Strabismus is a vision problem in which both eyes do not look at the same point at the same time. It usually develops during childhood and is sometimes called "crossed-eyes," "walleye," or "squint."

Normally, the muscles surrounding each eye work together to move both eyes in the same direction at the same time. Strabismus occurs when the eye muscles do not work properly to control eye movement. The cause is often not known. Possible causes include farsightedness, head injury, and muscle and nerve disorders that weaken or damage the muscles that control eye movement.

Without treatment, strabismus can cause permanent vision problems. Not using one eye can also lead to poor vision in that eye (called lazy eye or amblyopia).