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Strabismus

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What is strabismus?

The main symptom of strabismus is an eye that is not straight. Sometimes children will squint one eye in bright sunlight or tilt their head to use their eyes together.

What causes strabismus?

The exact cause of strabismus is not fully understood. Six eye muscles, controlling eye movement, are attached to the outside of each eye. In each eye, two muscles move the eye right or left. The other four muscles move it up or down and at an angle. To line up and focus both eyes on a single target, all of the muscles in each eye must be balanced and working together. In order for the eyes to move together, the muscles in both eyes must be coordinated. The brain controls the eye muscles. Strabismus is especially common among children with disorders that affect the brain, such as:

  • Cerebral palsy;
  • Down syndrome;
  • Hydrocephalus;
  • Brain tumors.

A cataract or eye injury that affects vision can also cause strabismus.

How is strabismus diagnosed?

Strabismus can be diagnosed during an eye exam. It is recommended that all children have their vision checked by their pediatrician, family doctor or ophthalmologist (medical eye doctor) at or before their fourth birthday. If there is a family history of strabismus or amblyopia, an ophthalmologist can check vision even earlier than age three. The eyes of infants often seem to be crossed. Young children often have a wide, flat nose and a fold of skin at the inner eyelid that can make the eyes appear crossed. This appearance of strabismus may improve as the child grows. A child will not outgrow true strabismus. An ophthalmologist can usually tell the difference between true and false strabismus.

How is strabismus treated?

Treatment for strabismus works to: Preserve vision; Straighten the eyes; Restore binocular (two-eyed) vision.

After a complete eye examination, an ophthalmologist can recommend appropriate treatment. In some cases, eyeglasses can be prescribed for your child. Other treatments may involve surgery to correct the unbalanced eye muscles or to remove a cataract. Covering or patching the strong eye to improve amblyopia is often necessary.

Most common types of Strabismus:

    Esotropia

    Esotropia, where the eye turns inward, is the most common type of strabismus in infants. Young children with esotropia do not use their eyes together. In most cases, early surgery can align the eyes. During surgery for esotropia, the tension of the eye muscles in one or both eyes is adjusted. The tight inner muscles may be removed from the wall of the eye and placed further back on the eye. This adjustment weakens their pull and allows the eyes to move outward. Sometimes the outer muscles are tightened by shortening the muscle length to allow the eyes to move outward.

    Accommodative esotropia

    Accommodative esotropia is a common form of esotropia that occurs in farsighted children two years or older. When a child is young, he or she can focus the eyes to adjust for the farsightedness, but the focusing effort (accommodation) to see clearly causes the eyes to cross. Glasses reduce the focusing effort and can straighten the eyes. Sometimes bifocals are needed for close work. Eye drops, ointment or special lenses called prisms can also be used to straighten the eyes.

    Exotropia

    Exotropia, or an outward turning eye, is another common type of strabismus. This occurs most often when a child is focusing on distant objects. The exotropia may occur only from time to time, particularly when a child is daydreaming, ill or tired. Parents often notice that the child squints one eye in bright sunlight. Although glasses, exercises or prisms may reduce or help control the outward turning eye in some children, surgery is often needed.

How is strabismus surgery done?

The eyeball is never removed from the socket during any kind of eye surgery. The ophthalmologist makes a small incision in the tissue covering the eye to reach the eye muscles. Certain muscles are repositioned during the surgery, depending on which direction the eye is turning. It may be necessary to perform surgery on one or both eyes. When strabismus surgery is performed on children, a general anesthetic is required. Local anesthesia is an option for adults.

Recovery time is rapid. People are usually able to resume their normal activities within a few days.After surgery, glasses or prisms may be useful. In many cases, further surgery may be needed at a later stage to keep the eyes straight.

For children with constant strabismus, early surgery offers the best chance for the eyes to work well together. In general, it is easier for children to undergo such surgery before school age. As with any surgery, eye muscle surgery has certain risks. These include infection, bleeding, excessive scarring and other rare complications that can lead to loss of vision. Strabismus surgery is usually a safe and effective treatment for eye misalignment. It is not, however, a substitute for glasses or amblyopia therapy.

Injections

Botox (TM), a new drug approved by the U.S. Food and Drug Administration for limited use, is an alternative to eye muscle surgery for some individuals. An injection of this drug into an eye muscle temporarily relaxes the muscle, allowing the opposite muscle to tighten and straighten the eye. Although the effects of the drug wear off after several weeks, in some cases, the misalignment may be permanently corrected. Material reproduced from The American Academy of Ophthalmology

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