Topics:

• What Is Strabismus?
• Vision and the Brain
• Amblyopia
• Causes and Symptoms of Strabismus
• Detection and Diagnosis
• Treatment 
• Strabismus Surgery

What Is Strabismus?

Strabismus is a visual defect in which the eyes are misaligned and point in different directions.  The misalignment may always be noticeable, or it may come and go.  One eye may be directed straight ahead, while the other eye is turned inward, outward, upward, or downward.  The turned eye may straighten at times and the straight eye may turn.

Strabismus is a common condition among children, affecting about four percent, but can also occur later in life.  It occurs equally in males and females and may run in families.  However, many people with strabismus have no relatives with the problem.

Vision and the Brain

When one eye turns, as in strabismus, two different pictures are sent to the brain.  In a young child, the brain learns to ignore the image of the misaligned eye and see only the image from the straight or best seeing eye.  this causes loss of depth perception and binocular vision.  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.

Amblyopia

Normal alignment of both eyes during childhood allows good vision to develop in each eye.  Abnormal alignment, as in strabismus, may cause reduced vision or amblyopia.  The brain will recognize the images 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 preferred or better seeing eye to strengthen and improve vision in the weaker eye.  If amblyopia is detected in the first few years of life, treatment is often successful.  If adequate treatment is delayed until later, amblyopia or reduced vision generally becomes permanent.  As a rule, earlier amblyopia is treated, the better the visual result.

Causes and Symptoms of Strabismus

The exact cause of the eye misalignment that leads to 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 control tilting movements.  to line up and focus both eyes on a single target, all eye muscles of each eye must be balanced and working together with the corresponding muscles of the opposite eye.

The brain controls the eye muscles which explains why children with disorders that effect the brain, such as cerebral palsy, Down's syndrome, hydrocephalus, and brain tumors often have strabismus.  A cataract or eye injury that effects vision can also cause strabismus.

The primary symptom of strabismus is an eye that is not straight.  Sometimes a youngster will squint one eye in bright sunlight or tilt their head in a specific direction to use their eyes together.  Signs of faulty depth perception may also be noticed. 

Detection and Diagnosis

Children should be examined by the family doctor, pediatrician, or ophthalmologist (a medical eye doctor) during infancy and preschool years to detect potential eye problems.  This is particularly important if a relative has had strabismus or amblyopia.

In infants it is often difficult to determine the difference between eyes that appear to be crossed and true strabismus.  Young children often have a wide, flat nose and a fold of skin at the inner eyelid that tends to hide the eye during side gaze, causing the eyes to appear crossed.  This appearance of strabismus may improve as the child grows.  True strabismus is not outgrown. An ophthalmologist can readily distinguish true from false strabismus.  

Treatment 

Treatment goals for strabismus are to preserve vision, to straighten the eyes, and to restore binocular vision.  Depending on the cause of the strabismus, treatment may involve repositioning the unbalanced eye muscle, removing a cataract, or correcting other conditions which are causing the eyes to turn.  After a complete eye examination, including a detailed study of the inner parts of the eye, an ophthalmologist can recommend appropriate optical, medical or surgical therapy.  Covering or patching the good eye to improve vision in the amblyopic eye is often necessary.

Strabismus Surgery

The eyeball is never removed from the socket during any kind of eye surgery.  Strabismus surgery involves making a small incision in the tissue covering the eye which allows the ophthalmologist access to the underlying eye muscles.  Which eye muscles are repositioned during the surgery depends upon the 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.  Over-or-under correction can occur and further surgery may be needed. 

Early surgery is recommended to correct strabismus because younger infants can develop normal sight and binocular vision once the eyes are straightened.  As a child gets older, the chance of developing normal sight and binocular vision decreases.  Crossed eyes can also have a negative effect on a child's self-confidence.

As with any surgery, eye muscles surgery has certain risks.  These include infection, bleeding, excessive scarring, and other rare complications that can lead to loss of vision.  However, strabismus surgery is usually a safe and effective treatment for eye misalignment.  It is not, however, a substitute for glasses or amblyopia therapy.