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New findings from a nationwide clinical trial supported by theNational Eye Institute (NEI) provide further evidence that lasertreatment is highly effective in preventing visual loss from diabeticeye disease. Of the estimated 11 million Americans who have diabetes,about 10 percent have vision-threatening diabetic retinopathy, one ofthe leading causes of blindness among young adults. It is the advancedstage of diabetic retinopathy with hemorrhage that, if left untreated,leads to severe visual loss.
Long before a person notices blurring of vision from diabeticretinopathy, an eye examination can reveal abnormalities in theretina, such as the growth of abnormal blood vessels, hemorrhages(bleeding), closure of blood vessels, and leakage of fluid. Thisleakage may cause macular edema (swelling of the macula). The maculais the part of the retina that provides sharp, central vision.
The Early Treatment Diabetic Retinopathy Study (ETDRS), wasinitiated in 1979 by the NEI, part of the National Institutes ofHealth. It was based on results from the Diabetic Retinopathy Study(DRS), an earlier clinical trial that showed laser treatment iseffective in reducing the risk of severe visual loss from the advancedstage of diabetic retinopathy. The ETDRS posed three unresolvedquestions: Is laser treatment effective for diabetic macular edema?When in the course of the disease is the best time to begin lasertreatment for diabetic retinopathy? Does aspirin treatment alter theprogression of diabetic retinopathy?
This controlled, multicenter clinical trial involved 3,711 patientsat 22 medical centers nationwide. To find answers to the three ETDRSquestions, all patients were assigned to either aspirin treatment or aplacebo, and to two types of laser treatment for diabeticretinopathy–focal and scatter. In focal treatment, the laser beam isaimed at and seals the leaky retinal blood vessels that cause macularedema. In scatter treatment, the laser beam is used to produce manytiny burns scattered throughout the retina, sparing the macula. Thisslows the growth of new blood vessels and the development ofhemorrhage and scar tissue.
To evaluate the effect of laser treatment, one eye of each patientwas randomly assigned to receive immediate treatment. The other eyeinitially was not treated, but was carefully followed and evaluatedevery four months and received laser treatment if the eye progressedto the advanced stage of retinopathy, sometimes called high-riskretinopathy, a stage of disease likely to lead to severe visual lossif untreated.
Eyes selected for immediate treatment received one of four differentcombinations of focal and scatter treatment. By varying the amount ofscatter treatment given and the time of initiation of focal treatmentfor macular edema, the study investigators hoped to find the bestpossible early treatment strategy.
Focal treatment for macular edema proved so helpful in reducing therisk of visual loss that in 1985 ETDRS scientists changed thetreatment plan. After that, both eyes of every patient in the studywere eligible to receive focal treatment if vision was threatened bymacular edema. The final study conclusions support these originalfindings.
Study conclusions also revealed that scatter treatment reduces therisk of severe visual loss whether given early or deferred until thedevelopment of high-risk retinopathy. Provided careful followup can bemaintained, study investigators concluded that it is safe to deferscatter treatment until retinopathy approaches or reaches thehigh-risk stage. The study found that the rates of severe visual losswere low for all ETDRS patients.
The Study also investigated the effects of aspirin on retinopathy.According to anecdotal information, the incidence of severeretinopathy seemed lower than expected in diabetic patients takingaspirin for arthritis. Because aspirin is known to slow blood plateletclumping, ETDRS scientists decided to test whether aspirin couldchange a person’s blood chemistry in ways that affect the developmentof retinopathy. They concluded that two aspirins a day (650 mg) doesnot alter the progression of diabetic retinopathy, and there is noreason for people with diabetes to avoid taking aspirin when it isneeded for treatment of other problems.
The ETDRS recommendations can be used by people with diabetes andtheir physicians to determine the best approach for management ofdiabetic retinopathy and macular edema. Regular, comprehensive eyeexaminations through dilated pupils will enable early detection andappropriate treatment so that people with diabetes can maintain goodvision.
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- Kinyoun J, Barton F, Fisher M, Hubbard L, Aiello L, Ferris F 3rd. Detection of Macular Edema. Ophthalmoscopy Versus PhotographyEarly Treatment Diabetic Retinopathy Study Report Number 5. The ETDRS Research Group. Ophthalmology. 1989 Jun. PubMed