Q: What is it?
A: Strabismus is a visual defect in which the eyes are misaligned and point in different directions. We've become accustomed to referring to this condition as crossed eyes, but actually strabismus refers to any situation where the eyes are not pointed in the same direction. This occurs when the muscles that control eye position and movement do not work together properly. When that happens, one eye might be pointing in or out, or up or down, while the other eye is looking straight ahead. If the eyes are looking in two different directions, they will each see a different image. Then, not only is it difficult or impossible to judge depth, but the brain learns to favor one image over another. Crossed eyes, if not corrected early, can lead to a condition known as lazy eye, or what eye specialists call amblyopia. This occurs when the same eye always turns away and becomes weaker or lazy. If not treated, that eye will eventually become useless.
The two most common types of strabismus are esotropia and exotropia. Esotropia describes an inward turning eye. Exotropia describes an outward turning eye. Children as well as adults can have strabismus. Strabismus affects about 4% of the children's population. Strabismus can be hereditary. However, many people have strabismus with no trace of the problem in any other family member.
Q: What are the signs or symptoms?
A: The primary symptom of strabismus is an eye that is not straight. Sometimes a child will squint one eye in bright sunlight or tilt their head in a specific direction in order to use their eyes together, signs of faulty depth perception may also be noticed. Adults who acquire strabismus will usually have double vision. It's difficult for a parent to determine whether or not an infant's eyes are working together properly. At birth, and for the first few months of life, a baby's eyes sometimes seem to be moving independently of one another. Yet the eyes are gaining in strength and coordination, and usually by six months of age they are functioning as they should.
Q: What causes it?
A: The exact cause of eye misalignment that leads to strabismus is not fully understood. To line up and focus both eyes on a single object, all eye muscles of each eye must be balanced and working together with the corresponding muscles of the opposite eye. The brain controls the eye muscles, which explains why children with disorders that affect the brain, such as cerebral palsy, Down's syndrome, hydrocephalus and brain tumors, often have strabismus. A cataract or eye injury that affects vision can also cause strabismus.
Q: How is it detected?
A: Children should have a thorough medical examination during infancy and preschool years to detect potential eye problems. This is particularly important if a relative has strabismus.
Q: How is it treated?
A: Treatment goals for strabismus are to preserve vision, and to straighten the eyes, and to restore binocular vision. The simplest treatment is corrective lenses. Eye drops may be prescribed. In some cases, eye exercises are helpful. Eye patches, used in combination with glasses or surgery are beneficial to some patients. Surgery not only permits the eyes to develop normally, but it also improves one's appearance. Early surgery is recommended to correct strabismus because younger infants can develop normal sight and binocular vision once the eyes are straightened. As a child gets older, the chance of developing normal sight and binocular vision decreases, although side vision may improve. Correction of strabismus after age 6 will improve appearance, but cannot provide a second chance to learn binocularity.