Vision improved temporarily, Canadian researchers report
FRIDAY, July 18 (HealthDay News) -- Correcting lazy eye in adults is supposed to be impossible, but researchers report they have been able to do that -- at least partially and temporarily -- by beaming magnetic pulses into the brain.
Someone with lazy eye -- ophthalmologists call it amblyopia -- has poor vision because one eye is weaker than the other. Early treatment often has a child wearing a patch over the strong eye to strengthen the weaker one, but the problem has been thought to be untreatable in adulthood. Most of the estimated 6 million Americans with amblyopia are adults.
"We know now that visual loss is caused by poor processing in the cortex," said Benjamin Thompson, a postdoctoral fellow in the ophthalmology department at McGill University in Canada, and a member of the group reporting on the new method in the July 22 issue of Current Biology. "Treatment usually addresses the problem with the eye, not with the cortex."
The study was prompted in part by research at a number of institutions showing that changes can occur in the adult brain, which until recently was thought to be impossible.
The cortex is a vital part of the brain, involved in vision among other functions. Work by other researchers has shown that transcranial magnetic stimulation, in which a rapid train of magnetic impulses is delivered to the brain through a hand-held coil placed on the scalp, has been effective in stroke rehabilitation and is being tested against depression.
When it was tried on nine adults with amblyopia, 15 minutes of magnetic stimulation improved the sensitivity of the weaker eye temporarily, Thompson said. In visual tests, they were able to see finer details than before the treatment.
"We were surprised by how well it worked," he said. "Vision in the amblyopic eye improved for at least 20 minutes after transcranial magnetic stimulation."
It was admittedly a small trial, but "one of the issues we were addressing was whether amblyopia could be treated in adults," Thompson said. "The adult brain doesn't have the same capacity for change as in children."
There are two ways to exploit the finding, and the McGill group plans to try both of them, Thomson said. One route is to use multiple bouts of transcranial stimulation.
"We've only tried a single dose so far in our study," he said. "Now, we can look at the effect of repeated doses. In depression, it seems they can have an effect."
The other possibility is to use magnetic stimulation to prime the brain for a rehabilitation program, a training regimen in which adults are asked to perform a series of visual tasks. Recent studies have indicated that such a perceptual training program can improve vision in amblyopic eyes.
"We will also have a parallel project, a training regime with stimuli to both eyes, higher-contrast stimuli to the amblyopic eye," Thompson said. "We hope that repeated exposure will bring improvement."
The report is one of several indicating that the adult brain has more capacity for change than had been thought, said Dr. Robert Cykiert, a clinical associate professor of ophthalmology at New York University.
Lazy eye occurs because the proper connections between the eye and the cortex do not form early in life, Cykiert explained. "We thought that if the connections do not form by age 10 or so, it is too late."
The McGill study indicates otherwise, he noted. "The study has very preliminary results, but obviously this may lead to other related or similar treatments that may have a more lasting effect," Cykiert said. "What we might be able to do is to allow people with lazy eye to have treatments that stimulate that part of the brain."
Amblyopia and its current treatments are described by the National Eye Institute.
SOURCES: Benjamin Thompson, Ph.D., postdoctoral fellow, ophthalmology department, McGill University, Montreal; Robert Cykiert, clinical associate professor, ophthalmology, New York University, New York City; July 22, 2008, Current Biology
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