The Facts About Diabetes Eye Disease

By David S.H. Bell, MD, MB, FACE, FACP

One of the most feared complications of diabetes is blindness from diabetes-related vision loss, or diabetic retinopathy. Retinopathy involves changes to blood vessels in the retina, the light-sensitive nerve layer at the back of the eye that contains cells that trigger nerve impulses that pass via the optic nerve to the brain, where a visual image is formed. The changes in the blood vessels can cause them to bleed or leak fluid, resulting in distorted vision. This is caused by prolonged hyperglycemia (high blood glucose levels). With high glucose levels, the cells that surround and support the small blood vessels of the retina are lost, which leads to the following problems:

  • Microaneurysms Microaneurysms are caused when the lining of the blood vessels bulges through the blood vessel wall. Microaneurysms are key in diagnosing diabetic retinopathy, but do not cause visual loss.
  • Exudates These are a mass of cells and fluids caused by leakage of fluid, protein and fats from the blood vessels. Exudates do not interfere with vision unless the leakage occurs in the macula (macular edema), an oval-shaped, yellowish area near the center of the retina. It is the only part of the retina with 20/20 vision, so swelling in this region interferes with vision.
  • Retinal Infarcts Infarcts – small, localized areas of dead tissue – occur when there is a poor blood supply to the retina which results in the death of multiple small parts of the retina. They appear as yellow exudates and are most likely to result in vision loss when an infarction occurs near the optic nerve.
  • New Vessel Growth A lack of nutrients, especially oxygen, to the remaining retina causes the formation of new vessels in an attempt to restore retinal oxygenation. New vessels are formed due to the release of Vascular Endothelial Growth Factor (VEGF), a protein produced by cells to stimulate new blood vessels. These thin-walled blood vessels grow into the vitreous gel, the clear gel that fills the space between the lens of the eye and the retina, and can rupture and bleed into the vitreous. The resultant hemorrhage absorbs the light entering the eye so that light does not reach the retina and vision is lost. Also, these vessels are surrounded by fibrous (scar) tissue which can contract, putting traction on the retina and separating the retinal layers, which can result in loss of vision. If these vessels grow as far forward as the iris (the colored part of the eye), the eye’s drainage ducts may get blocked and result in increased pressure within the eye (glaucoma).

How to avoid diabetic retinopathy

First and foremost, retinopathy can be avoided through blood sugar control.

In the Diabetes Control and Complications Trial, a major, 10-year clinical study that compared good glycemic (blood sugar) control (average HbA1c of 7.2 percent, or an average blood sugar of about 155) with poor glycemic control (average HbA1c of 8.0 percent, or an average blood sugar of about 180), participants that had type 1 diabetes, the diabetes that occurs when one’s own antibodies interfere with the production of insulin, showed a 44 percent lower risk of developing retinopathy than in those with the higher HbA1c.

The United Kingdom Prospective Diabetes Study, the largest study ever performed of type 2 diabetes (the type of diabetes caused by your body not using insulin properly plus producing less insulin over time) showed that those who had an average HbA1c of 7 percent (average blood sugar of 150) had 25 percent less retinopathy than those with an average HbA1c of 7.9 percent (average blood sugar just under 180). Even in those with better glycemic control, if some eye changes were already present, there was a decreased need for pan-retinal photocoagulation laser therapy, a procedure in which a laser beam is used to destroy all of the dead areas of retina where blood vessels have been closed. When these areas are treated with the laser, the retina stops manufacturing new blood vessels, and those that are already present tend to decrease or disappear. As these abnormal vessels disappear, the risk of vitreous hemorrhage and retinal detachment are reduced.

Lowering blood pressure also decreases the risk of developing retinopathy; studies suggest avoiding tobacco use will also help. And while exercise is encouraged to help control glucose levels, straining such as occurs when lifting weights may cause bleeding and should be avoided in those with advanced retinopathy.

Detecting diabetic retinopathy

If you are over 10 years old or have had type 1 diabetes for more than five years, or if you have type 2 diabetes, you need an annual eye exam including dilation performed by an ophthalmologist or an optometrist – both specialists in the exam of the eye. This usually means that you will have drops put into the eye to open or enlarge the central black area of the eye, the pupil, allowing the doctor to better see the nerves and blood vessels in the back of the eye. An examination through a non-dilated pupil is not acceptable because many areas of the retina cannot be visualized without pupil dilation. Retinal photography through a non-dilated pupil with the photographs being read by an ophthalmologist is only acceptable as a screening tool. If the ophthalmologist discovers retinopathy on a retinal photograph, an examination through a dilated pupil is necessary.

Since retinopathy may worsen during pregnancy, it is recommended that a retinal examination be performed before pregnancy as well as during the first trimester (first three months) of pregnancy. Not all optometrists are trained in the ability to perform a diabetes eye exam, so be specific when you schedule your appointment that you need this specialized type of exam.

Treating diabetic retinopathy

If or when diabetic retinopathy occurs, it is very treatable, especially if detected at an early stage. Once the diagnosis of diabetic retinopathy is made, management of the condition should be provided by an ophthalmologist, preferably a retinal specialist who treats any condition that affects the retina, the light-sensitive area at the back of the eye that contains the structures responsible for clear, sharp vision. These specialists also treat problems within the vitreous, the jelly-like material that forms the eye’s shape, and diseases that affect the optic nerve, which carries visual signals to the brain.

If leakage in the macular area (called macular edema) or growth of new blood vessels occurs (proliferative retinopathy), then intervention with photocoagulation or anti-VEGF injected into the vitreous gel is needed.

Pan-retinal photocoagulation (laser therapy) reduces the area of retinal tissue that is not receiving enough oxygen so that the surviving retinal tissue will have sufficient oxygen. Well-oxygenated tissue will not produce VEGF, which stops the growth of abnormal new vessels. Key areas for vision such as the optic nerve and macula are avoided during laser therapy. While central vision is maintained, laser therapy comes with the price of night vision and color vision loss and decreased peripheral (side) vision.

More recently an alternative to laser therapy has been developed with drugs that are called inhibitors of VEGF. These drugs are injected into the central fluid portion of your eye and counteract effects of VEGF by decreasing leakage from and growth of abnormal blood vessels. Very recently the use of these drugs (ranibizumab, aflibercept, bevacizumab and pegaptanib) has been shown to be just as effective as traditional laser therapy.

Occasionally surgery is needed to restore as much vision as possible. Surgery can repair a retinal detachment, where the retina is separated from the wall of the eye, or remove a hemorrhage in the fluid portion of the eye that is blocking passage of light to the cells that are responsible for sight. To treat a hemorrhage in the fluid of the eye, the fluid is removed and replaced with a salt and water solution. Often an air bubble to “splint” the reattached layers of the retina is inserted. If symptoms of retinal detachment (appearance of dark specks, dots, strings or globs) or any visual loss occurs, notify your ophthalmologist or retina specialist immediately. Medical attention should be obtained promptly since repair of the retina must take place within one to two days to be successful.

Anyone who has diabetes can develop diabetic retinopathy. And while surgery can slow or stop the progression of the disease, it’s not a cure. Because diabetes is a lifelong disease, future retinal damage and vision loss are still possible. The good news is that researchers are studying new treatments for the disease that may help.

Researchers at the National Institute of Health’s (NIH) National Eye Institute are seeking ways to detect diabetic retinopathy at earlier stages. For example, a technology called adaptive optics, developed by astronomers to improve the resolution of their telescopes by filtering out atmospheric distortions, is being studied to determine if it can improve the detection of subtle changes in retinal tissue and blood vessels. And other medical centers across the country are studying new, innovative treatments for diabetic retinopathy, including medications that may help prevent abnormal blood vessels from forming in the eye. These treatments appear promising, but more study is needed.

Meanwhile, you can help reduce your risk of vision loss by taking your diabetes medication as prescribed, keeping a healthy weight, controlling your blood pressure, cholesterol and blood sugar levels and, if you smoke, kicking the habit.

Dr. David S.H. Bell, MB, FACE, FACP is a retired Professor of Medicine and board certified endocrinologist practicing in Mountain Brook, AL. He has written over 340 articles for referred medical journals and was honored in 2004 by the American College of Endocrinology with the Outstanding Clinical Endocrinologist award.