Strabismus
Strabismus is a condition in which the eyes cross or do not work togetber normally, which may lead to permanent loss of vision in one eye.
What Is Strabismus?
When people cross their eyes, the world suddenly doubles. Images, like the words on this page, become blurred, and it appears as if there are two of each. When the eyes function correctly, they work together to focus images and to allow the brain to develop a three-dimensional view of the world. But when the eyes cannot work together, as when people cross their eyes, the brain sees double. The result is double vision.
Fortunately, both eyes work together for most people. But some people have an eye disorder that causes the eyes to fail to line up properly, resulting in blurred or double vision. This condition is called strabismus (stra-BIZ-mus), which comes from a Greek word that means squinting. Often in strabismus, one eye may remain straight and the other eye may turn in, which may look to others as if the person is crossing one eye.
Why Do People Have Strabismus?
Strabismus usually develops during infancy or early childhood. In most cases, there is no known cause, although sometimes several members of the same family have the disorder, which may mean that in some cases strabismus is inherited, like eye color is. Other possible causes include the following:
* Farsightedness, causing focus difficulties
* Damage to one eye or to the part of the brain that controls the muscles involved in eye movement
* Other disorders that affect the brain, including Down syndrome, cerebral palsy, and hydrocephalus
* Less commonly, vision is blocked by a tumor or cataracts that causes cloudiness in the normally clear lens of the eye. Strabismus affects about 3 to 5 percent of children in the United States. It occurs in boys and girls equally. Fortunately, if it is diagnosed and treated early, there is a good chance of saving or improving vision in the affected eye.
Some adults have strabismus, perhaps because they were not treated for it as a child or because the treatment was not effective. Other adults may develop strabismus when a disorder such as stroke* causes the eyes to cross or not work together normally.
How Do Six Muscles in Each Eye Work as One?
The eyes and the nerves that connect them to the brain work like the two lenses of binoculars. They merge the image seen by each eye into one image. Six muscles are attached to each eye, and they control how the eyeball moves left and right or up and down. To make it possible for the brain to develop a single three-dimensional image, the muscles must work together to focus, just as the two lenses of binoculars must be aligned to focus together.
People with strabismus have trouble with one or more of the muscles in an eye. Instead of working together, one eye is out of alignment. Sometimes strabismus seems to come and go, depending on how tired the eyes are, and sometimes the eyes remain out of correct position. There are different forms of strabismus:
* When one eye points inward toward the nose, which makes the person look cross-eyed, the condition is esotropia (es-o-TRO-pe-a).
* When one eye points away from the nose, as if looking to the outside, the condition is exotropia (ek-so-TRO-pe-a) or walleye.
* When the brain turns off the vision in the turned eye in favor of the vision in the straight eye, the condition is called strabismic amblyopia (stra-BIZ-mik am-blee-O-pee-a) or lazy cye. Amblyopia does not mean that the eye is lazy. Instead, the brain turns off the image coming from the optic nerve in that eye so the person sees only one clear image of the world instead of having blurred or double vision.
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