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What is strabismus?

Strabismus is a visual defect in which the eyes are misaligned and point in different directions.  One eye may look straight ahead, while the other eye turns inward, outward, upward or downward. You may always notice the misalignment, or it may come and go.  The turned eye may straighten at times, and the straight eye may turn. Strabismus is a common condition among children.  About 4% of all children in the United States have strabismus.  It can also occur later in life.
It occurs equally in males and females.  Strabismus may run in families.  However, many people with strabismus have no relatives with the problem.

How do eyes work together?

With normal vision, both eyes aim at the same spot.  The brain then fuses the two pictures into a single, three-dimensional image.  This three-dimensional image gives 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 of the misaligned eye and sees only the image from the straight or better-seeing eye.  The child then loses depth perception. Adults who develop strabismus often have double vision because the brain is already trained to receive images from both eyes and cannot ignore the image from the turned eye.


Good vision develops during childhood when both eyes have normal alignment.  Strabismus may cause reduced vision, or amblyopia, in the weaker eye. The brain will recognize the image of the better-seeing eye and ignore the image of the weaker or amblyopic eye.  This occurs in approximately half the children who have strabismus. Amblyopia can be treated by patching the “good” eye to strengthen and improve vision in the weaker eye.  If amblyopia is detected in the first few years of life, treatment is usually successful.
If treatment is delayed until later, amblyopia usually becomes permanent.  As a rule, the earlier amblyopia is treated, the better the visual result. 

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’s syndrome
  • Hydrocephalus
  • Brain tumors

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

What are the symptoms of strabismus?

The main symptoms 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. 

How is strabismus diagnosed?

Strabismus can be diagnosed during an eye exam.  It is recommended that all children have an eye exam by an ophthalmologist (Eye MD) 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.
A child will not outgrow true 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.