WHAT ARE DIABETES AND DIABETIC RETINOPATHY?
Diabetes is a chronic, systemic disease in which the body does not use and store sugar properly. It results in many serious health problems; diabetic retinopathy is one of them. In this complication of diabetes, the eye’s light-sensitive retina is damaged because the system of blood vessels nourishing the retina is weakened. Fragile, new blood vessels form in the retina; these can then leak fluid into the retina, and bleed into the vitreous (the jellied, middle part of the eyeball). Both of these processes can be disastrous for vision.
Generally, diabetes is classified into two types: Type-1 (insulin-dependent) is an autoimmune disease that usually begins suddenly in late childhood or adolescence. Type-2 (non-insulin dependent) accounts for over 90 percent of diabetes cases in this country. Type-2 is no longer called “adult-onset diabetes” because this disease now affects increasing numbers of children.
WHO IS AT RISK FOR DIABETIC RETINOPATHY?
The short answer is that anyone with diabetes (either type) is at great risk of acquiring diabetic retinopathy. Nearly all diabetics who are treated with conventional methods of blood-sugar control get some early changes (called non-proliferative retinopathy) in their retinal blood vessels after several years. Many diabetics then proceed to symptomatic, proliferative diabetic retinopathy, in which abnormal, new blood vessels cause trouble. After living 40 years with the disease, about 60 percent of all diabetics have this potentially blinding complication.
WHAT ARE THE SYMPTOMS OF DIABETIC RETINOPATHY?
In the early, non-proliferative stage of diabetic retinopathy, the normal retinal blood vessels become weakened. This stage may not be noticed by the patient. However, in time, the weakened blood vessels can leak fluid and substances from the blood into the layers of the retina; this is called macular edema or swelling and can cause blurred central vision.
Besides weakened vessels, some of the cells making up the blood vessels can sicken and die. As more of this occurs, there is less oxygen and nutrition to the retina. The retina then produces factors that cause new growth (proliferation) of blood vessels, but these vessels do not grow appropriately. Instead of growing into the retina, they grow into the vitreous and can bleed, causing dark spots in the visual field that appear to move. Sometimes enough blood will impair the ability to see. In addition, the abnormal blood vessels can lead to scar tissue that detaches the retina.
Another common eye complication of diabetes is cataracts.
WHAT CAN BE DONE TO PREVENT OR MITIGATE DIABETIC RETINOPATHY?
No one can now prevent diabetes. However, there are ways to reduce the chance of developing type 2 diabetes. These include maintaining a healthy weight. Being overweight (having a body-mass index over 25) is a risk factor for diabetes, and being obese (BMI over 30) greatly increases the risk. If you weigh too much, then losing even one-tenth of your weight, and keeping it off, can significantly lower your chance of getting diabetes.
If you are overweight or obese, your doctor will test you periodically for a pre-diabetic condition called glucose intolerance. If this test is positive, then you will be under close supervision by a diabetes specialist and follow the doctor’s instructions.
If you already have diabetes, the best way to reduce the risk of complications, including diabetic retinopathy, is to keep your blood-sugar level in the normal range and work with your diabetic specialist to maintain a healthy “A1C level.” The A1C is a blood test that provides a number that relates to the average blood sugar over the previous three months.
If you have diabetes, it is recommended that you have your eyes examined for retinopathy every year. This requires dilation of the pupils and examination with special optical instruments. If you develop retinopathy, more frequent examinations will be recommended. Once a level of retinopathy occurs, then treatment can be done to preserve and sometimes improve visual acuity.
Pregnant women with diabetes should schedule an appointment in each trimester, as retinopathy can progress very quickly during pregnancy.
WHAT IS THE TREATMENT FOR DIABETIC RETINOPATHY?
The treatment of diabetic retinopathy is a success story for clinical research. Testing is usually performed before the decision to treat is made. These include fluorescein angiography, a photographic test using a fluorescent dye injected into a vein in the arm followed by numerous images, and optical coherence tomography (OCT), which provides an image of retinal layers and can detect macular edema. A laser treatment is effective in sealing off leaky vessels that cause macular edema.
In proliferative diabetic retinopathy, laser is performed in the part of the retina outside the macula and is called panretinal photocoagulation. There are also new treatments involving injections of a compound that inhibit the activity of the factors (vascular endothelial growth factor [VEGF], being one) that lead to macular edema or proliferative retinopathy. Several treatments may be necessary, over time, and sometimes are done in conjunction with vitrectomy surgery. A vitrectomy can be recommended to remove the blood-filled vitreous when it does not clear on its own or to remove membranes causing retinal detachment.
The treatment of diabetic cataracts is surgical removal, as in the case of age-related cataracts.
Much current research is directed at learning the biochemical pathways by which high blood sugar triggers the early pathological changes in the blood vessels of the retina, kidney, heart, and other essential organs. In the future, new, specific treatments could target biological signaling molecules and growth factors involved. There is also progress in developing anti-angiogenesis drugs aimed at inhibiting blood vessel growth.