A lazy eye is usually healthy: the brain is what stops listening
In amblyopia the weaker eye often looks perfectly normal. The problem sits behind it: during early childhood the brain learns to favour one eye and tunes out the other. Fixing the original cause does not restore sight straight away, because the visual system itself has developed around the imbalance.
Amblyopia is the most common reason for reduced vision in one eye among children and younger adults, and it begins by the age of five. Estimates suggest it affects between 1 and 5 percent of adults. It was first described in the 1600s, and its name joins Greek words for blunt and eye.
Anything that disrupts focusing early in life can cause it. The most common type is strabismic: the eyes point in different directions, and a young, highly adaptable brain avoids double vision by suppressing one image. Adults who develop a squint later simply see double, because their brains are no longer flexible enough to ignore an eye. Refractive amblyopia arises when one eye is much more short- or long-sighted than the other and sends a blurrier picture; it tends to be milder and is easily missed because nothing looks wrong. Deprivation amblyopia, caused by something blocking light such as a congenital cataract or a drooping eyelid, accounts for under 3 percent of cases.
Because the stronger eye sees well, many people with a mild form never notice until they are tested. What they lose is mostly binocular: stereo depth perception is poor, and hidden three-dimensional pictures such as autostereograms are hard to see, though cues like size, perspective and motion still give a sense of depth. People with the strabismic type may also read more slowly, making extra eye jumps along each line even with their good eye.
Screening around ages four to five is recommended because early detection improves results. Glasses alone are sometimes enough; otherwise the stronger eye is covered with a patch or blurred with atropine drops, which also spares children the teasing a patch can bring. Treatment in adulthood works far less well, and even successful treatment rarely makes the weaker eye fully normal. The condition can rule people out of jobs such as pilot or police officer.
Source: Amblyopia
