in the treatment of retinal problems will attempt to stop blood leakage by using a laser in a process called photocoagulation. By using an appropriately selected laser, your ophthalmologist may seal the small blood vessels that can leak when a person has nonproliferative and proliferative retinopathy. More recently, ophthalmologists have been using injectable medicines to treat retinal leakage.
If fluid leaks out near the macula, it can disrupt vision. This is called macular edema. As retinopathy becomes more severe, parts of the abnormal capillaries can become closed off. This kills parts of the retina that the capillaries previously supplied with blood. These tiny damaged parts of the retina are called "cotton wool" spots and can be seen using an ophthalmoscope.