Waking up that lazy eye.

In amblyopia--"lazy eye"--the brain prefers images from one eye over the other. Most doctors treat the condition in children by patching the good eye for part of each day, but assume that the practice doesn't work past age 10. Some doctors give up on patching at age 7.

A U.S.-Canadian study now finds that children up to age 17 can make significant gains in vision by wearing a patch.

Researchers identified 507 children with amblyopia and randomly assigned half of them to wear a patch from 2 to 6 hours a day for 24 weeks. If needed, the kids also received prescriptions for eyeglasses. All the children were between 7 and 17 years old.

Children ages 7 to 12 who wore patches were four times as likely as those who didn't to improve their vision in the weak eye by two rows on the standard 11-line eye chart that doctors use to assess eyesight, the scientists report in the April Archives of Ophthalmology. Kids with amblyopia usually have a lazy eye that reads down to only the middle of the chart. People with normal vision see down to about the 10th row.

Children 13 to 17 also gained some visual clarity by wearing a patch, but only if they hadn't received such therapy earlier in their lives. Their gains were smaller than those of 7-to-12-year-olds but still significant, says study coauthor Richard W. Hertle of the University of Pittsburgh.

Long-term follow-up might reveal whether the vision improvements are permanent, Hertle says.