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.
Earlier, 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
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