Many eye doctors believed until recently that if a child's vision was impaired because of a "lazy eye," the condition could not be corrected past the age of six or seven years. However, a study funded by the National Eye Institute, part of the National Institutes of Health, has found that amblyopia or "lazy eye" treatment can be effective in children age seven through 17. In fact, many of the 517 children studied at 49 eye centers showed improvement in their vision.
"Age alone should not determine whether or not to treat," said Michael Repka, M.D., a pediatric ophthalmologist at the Johns Hopkins Children's Center and a co-author of the study. Even teenagers benefit from treatment, said Repka.
Amblyopia is a common cause of vision loss in as many as 3% of children in the US. During infancy or childhood, the vision loss occurs when the brain favors one eye over the other. The other healthy eye does not receive brain input, limiting visual development. The most common causes of 'lazy eye" are nearsightedness, farsightedness, or a crossed or wandering eye (strabismus).
The reason vision in the amblyopic eye improves is due to the brain's plasticity, says Susan Cotter, O.D., a pediatric optometrist at the Southern California College of Optometry and co-author of the treatment study. Neuroplasticity means the brain can change with learning. By forcing the unused eye to work, the brain will process the sensory information and adapt. As a result, vision improves.
Children in the study were divided into two groups, randomly selected. One group wore only prescription classes. The other group either wore glasses and an eye patch or glasses, an eye patch and eye drops. The latter group was also instructed to read, draw, or do other close-up activities as well since "near-vision activities are visually stimulating," says Cotter.
The patch, eye drops and close-up work forced the test subjects to use their amblyopic eyes. Children wore the patch for two to six hours per day. Children 12 years and less also used eye drops.
However, "eye drops blur the eye all day which is why the teenagers wore only patches, which could be removed while driving," says Cotter.
If children in the study could read two more lines on the eye chart with the amblyopic eye, the treatment was considered successful.
According to the National Eye Institute, 53% of children in the study ages 7 through 12 who wore glasses and a patch for 2-6 hours per day, and did near-vision activities could read two or more lines on the eye chart after 24 weeks. But only 25% in this age group could do the same. Twenty-five per cent of children ages 13 through 17 who wore eye glasses and a patch had improved vision whereas 23% who wore only glasses improved. Of those children in this age group who had been previously treated for amblyopia, 47% who wore glasses and a patch and did close-up work had improved vision. On the other hand, only 20 % improved who were treated with only glasses.
"This study shows how important it is to screen children of all ages for amblyopia," said study co-chairman Richard W. Hertle, M.D., Children's Hospital of Pittsburgh.
If children also have strabismus and will undergo surgery to correct the eye muscle imbalance, they should be treated first for amblyopia, says Cotter. "Surgery doesn't help amblyopia. If the child has surgery and amblyopia still exists, one eye with 20/100 vision, for instance, will be blurry; consequently it will be difficult or impossible for the brain to fuse the two images together into one," says Cotter.
Atropine eye drops may serve to improve compliance because the child doesn't require monitoring. Adhesive patches are also used to increase compliance in young children as it is difficult for them to peek. "Children can't be monitored all day," says Cotter.
Although the adhesive patch is hypoallergenic, some children with sensitive skin experience irritation when the patch is removed. So some doctors allow their patients to switch to cloth patches. Cloth patches with side shields still block vision in the affected eye.
The number of hours that the children wore their patch was through self report. "This is a real world, treatment effectiveness study," says Cotter. "I do the same clinically."
A new study is planned to learn about the effects of near-vision activities on amblyopia.
Article reviewed by
Susan Cotter, O.D.
Southern California College of Optometry
Diana Clarke is a teacher and health educator. Her articles have appeared in newspapers and magazines, such as the San Jose Mercury News and the World of English.