One of the most frequent causes of vision impairment in the United States and throughout the rest of the world is diabetic retinopathy. Diabetic retinopathy is a complication of diabetes that causes damage to the blood vessels of the retina – the light-sensitive tissue that lines the back part of the eye, allowing you to see fine detail. Diabetic retinopathy occurs in more than half of the people who develop diabetes. The longer you have diabetes, and the less controlled your blood sugar is, the more likely the possibility that you will develop diabetic retinopathy.
There are generally two causes of vision loss from diabetic retinopathy – diabetic macular edema and proliferative diabetic retinopathy.
- Diabetic macular edema. Diabetic macular edema is the term used for swelling in the central part of the retina. The macula, or center part, of the retina is used for sharp, straight-ahead vision. It is nourished by blood vessels that become affected by diabetes. The blood vessels are weakened by diabetes and may become leaky. This causes the retina to become thickened or swollen. This swelling of the central part of the retina can lead to decreased vision.
- Proliferative diabetic retinopathy. Diabetes can cause damage to the small blood vessels in the retina, resulting in poor circulation to the retina. Vision may be lost because some of the retina tissue may die as a result of this inadequate blood supply. Unlike skin tissue, which might grow back if it is lost, retina tissue is like brain tissue and does not grow back once it is lost. Furthermore, the poor circulation may lead to the development of growth factors that can cause new blood vessels and scar tissue to grow on the surface of the retina. This stage of diabetic retinopathy is called proliferative diabetic retinopathy (PDR). It is referred to as “proliferative” because at this stage of the disease, new, abnormal blood vessels and scar tissue begin to grow on the surface of the retina. The vessels bleed into the middle cavity of the eye, causing vision loss because light cannot reach the retina. In addition, the scar tissue formation can pull on the retina and cause vision loss by detaching the retina from the back of the eye. Occasionally, these blood vessels and scar tissue may grow in the front of the eye, where fluid normally exits. When the fluid cannot escape, pressure can build in the eye, creating a rare type of glaucoma (neovascular glaucoma) that can damage the vision even further and cause the eye to become painful.
It is possible to have diabetic retinopathy for a long time without noticing symptoms. Often, diabetic retinopathy will cause symptoms unnoticeable to a patient until substantial damage already has occurred.
Diabetic retinopathy usually affects both eyes. Symptoms may include blurred or double vision, difficulty reading, or the appearance of spots – known as “floaters” – in your vision. You also may notice a shadow across your field of vision, pain or pressure in your eyes, or difficulty with color perception. Some patients may experience a partial or total loss of vision.
The primary cause of diabetic retinopathy is diabetes – a condition in which the levels of glucose (sugar) in your blood are too high. Elevated sugar levels from diabetes can damage the small blood vessels that nourish the retina, and may in some cases block them completely. As a result, the blood supply to the retina from these damaged blood vessels is cut off, and vision is affected.
As mentioned above, in response to the lack of blood supply the eye may create growth factors that cause leakage of blood vessels that result in swelling of the retina (diabetic macular edema) or growth of new blood vessels and scar tissue (proliferative diabetic retinopathy). These new blood vessels can bleed into the middle cavity of the eye, and the scar tissue can pull on the retina — sometimes, leading to vision loss if the retina detaches from the back wall of the eye.
Anyone who has diabetes is at risk of developing diabetic retinopathy. There are, however, additional factors that can increase your risk.
One of the most important factors is the duration of your diabetes. The longer you have had it, the greater your risk of developing diabetic retinopathy. Another key factor is how well you have controlled your blood sugar level over time. Another factor that can influence the control of your blood sugar level and the subsequent development of diabetic retinopathy is high blood pressure. It also is possible that cholesterol levels can have an effect on this process, and pregnancy in someone with diabetes can result in changes in the retina as well.
People with type 2 diabetes who use certain prescription medicines, such as pioglitazone and rosiglitazone, to treat their diabetes may be at greater risk for problems with the center of the retina (the macula). The U.S. Food and Drug Administration (FDA) has warned that taking some medicines could cause swelling in the macula, a condition known as macular edema. Check with your physician for more information about prescription medications that could put you at risk.