By Ivan G. Castillo, MD

November is National Diabetes Month. If you have diabetes mellitus, your body does not use and store glucose properly. Over time, diabetes can damage all of the blood vessels in the retina, including the arteries, veins, and capillaries.

The retina is the nerve layer at the back of the eye that senses light and helps to send images to the brain. The damage to the retina vessels is referred to as diabetic retinopathy. It causes the production of a chemical called vascular endothelial growth factor (VEGF) that worsens the damage of diabetic retinopathy.

Nonproliferative diabetic retinopathy (NPDR), commonly known as background retinopathy, is an early stage of diabetic retinopathy. In this stage, tiny blood vessels within the retina (the capillaries) leak blood and/or fluid and/or cholesterol. The leaking blood causes hemorrhages in the retina, and the leaking fluid can cause the retina to swell, resulting in edema. The leaking cholesterol causes the formation of deposits called exudates.

Many people with diabetes have mild NPDR, which usually does not affect their vision. When vision is affected, it is the result of macular edema or macular ischemia, or both.

Macular Edema
Macular edema is swelling or thickening of the macula, a small area in the center of the retina that allows us to see fine details clearly. The swelling is caused by fluid leaking from the damaged retinal capillaries. It is the most common cause of visual loss in diabetes. Vision loss may be mild to severe, but even in the worst cases, peripheral (side) vision continues to function. The injection of anti-VEGF medication into the eye can be used to help control vision loss from macular edema. Laser treatment can be used in combination with the anti-VEGF medication injections.

Macular Ischemia
Macular ischemia occurs when small blood vessels (capillaries) close completely. Vision blurs because the macula no longer receives sufficient blood supply to work properly. Unfortunately, there are no effective treatments for macular ischemia.

Detecting Nonproliferative Diabetic Retinopathy (NPDR)
The retinal capillaries may be badly injured before there is any change in vision. A medical eye examination is the only way to discover any changes inside your eye. If your ophthalmologist finds diabetic retinopathy, he or she may order color photographs of the retina — a special test called fluorescein angiography — or optical coherence tomography (OCT) to find out if you need treatment. During a fluorescein angiography, a vegetable-based dye is injected into a vein in the arm. The flow of the dye through the retinal capillaries is then recorded by a series of photographs.

Protecting Your Vision
If you have diabetes, early detection of diabetic retinopathy is the best protection against loss of vision. You can significantly lower your risk of vision loss by maintaining strict control of your blood glucose and visiting your ophthalmologist regularly. People with diabetes should schedule comprehensive eye examinations at least once a year. Pregnant women with diabetes should schedule an appointment in their first trimester, because retinopathy can progress quickly during pregnancy. More frequent medical eye examinations may be necessary after a diagnosis of diabetic retinopathy.