Overview of Amblyopia
Amblyopia, also known as "lazy eye," is a condition characterized by diminished vision in one eye. It is not correctable by eyeglasses or contact lenses and is not usually triggered by an eye disease. Instead, amblyopia can develop when:
- the extraocular muscles fail to align the eyes properly and the part of the brain that controls vision "favors" one eye over the other;
- an eye with a significant refractive error in one eye goes uncorrected for a period of time; or
- there is a large difference in the refractive power, and one eye is favored.
Babies are born with poor eyesight that normally improves as they grow. In amblyopia, one eye becomes stronger. If the weaker eye is untreated, eyesight will progressively worsen.
Incidence & Prevalence of Amblyopia
Amblyopia is the most common cause of visual impairment restricted to one eye in children and young to middle-aged adults. About 5 percent of children in the United States have amblyopia.
Types of Amblyopia
The two most common types of amblyopia are strabismic and anisometropic. In strabismic amblyopia, strabismus is present and the eyes are not aligned properly resulting in one eye being used less than the other. The nonpreferred eye is not adequately stimulated and the visual brain cells do not develop normally.
With anisometropic amblyopia, the eyes have different refractive powers. For example, one eye may be nearsighted and the other farsighted. It may be difficult for the brain to balance the difference and it favors the stronger eye.
Risk Factors for Amblyopia
Anything that interferes with equal development of vision in both eyes between birth and about 6 years can result in amblyopia. Strabismus and anisomtreopia are the most common causes of amblyopia. Other risk factors include congenital cataracts, something that blocks the cornea or lens, and a droopy eyelid that obstructs the field of vision in one eye.
Signs and Symptoms of Amblyopia
Amblyopia may not produce symptoms that are obvious to a parent or the affected child. Amblyopia caused by an undetected refractive error may go unnoticed for years, due to the fact that one of the eyes is functioning normally. As a result, many children remain unaware of vision problems, especially before they begin school. The condition is often diagnosed during the first eye examination at a later age, when improvement in vision to its fullest potential may no longer be possible.
Sometimes, though, a child may squint or close one eye, which indicates a visual problem. A child old enough to verbalize may complain of headaches or eyestrain. In strabismic amblyopia, the crossed eye is an obvious sign.