How many times have you seen a young child with a patch over one eye or wearing glasses with one lens blocked and wondered why? Chances are that child has something called amblyopia (sometimes called "lazy eye"), where one eye is not being used by the brain because it doesn't see as well.

After looking at more than 10 years of data, researchers now say children as young as a year old can be reliably screened for amblyopia; by using a camera that takes pictures of the eye, symptoms of the condition can be detected long before it becomes apparent, according to a study published Monday in the journal Pediatrics.

The goal is to identify children with this problem as early as possible, says lead study author Dr. Susannah Longmuir, "so we can start treatment before they have a problem or treat it before it gets worse."

She says very young children can already be developing amblyopia, but they do not know they have a vision problem because it's all they know - and they appear to parents to have normal vision. But as they get older, the problem gets worse.

One eye could be out of focus, or the eyes aren't straight and the brain doesn't want to see double, so it turns off the bad eye, says Dr. Daniel Neely, chairman of the vision screening committee for the American Association for Pediatric Ophthalmology and Strabismus (AAPOS), who was not involved in the research.

The brain then gets used to not using the eye, he says. But the brain can be re-taught how to use the eye that's just not doing enough -- if caught early. That's where the patches, glasses or eye drops come in. By covering the good eye up or putting eye drops in to make the vision in the good eye blurry, the brain is forced to used the other eye.

"We know that after age 5, the effectiveness of the treatment is diminished," Neely adds. "The problem is most vision screenings happen when kids go to school," he says - close to when the window of correction closes.

"Current U.S. Preventive Services Task Force (USPSTF) guidelines, issued in January 2011, only recommend testing children for this eye condition between the ages of 3 and 5, citing insufficient evidence to recommend testing younger children.

The study

Researchers at the University of Iowa designed a study to help the USPSTF by providing the necessary evidence to include toddlers in their recommendations, says Longmuir.