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.

Early retinopathy

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.

Late retinopathy

The later stages of retinal injury are called proliferative retinopathy, because new fragile blood vessels grow to supply the damaged areas of the retina. These new blood vessels can bleed into the vitreous gel, the gel-filled area in front of the retina. Over time, scar tissue that forms from bleeding can cause the retina to detach from the wall of the eye (retinal detachment) and cause loss of vision.

Severe proliferative retinopathy may be treated with laser surgery in order to save vision. Your eye doctor may use more aggressive laser therapy, called scatter (pan-retinal) photocoagulation. This process is more thorough than that used in localized photocoagulation. And it may require more individual treatments. But it allows your doctor to minimize the growth of new blood vessels across the back of your retina. Severe proliferative retinopathy may also be treated with medicines that slow the growth of abnormal blood vessels in the retina. The growth of these vessels is triggered by a protein called vascular endothelial growth factor (VEGF). Anti-VEGF medicines, such as ranibizumab (Lucentis), block the effects of VEGF.

Laser treatments may not always work in treating proliferative retinopathy. If you have retinal detachment or hemorrhages that cannot be repaired, your retinal specialist will need to use a surgical technique to try to restore your vision. This surgical technique, called pars plana vitrectomy, attempts to repair your retina and reduce hemorrhaging. Like many surgical techniques, it has several risks and is much more likely to damage your eye than laser surgery.

Other eye problems

People who have diabetes are also at risk for other problems, such as cataracts and glaucoma, that damage vision. They are also at risk for a severe form of glaucoma called neovascular glaucoma. Cataracts are frequently caused by a lifetime of sun exposure, and diabetes speeds up their formation.

The following table outlines the major causes of blindness in people who have diabetes.

If you notice problems with your vision, you should immediately seek medical evaluation by an ophthalmologist. Regular eye exams are meant to detect any retinopathy at the nonproliferative stage, where it may still be treated with a good chance of success.

If nonproliferative retinopathy is not detected and treated early, it may progress to proliferative retinopathy. During proliferative retinopathy, your body tries to correct the microaneurysms. To replace blood vessels that have broken or leaked, new blood vessels begin to form. These blood vessels are fragile and may break easily, causing bleeding into the middle of the eye and clouding vision. They also form scar tissue that can pull on the retina and cause the retina to detach from the wall of the eye.

With aggressive management of your condition-keeping your blood sugar in your target range and controlling blood pressure-along with regular screening of your vision, you may be able to prevent or delay blindness.