Diabetes Control Slows Retinopathy

Diabetic retinopathy is the most common cause of moderate and severe vision loss in working-age Americans.

It is a major public health problem now, and it will become even more so as the incidence of type 2 diabetes increases, says Dr. Peter Campochiaro, a professor of ophthalmology and neuroscience at the Wilmer Eye Institute at Johns Hopkins.

• Obesity predisposes people to type 2 diabetes, and thus, to retinopathy. A healthy diet and regular exercise help reduce obesity and the risk of diabetes.

• The chances of developing diabetic retinopathy increase with the duration of diabetes. Strict control of blood sugar level can forestall or prevent it. People with diabetes should keep track of their HbA1, which is the best measure of average blood sugar level over the preceding few months.

• Prolonged high blood sugar damages retinal blood vessels, resulting in hemorrhages and small aneurysms, the first signs of diabetic retinopathy. Diabetic patients need yearly retinal examinations to detect these changes. Finding them means that repeat exams are needed at least every six months. Continued damage might close retinal blood vessels, leaving the affected part of the retina without oxygen and nutrients. The compromised retina churns out vascular endothelial growth factor (VEGF), a protein that makes retinal blood vessels more leaky and stimulates new blood vessel growth. Fluid pooling in the macula - the retina’s central site for reading or driving acuity - is called macular edema and harms vision.

One treatment for diabetic macular edema is focal laser photocoagulation, which can reduce leakage over months or years, but it not effective in all patients. Johns Hopkins studies show that intraocular injections of ranibizumab or bevacizumab (antibodies against VEGF) might benefit patients with diabetic macular edema, although these agents are not currently approved by the FDA for this use. Additional trials to test higher doses of ranibizumab in patients with diabetic macular edema begin in early 2010.

Injections of steroids into the eye can also reduce leakiness of retinal vessels. Benefits vary, and new ways of delivering steroids might increase their benefit.

• As damage to the retina causes more vessels to shut down, levels of VEGF increase to the point that new blood vessel growth occurs. Unfortunately, these new blood vessels are fragile and often bleed. Floaters and streaks that blur vision provide a warning sign of this advanced form of diabetic retinopathy, so it is important to institute scatter laser photocoagulation, a nonpainful procedure. If the condition is left untreated, scar tissue can form, increasing the risk of a detached retina and blindness unless corrected by surgery. Even at this advanced stage of the disease, some vision can often be salvaged unless surgery is delayed.