Even after successful treatment for "lazy eye," people may still have certain vision problems in day-to-day life, a small study suggests.
The study, of 26 people with a history of lazy eye, found that even if their vision had returned to normal or near-normal after treatment, they still had more difficulty perceiving "real-world" images than people with healthy eyes.
They could accurately read letters on a chart - but they had fewer correct answers on a test that asked them to look at an everyday scene, like sculptures in front of a building, and then find the identical scene among a group of images shown next to the original.
The findings, reported in the Archives of Ophthalmology, suggest that even when treatment helps people with lazy eye do better on eye-chart tests in the doctor's office, their real-world vision may remain less than clear.
People with lazy eye, known medically as amblyopia, have weaker vision in one eye due to a problem in how the eyes and brain work together.
About 2 to 3 percent of children worldwide have lazy eye. It is sometimes caused by strabismus, where the eyes either "cross" or turn outward, affecting normal visual development. In other cases, lazy eye develops when a child is significantly more nearsighted or farsighted in one eye than the other.
Doctors treat the condition by forcing the weaker eye to work more -- by putting a patch over the stronger eye or using a special type of eye drops to temporarily blur vision in the stronger eye.
But while treatment can improve a child's visual acuity -- the part of vision that's measured during an eye-chart test -- that doesn't mean it rids them of all their visual difficulties.
"The significance of testing 'real-world' perception is that it gives us a better idea as to what people with amblyopia see in everyday life, rather than how well they see the eye chart," explained Dr. Agnes Wong, of the Hospital for Sick Children and the University of Toronto in Canada.
For their study, Wong's team recruited 26 children and adults with a history of lazy eye and 39 people with normal vision. The participants took a test in which they viewed images of everyday scenes; each image was shown along with a group of images that were all close to the original -- but only one was identical.
When the test-takers looked at the images with both eyes, those with healthy vision got the answer right 68 percent of the time, compared with 58 percent in the lazy eye group.
Eight of the people who'd had lazy eye had a best-corrected eye chart score of 20/25 or better -- what the researchers considered successful treatment. Another 12 had achieved vision of 20/40 or better, which is the minimum needed for a driver's license in the U.S.
Wong's team found that study participants who'd had their lazy eye successfully treated gave correct answers 64 percent of the time - more than the 59 percent for the rest of the lazy eye group, but still less than the 67 percent correct response rate in the group with normal vision.
According to Wong, a plausible explanation for these differences is that in children with lazy eye, the "visual brain" does not develop normally, and that has lasting effects.
"We believe that even if their visual acuity had been successfully treated, people with amblyopia may continue to have deficits in higher level processing of visual information because the 'damages' have been done early in life," Wong told Reuters Health in an email.
"Higher level" processing includes things like the brain's ability to perceive form and motion, according to Wong. Some past studies have found that people with lazy eye tend to have more difficulty with hand-eye coordination and motor skills than other people do.
Wong noted that people with lazy eye -- including those who eventually mastered the eye chart tests -- often have limits on their job choices and may have a generally poorer quality of life because of ongoing vision problems.
"This is why doing research is so important," she said. The goal is "to understand the brain mechanism that causes (lazy eye) and to find a cure for it."