A federal expert panel backtracked on Monday on its 2004 recommendation to screen all kids younger than five years for poor vision, lazy eye and other eye conditions.

Healthy children between three and five years should still be tested at least once, according to the U.S. Preventive Services Task Force (USPSTF), but there isn't enough solid evidence to recommend screening of all younger toddlers.

"There are harms associated with all screening tests," said Dr. Ned Calonge, chair of the USPSTF and past president of the Colorado Board of Medical Examiners. "We don't have good evidence of the harms, but we do know that at least some of these tests can generate a lot of false positives."

A misdiagnosed child, for instance, could end up with a bothersome eye patch -- a common treatment for lazy eye, or amblyopia -- or corrective lenses for no good reason.

Lazy eye, in which the brain neglects the input from one eye due to improper visual development, affects between 2 and 4 percent of preschoolers. It is the leading cause of poor vision in children and can lead to permanent vision loss on one eye if left untreated.

But according to the USPSTF, screening young toddlers is hard because they tend not to cooperate well with the eye professional. And waiting a few years before screening seems to be just as effective.

The new recommendations only cover those children without signs of vision problems. They don't mean parents with kids younger than three years should avoid making an appointment with the eye doctor if they are concerned.

"You may want to discuss screening with your healthcare provider, understanding that the evidence is insufficient at this point," said Calonge, adding that some of the newer screening devices are expensive.

USPSTF's advice is based on a new review of the medical literature, published in the journal Pediatrics.

According to that review, there is only limited direct evidence that screening leads to improved vision, and there are no data on how it affects school performance, for instance.

Still, in kids between three and five, the task force found the benefits of screening would likely outweigh the harms.

Patching the good eye to allow sight in the lazy eye to develop, for instance, led to a small increase in visual acuity -- less than one line on an eye chart, on average -- over the short term.

That difference could be considerable for a kid, said Calonge, and in theory might translate into much greater benefits in the long run because lazy eye causes more and more vision loss if untreated.

On the other hand, patching the good eye or using eye drops led to only a small and reversible loss of visual acuity on that eye.

In a commentary in the same issue of the journal, the American Academy of Ophthalmologists and other groups representing eye professionals said they were "concerned" about the USPSTF's new move.

They said eye examination with an ophthalmoscope -- a device that looks like a small flashlight -- or newer technologies should be used regularly in infants to rule out serious eye diseases such as cataracts that might lead to lazy eye.

Calonge said he had not seen the commentary, but noted that "we deal in the realm of being able to say with moderate certainty that screening provides more benefits than harms."