USC Health Now

New data from a USC researcher show promise in the treatment of “lazy eye,” a condition previously considered mostly irreversible in adults.

March 17, 2008
by Carl Marziali

Ambylopia, or “lazy eye”, is a disorder is caused by poor transmission of images from the eye to the brain during early childhood, leading to abnormal brain development. Lazy eye is actually a misnomer because in many cases the structure of the eye is normal.

According to the National Eye Institute, ambylopia is the most common cause of visual impairment in childhood and affects approximately two to three out of every 100 children.

Now, new evidence from laboratory studies and a pilot clinical trial confirms the promise of a simple treatment for amblyopia, according to researchers from the United States and China. The group’s study appears online in PNAS Early Edition, the journal of the U.S. National Academy of Sciences.

The treatment—which involves a very simple visual task—was effective on 20-year-old subjects. Previously, amblyopia was considered mostly irreversible after age 8.

Trial Results

In a pilot clinical trial at a Beijing hospital in 2007, 28 out of 30 patients showed dramatic gains after a 10-day course of treatment, says Zhong-Lin Lu, Ph.D., holder of the William M. Keck Chair in Cognitive Neuroscience, professor of psychology and biomedical engineering at the USC College of Letters, Arts and Sciences, and lead investigator on the trial.

“After training, they start to use both eyes. Some people got to 20/20,” says Lu, who is also co-director of the Dana and David Dornsife Cognitive Neuroscience Imaging Center at USC. “By clinical standards, they’re completely normal. They’re not amblyopes anymore.”

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.

Patients seeking treatment will need to wait for eye doctors to adopt the non-surgical procedure in their clinics, said Lu.

“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,” he points out. “We also have a lot of research to do to make the procedure better.”

Amblyopia affects about 3 percent of the population and cannot be rectified with glasses. People with the disorder suffer a range of symptoms: poor vision in one eye, poor depth perception, difficulty seeing three-dimensional objects and poor motion sensitivity.

Many amblyopes, especially in developing countries, are diagnosed too late for conventional treatment with an eye patch.

“There’s no consensus on how early eye screening should begin, but exams starting at six months of age can’t hurt and could pick up serious problems early,” says Rohit Varma, M.D., M.P.H., and professor of ophthalmology and preventive medicine at the Keck School of Medicine of USC. “If vision problems aren’t treated within the first few years when the brain is forming connections, normal vision may never be achieved.”

Looking Ahead

The PNAS study shows that the benefit of the training protocol goes far beyond the task itself. Amblyopes trained on just one task improved their overall vision, Lu said. The improvement was much greater for amblyopes than for normal subjects, he added.

“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 normal people [without amblyopia],” Lu said.

The Lu group’s findings also have major theoretical implications. The assumption of incurability for amblyopia rested on the 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,” Lu said. “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.”

A critical period still exists for certain functions, Lu added, but it might be more limited than previously thought.

“Amblyopia is a great model to reexamine the notion of critical period,” Lu said.

The first study by Lu’s group on the plasticity of amblyopic brains was published in the journal Vision Research in 2006 and attracted wide media attention. Since then, Lu has received hundreds of e-mails from adult amblyopes who had assumed they were beyond help.

Lu is collecting patients’ names for possible future clinical trials. He can be contacted at zhonglin@usc.edu.