Amblyopia, also known as lazy eye, is a vision development disorder in which an eye fails to achieve normal visual acuity, even with prescription eyeglasses or contact lenses.
Amblyopia begins during infancy and early childhood. In most cases, only one eye is affected. But in some cases, reduced visual acuity can occur in both eyes. Particularly if lazy eye is detected early in life and promptly treated, reduced vision can be avoided. But if left untreated, lazy eye can cause severe visual disability in the affected eye, including legal blindness. It’s estimated that about 2 to 3 percent of the U.S. population has some degree of amblyopia. Because amblyopia typically is a problem of infant vision development, symptoms of the condition can be difficult to discern. However, a common cause of amblyopia is strabismus. So if you notice your baby or young child has crossed eyes or some other apparent eye misalignment, schedule an appointment for a children’s eye exam immediately.
Another clue that your child may have amblyopia is if he or she cries or fusses when you cover one eye. You can try this simple screening test at home by simply covering and uncovering your child’s eyes (one eye at a time) when he or she is performing a visual task, such as watching television. If your child is not bothered when one eye is covered, but objects when the other eye is, this may suggest that the eye you have covered is the “good” eye, and that the uncovered eye is amblyopic, causing blurred vision.
But a simple screening test is no substitute for a comprehensive eye exam. Have your child’s eyes examined as recommended to make sure he or she has normal vision in both eyes and that the eyes function together properly as a team.
There are three types of amblyopia, based on the underlying cause:
- Strabismic amblyopia. Strabismus is the most common cause of amblyopia. To avoid double vision caused by poorly aligned eyes, the brain ignores the visual input from the misaligned eye, leading to amblyopia in that eye (the “lazy eye”). This type of amblyopia is called strabismic amblyopia.
- Refractive amblyopia. Sometimes, amblyopia is caused by unequal refractive errors in the two eyes, despite perfect eye alignment. For example, one eye may have significant uncorrected nearsightedness or farsightedness, while the other eye does not. Or one eye may have significant astigmatism and the other eye does not. In such cases, the brain relies on the eye that has less uncorrected refractive error and “tunes out” the blurred vision from the other eye, causing amblyopia in that eye from disuse. This type of amblyopia is called refractive amblyopia.
- Deprivation amblyopia. This is lazy eye caused by something that obstructs light from entering and being focused in a baby’s eye, such as a congenital cataract. Prompt treatment of congenital cataracts is necessary to allow normal visual development to occur.
In some cases of refractive amblyopia, normal vision can be achieved simply by fully correcting the refractive errors in both eyes with glasses or contact lenses. Usually, however, at least some patching of the “good” eye is needed to force the brain to pay attention to the visual input from the amblyopic eye and enable normal vision development to occur in that eye.
Treatment of strabismic amblyopia often involves strabismus surgery to straighten the eyes, followed by eye patching and often some form of vision therapy to help both eyes work together equally as a team. Patching may be required for several hours each day or even all day long and may continue for weeks or months.