Strabismus

Overview

Strabismus is a disorder where the eyes are misaligned, i.e. point in different directions. While one eye looks straight ahead, the other eye may be turned inward, outward, up or down. This misalignment may be present constantly, or may come and go.

Strabismus is a common condition among children. Approximately 4% of children in the United States have strabismus. Strabismus may also occur in adults (see "Strabismus in adults").

The exact cause of strabismus is not completely understood. Each eye has six muscles that work together to control eye movements, with the brain controlling these muscles in order to keep the eyes properly aimed at the same spot. The brain fuses the images from both eyes into a single three-dimensional image, giving us depth perception. When one eye turns, two different pictures are sent to the brain. In a young child, the brain learns to ignore the image from the misaligned eye and sees the image only from the straight or better-seeing eye. This can lead to amblyopia ("lazy eye") and loss of depth perception. Adults who develop strabismus typically complain of double vision because the brain is already trained to receive images from both eyes and can not ignore the image from the misaligned eye.

Signs and Symptoms

• Turned or crossed eye
• Double vision (in some cases)
• Head tilt or turn
• Squinting

It is unusual for a child to complain of double vision. This is one reason why children should undergo vision screening exams. The younger the child is when strabismus is detected and treated, the better the chance of normal vision.

Types of Strabismus

There are numerous forms that strabismus may take, depending upon which way the eye turns, the underlying cause (if any), and associated syndromes. The two most common categories are esotropia and exotropia. Esotropia occurs when one eye is turned towards the nose. This inward deviation of the eyes can begin in infancy or later in childhood. Exotropia occurs when one eye turns outward. It typically begins around age 2 to 4 years, but can begin at any age.

Adult Strabismus

Most cases of strabismus in adults occur as a result of a vascular insult ("ministroke") to a nerve that controls the movement of one or more eye muscles. This is most often seen in older adults who have a history of diabetes or high blood pressure. Most of these cases get better with time.

Strabismus may also occur in adults who previously had strabismus as a child. This may occur as a result of an inability to control eye movements as well as in the past, or for other unknown causes.

The treatment of strabismus in an adult depends on the cause. As previously mentioned, many cases may resolve over time. Small deviations can often be treated with prism ground into eyeglasses; the prism redirects the misaligned images entering the eye to eliminate the double vision. Other cases will require eye muscle surgery to realign the eyes.