|Strabismus, also known as "crossed" or "misaligned" eyes, causes double vision.
Crossed eyes – medically known as strabismus (struh-BIZ-mus) – refer to a condition in which muscles that control eye movement are not properly coordinated or by problems with the nerves that control the eye muscles or with the brain where the signals for vision are processed. The result is one or both eyes turn inward, outward, upward or downward, or one or both eyes may move irregularly.
Also known as “misaligned eyes,” “wandering eyes” or “wall eyes,” strabismus can be constant or occur intermittently, which usually worsens when eye muscles are tired or during illness. When the eyes turn inward toward the nose (or crossed), the condition is called “esotropia” – the most common form. When they turn outward, it is called “exotropia.” When an eye turns upward it is known as “hypertropia” and “hypotropia” refers to an eye turned downward.
Strabismus is usually diagnosed during childhood and affects about 4 percent of children, afflicting boys and girls equally. But it can develop in older children or adults as the result of injury or diseases such as a brain disorder, diabetes, high blood pressure, multiple sclerosis or thyroid problems.
Most infants appear to be crossed-eyed, at least intermittently, during their first 3 months, as they are learning to focus. Most babies outgrow this. If your child’s eyes remain crossed or misaligned after 6 months, it may be infantile esotropia, a condition that often results from heredity or cerebral palsy. However, a condition often mistaken for strabismus is pseudostrabismus, in which a widened nasal bridge or extra fold of skin makes the white sclera appear less visible – giving the appearance that the eyes are crossed. This usually resolves as the infant grows and the facial structures change.
The obvious signs of strabismus are eyes that appear misaligned and don’t move together. Those with strabismus may experience:
- Double vision
- Difficulty focusing or judging distances
- Frequent blinking or squinting, especially in bright sunlight
- Tilting the head to look at things
- Frequent headaches
- Eye pain
Strabismus cannot be prevented, but its complications can be avoided with early intervention. Even if you notice symptoms intermittently – when your child is ill, stressed or fatigued – alert your eyecare provider or pediatrician. Children should be monitored closely prior to entering school, especially if strabismus runs in your family. Most experts recommend an eye exam for all children before age 6 months, and then annually starting around age 3.
Uncorrected strabismus represents one of the leading causes of vision loss and blindness in children. Generally, the younger children are when treated, the shorter the course of treatment and the higher the likelihood of success.
After infancy, children will not “outgrow” strabismus so the condition must be treated as soon as possible. When diagnosed early, correction is usually successful. But left uncorrected, strabismus can lead to
(lazy eye) and permanent loss of depth perception.
Before treatment is implemented, the precise cause should be determined. Crossed eyes can be indicative of other serious conditions such as diabetes, high blood pressure, and neurological disorders. Because there are many causes, treatment often involves a combination of elements including eyeglasses, vision therapy (orthoptics), surgery and medication.
Eyeglasses help redirect the line of sight, improve focusing ability, relieve some of the symptoms, and encourage the eyes to straighten.
- Vision therapy, or orthoptics, train the eyes to work together, often with the use of an eye patch.
- Surgery is sometimes required to reposition the eye muscles and restore permanent control of the eyes. Frequently, repeat surgery must be performed to keep the eyes aligned. Vision therapy and corrective glasses may be prescribed before and after surgery.
- Drug therapy is controversial and usually considered a "last resort" treatment. Anticholinesterase miotics are eye drops or ointment that can enhance the focusing mechanisms of the eye. These are used on both children and adults, but have potential side effects such as including headaches, tearing, blurred or clouded vision, and decreased night vision. Botulinum toxin type A may offer an alternative to eye-muscle surgery, but this drug is rarely used on children, as it it injected into an eye muscle to paralyze it, allowing the opposing muscle to tighten and straighten the eye. The effects of the muscle paralysis wears off, but the eye may be permanently corrected.
Side effects may include drooping of the eyelid, and loss of vertical eye movement.
Due to the high risk of recurrence and complications, children with strabismus must be closely monitored long term. Patching may continue throughout childhood.
If strabismus is not treated during childhood, the likelihood of correction is low. Treatment in pre-adolescents, adolescents and adults is possible but takes longer and is less effective. In adults, treatment may not improve eyesight at all. The condition may have progressed into lazy eye, a condition in which the nerves that transmit signals from the eye to the brain degenerate and cause permanent vision loss. Surgery to realign the muscles and straighten the eyes may be performed for cosmetic reasons only.