ew 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.
