The retinas of the eyes convert light into chemical signals that travel along the optic nerve and are interpreted by the brain, resulting in vision. Disturbances in vision can occur at the level of the eyes, the optic nerve, or the brain area that processes visual information. In the condition known as amblyopia, sometimes called "lazy eye," an abnormal interaction between one eye and the brain diminishes vision.
Prevalence
According to the National Eye Institute, amblyopia is the most common cause of impaired vision in childhood, affecting 2 to 3 percent of children. Amblyopia is also the most common reason for visual impairment in one eye in children and young and middle-aged adults.
Symptoms
In amblyopia, the eyes can appear normal, or there can be some strabismus---muscle weakness that allows the affected eye to wander, relative to the other eye. The affected eye can wander inward, which is called esotropia or crossed eye; or outward, which is called exotropia or wall eye. Vision in the affected eye is blurry, and depth perception, which requires coordinated information from two eyes, is poor. In many cases, the other eye compensates so well that there are no symptoms until the patient undergoes a routine vision test.
Causes
Amblyopia tends to run in families, which suggests that there is a genetic contribution. Children with developmental delays or children born prematurely are more likely to be affected. Sometimes a problem with the structure of the eye, such as a cataract; an abnormal shape or position of the retina; an abnormal shape of the eye itself; or a noticeable difference in size between the eyes causes amblyopia. However, MayoClinic.com notes that the most common cause is strabismus, which prevents the eyes from tracking with each other. The brain learns to filter out the information from the wandering eye, causing the vision problems of amblyopia.
Complications
When detected and treated early, amblyopia is usually corrected with no permanent damage. However, if left untreated, amblyopia can lead to permanent loss of vision in the affected eye. As MayoClinic.com points out, sometimes strabismus can be a sign of an eye tumor, as well as an indication of amblyopia.
Treatment
Early childhood is the optimal time to treat amblyopia, because the visual system forges its lifelong connections to the brain in the first six to nine years of life, according to the National Eye Institute. An ophthalmalogist might prescribe an eye patch to wear over the stronger eye for two or more hours per day, to force the weaker eye to work harder and foster the formation of proper eye-brain connections. An alternative therapy involves using atropine eye drops once or twice per week to blur vision in the stronger eye, again promoting use of the weaker eye.
