Encyclopedia - Strabismus (Cross-Eyes)

What makes strabismus occur?
What are the signs of strabismus?
How is strabismus detected and treated?

Strabismus is a functional defect where the eyes are misaligned and point in different directions. The brain’s ability to see three-dimensional objects depends on proper alignment of the eyes. When both eyes are properly aligned and aimed at the same target, the visual portion of the brain fuses the forms into a single image. When one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain. This causes loss of depth perception and binocular vision. The turned eye may be straight at times, and the misalignment may come and go. Strabismus occurs in about 4 percent of all children in the United States, equally in males and females, and is sometimes hereditary. The condition can also develop later in life.

There are two forms of strabismus, esotropia and exotropia. In esotropia, one eye deviates inward toward the nose, while in exotropia, one eye deviates outward away from the nose. Esotropia is the most common type of strabismus in infants, while exotropia often begins between the ages of 2 and 4.

In young children with any form of strabismus, the brain may learn to ignore the misaligned eye’s image and see only the image from the best-seeing eye. This is called amblyopia, or lazy eye, and results in a loss of depth perception. When an adult develops strabismus, double vision sometimes occurs because the brain has already been trained to receive images from both eyes and cannot ignore the image from the turned eye.

What makes strabismus occur?

The causes of strabismus are not fully understood. There are six muscles that control eye movement, four that move it up and down and two that move it side to side. All these muscles must be coordinated and working properly in order for the brain to see a single image. When one or more of these muscles doesn’t work properly, some form of strabismus may occur. Strabismus is more common in children with disorders that affect the brain such as cerebral palsy, Down syndrome, hydrocephalus, and brain tumors.

What are the signs of strabismus?

The earliest sign of strabismus is usually a noticeable deviation of one eye. This symptom may at first be intermittent, occurring when a child is daydreaming, not feeling well, or tired. The deviation may also be more noticeable when the child looks at something in the distance. Frequent rubbing of the eyes is also common with strabismus. In bright light, children may squint or tilt their heads in order to use both eyes together. Few children ever complain about double vision, although they may close one eye to compensate for the problem.

The eyes of infants and small children can sometimes seem to be crossed when they have a wide, flat nose and a fold of skin at the inner eyelid. Called false strabismus, it usually disappears as the child grows. True strabismus will not be outgrown. An eye doctor can tell the difference between true and false strabismus.

How is strabismus detected and treated?

To diagnose strabismus, an eye doctor will perform a comprehensive eye examination including an ocular motility (eye movement) evaluation and an evaluation of the internal ocular structures. The most reliable treatment for strabismus is usually eye muscle surgery, but this is often preceded by eye patching and/or eyeglass therapy, especially if amblyopia (lazy eye) is present. This therapy is designed to maximize the existing vision in the “bad” eye. In some children, this therapy may eliminate the need for surgery.

To correct strabismus, the eye surgeon makes a small incision in the tissue covering the eye and accesses the eye muscles. The appropriate muscles are then repositioned to allow the eye to move properly. The procedure is usually performed under general anesthesia. Recovery time is rapid, and most people are able to resume normal activities within a few days. Following surgery, corrective eyeglasses may be needed, and, in many cases, further surgery is required later to keep the eyes straight.

When a child requires surgery for strabismus, the procedure is usually performed before school age. This is easier for the child and gives the eyes a better chance to work together. As with all surgery, there are some risks. However, strabismus surgery is usually a safe and effective treatment.