New evidence, based on a 2006 laboratory study and a novel clinical trial by researchers in the U.S. and China, has suggested a simple and effective therapy for amblyopia, or "lazy eye."
The treatment discovered by a team of researchers led by Zhong-Lin Lu, a neuroscientist at the University of Southern California, was found to be effective on 20-year-old subjects.
AdvertisementEarlier, amblyopia was considered mostly irreversible after 8 years of age. In fact, a large number of amblyopes, especially in developing countries, are diagnosed very late so that they can get conventional treatment with an eye patch.
Lu said that patients hoping to get treatment would need to wait for eye doctors to adopt the non-surgical procedure in their clinics.
"I would be very happy to have some clinicians use the procedure to treat patients. It will take some time for them to be convinced. We also have a lot of research to do to make the procedure better," he said.
He added that in a pilot clinical trial at a Beijing hospital in 2007, 28 out of 30 patients displayed dramatic gains after a 10-day course of treatment.
"After training, they start to use both eyes. Some people got to 20/20. By clinical standards, they're completely normal. They're not amblyopes anymore," he said.
The gains averaged two to three lines on a standard eye chart. Previous studies by Lu's group found that the improvement is long-lasting, with 90 percent of vision gain retained after at least a year.
"This is a brilliant study that addresses a very important issue. The results have important implications for the treatment of amblyopia and possibly other clinical conditions," said Dennis Levi, dean of optometry at the University of California, Berkeley.
It was shown that the advantage of the training protocol, involving a very simple visual task, goes far beyond the task itself. According to Lu, amblyopes trained on just one task improved their overall vision and this improvement was much greater for amblyopes than for normal subjects.
"For amblyopes, the neural wiring is messed up. Any improvement you can give to the system may have much larger impacts on the system than for normals," he said.
The results of the study also have major theoretical implications. Amblyopia was considered incurable due to a long held notion of "critical period": that the visual system loses its plasticity and ability to change after a certain age.
"This is a challenge to the idea of critical period. The system is much more plastic than the idea of critical period implies. The fact that we can drastically change people's vision at age 20 says something," said Lu.
However, he added that a critical period still exists for certain functions, but it might be more limited than previously thought.
"Amblyopia is a great model to re-examine the notion of critical period," he said.
The first study by Lu's group on the plasticity of amblyopic brains was conducted in 2006 and attracted wide media attention and Lu was bombarded with hundreds of emails from adult amblyopes who had assumed they were beyond help.
The results from this study are published in PNAS Early Edition.
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