Definition of Strabismus:

Strabismus is a disorder in which the two eyes do not line up in the same direction, and therefore do not look at the same object at the same time. The condition is more commonly known as "crossed eyes."

Causes, incidence, and risk factors:

Six different muscles surround the eyes and work "as a team" so that both eyes can focus on the same object.

In someone with strabismus, these muscles do not work together. As a result, one eye looks at one object, while the other eye turns in a different direction and is focused on another object.

When this occurs, two different images are sent to the brain -- one from each eye. This confuses the brain, and the brain may learn to ignore the image from the weaker eye.

If the strabismus is not treated, the eye that the brain ignores will never see well. This loss of vision is called amblyopia. Another name for amblyopia is "lazy eye." Sometimes amblyopia is present first, and it causes strabismus.

In most children with strabismus, the cause is unknown. In more than half of these cases, the problem is present at or shortly after birth (congenital strabismus).

Most of the time, the problem has to do with muscle control, and not with muscle strength.

Less often, problems with one of the nerves or muscles, or Graves' disease restriction may cause strabismus.

Other disorders associated with strabismus include:

• Brain and nerve disorders, such as traumatic brain injury, stroke, cerebral palsy, or Guillain-Barre syndrome
• Diabetes (causes a condition known as acquired paralytic strabismus)
• Damage to the retina in children who are born premature
• Hemangioma near the eye during infancy
• Injuries to the eye
• Tumor in the brain or eye
• Vision loss from any eye disease or injury

A family history of strabismus is a risk factor. Farsightedness may be a contributing factor, especially in children. Any other disease that causes vision loss may also cause strabismus.