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CONTACT: NEI Information Office
October 30, 1989
New findings from a nationwide clinical trial supported by the National Eye Institute (NEI) provide further evidence that laser treatment is highly effective in preventing visual loss from diabetic eye disease. Of the estimated 11 million Americans who have diabetes, about 10 percent have vision-threatening diabetic retinopathy, one of the leading causes of blindness among young adults. It is the advanced stage of diabetic retinopathy with hemorrhage that, if left untreated, leads to severe visual loss.
Long before a person notices blurring of vision from diabetic retinopathy, an eye examination can reveal abnormalities in the retina, such as the growth of abnormal blood vessels, hemorrhages (bleeding), closure of blood vessels, and leakage of fluid. This leakage may cause macular edema (swelling of the macula). The macula is the part of the retina that provides sharp, central vision.
The Early Treatment Diabetic Retinopathy Study (ETDRS), was initiated in 1979 by the NEI, part of the National Institutes of Health. It was based on results from the Diabetic Retinopathy Study (DRS), an earlier clinical trial that showed laser treatment is effective in reducing the risk of severe visual loss from the advanced stage of diabetic retinopathy. The ETDRS posed three unresolved questions: Is laser treatment effective for diabetic macular edema? When in the course of the disease is the best time to begin laser treatment for diabetic retinopathy? Does aspirin treatment alter the progression of diabetic retinopathy?
This controlled, multicenter clinical trial involved 3,711 patients at 22 medical centers nationwide. To find answers to the three ETDRS questions, all patients were assigned to either aspirin treatment or a placebo, and to two types of laser treatment for diabetic retinopathy--focal and scatter. In focal treatment, the laser beam is aimed at and seals the leaky retinal blood vessels that cause macular edema. In scatter treatment, the laser beam is used to produce many tiny burns scattered throughout the retina, sparing the macula. This slows the growth of new blood vessels and the development of hemorrhage and scar tissue.
To evaluate the effect of laser treatment, one eye of each patient was randomly assigned to receive immediate treatment. The other eye initially was not treated, but was carefully followed and evaluated every four months and received laser treatment if the eye progressed to the advanced stage of retinopathy, sometimes called high-risk retinopathy, a stage of disease likely to lead to severe visual loss if untreated.
Eyes selected for immediate treatment received one of four different combinations of focal and scatter treatment. By varying the amount of scatter treatment given and the time of initiation of focal treatment for macular edema, the study investigators hoped to find the best possible early treatment strategy.
Focal treatment for macular edema proved so helpful in reducing the risk of visual loss that in 1985 ETDRS scientists changed the treatment plan. After that, both eyes of every patient in the study were eligible to receive focal treatment if vision was threatened by macular edema. The final study conclusions support these original findings.
Study conclusions also revealed that scatter treatment reduces the risk of severe visual loss whether given early or deferred until the development of high-risk retinopathy. Provided careful followup can be maintained, study investigators concluded that it is safe to defer scatter treatment until retinopathy approaches or reaches the high-risk stage. The study found that the rates of severe visual loss were low for all ETDRS patients.
The Study also investigated the effects of aspirin on retinopathy. According to anecdotal information, the incidence of severe retinopathy seemed lower than expected in diabetic patients taking aspirin for arthritis. Because aspirin is known to slow blood platelet clumping, ETDRS scientists decided to test whether aspirin could change a person's blood chemistry in ways that affect the development of retinopathy. They concluded that two aspirins a day (650 mg) does not alter the progression of diabetic retinopathy, and there is no reason for people with diabetes to avoid taking aspirin when it is needed for treatment of other problems.
The ETDRS recommendations can be used by people with diabetes and their physicians to determine the best approach for management of diabetic retinopathy and macular edema. Regular, comprehensive eye examinations through dilated pupils will enable early detection and appropriate treatment so that people with diabetes can maintain good vision.
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