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What is strabismus? | Symptoms | Types | Causes | Consequences | Diagnosis | Treatment

What is strabismus?

Strabismus is the medical term used when both eyes do not focus straight ahead. One eye turns in or out. Normally both eyes aim at the same spot, and the brain fuses the two pictures into one 3-D image. When one eye turns, the brain receives two different pictures that it is unable to fuse into one image. So the brain "turns off" or learns to ignore one of the images. If the child uses only one eye, he or she loses their depth perception.

Misalignment of the eyes may be present all the time, or it may come and go. Strabismus occurs in about four percent of the population, and is found about equally in males and females. It tends to run in families.

Strabismus can occur later in life. If it occurs then, the person has double vision. The brain is already trained to receive images from both eyes and can't ignore one.

Strabismus is common among children with cerebral palsy, Down's syndrome, hydrocephalus, or brain tumors. Injury or cataracts can also cause strabismus.

Symptoms

The main symptom of strabismus is that one eye does not look straight ahead, but wanders off in another direction. It may wander to the left, right, up, or down.

Children sometimes squint one eye in bright sunlight or tilt their head in order to use their eyes together. To get their eyes to work together, children may turn their face to the right or left, tilt their head, or raise or lower their chin. If a child uses an abnormal head position to get his eyes to work together, both eyes generally develop good vision and their binocular function is normal.

Since infants' eyes don't always focus on objects at first, their eyes may appear to move independently. However, by three months, infants should be able to focus on small objects and their eyes should be parallel. By six months, they should be able to focus on objects both near and far.

If a child persistently demonstrates any of the following behaviors, an appointment should be made with an ophthalmologist for an eye examination.

• One eye aims or drifts in a different direction. This may be subtle and is a significant symptom even if it occurs only when a child is tired or stressed.
• The child turns or tilts its head to see.
• The child tilts its head to one side frequently and one shoulder is noticeably higher than the other.
• The child squints or closes one eye.
• The child has poor visual/motor skills (hand-eye coordination).
• The child bumps into things or drops things frequently.

While reading or doing close work, the child:

• Holds the book or object unusually close.
• Closes one eye or covers one eye with his hand.
• Twists or tilts his head toward book or object favoring one eye.
• Loses his place and tires easily.
• Uses a finger to read.
• Rubs his eyes during or after short periods of reading.

The child frequently complains of:

• Headaches or eyestrain.
• Nausea or dizziness.
• Motion sickness.
• Double vision.

If your child is experiencing some of the symptoms described here, it does not necessarily mean your child has strabismus. However, if the child experiences one or more of these symptoms, you should contact your eye doctor for a complete exam. Click here for information on emergency or immediate care.

Types

Esotropia or convergent strabismus is commonly referred to as crossed eyes. In this type of strabismus, one eye turns inward. The child may be born with the condition or it may develop within a few months of birth or about age two. It is the most common form of strabismus in infants.

Surgery to adjust the tension in the eye muscles can be done to align the eyes. Tight inner muscles can be removed from the wall of the eye and moved further back on the eye. This weakens the pull of the muscle and lets the eye move outward to its normal position. The outer muscles can also be shortened to tighten them, allowing the eyes to move out.

Accomodative esotropia occurs in farsighted children two years of age or older. When a child is young, he or she can focus the eyes to adjust for farsightedness, but the focusing effort, or accommodation, makes the eyes cross. Glasses may be prescribed to reduce the focusing effort and can straighten the eyes. The child may need bifocals for close work. Eye drops, ointment, or special lenses called prisms can also be used to straighten the eyes.

Exotropia or divergent strabismus is commonly called "walleye." In this type of strabismus, one eye turns outward. This occurs most often when a child is focusing on distant objects. It often occurs only part of the time, particularly when a child is daydreaming, ill, or tired. The child may squint in bright sunlight. Glasses, exercises, or prisms may reduce or help control the outward turning, but surgery may be needed to correct the problem.

In vertical strabismus, one of the eyes is out of alignment vertically and looks either up or down. In hypertropia, the eye turns up, and in hypotropia, the eye turns downward.

Causes

The tendency for strabismus is inherited. If it runs in the family, the child should be checked very early, even if the eyes appear to be normal.

Strabismus may occur because the eye is out of focus and the child needs glasses.

Strabismus may be the result of a muscle abnormality. Six eye muscles that control eye movement are attached to each eye. Two muscles move the eye right and left, while the other four move it up and down and at an angle. To line the eye up properly and to focus on an object, all six muscles in both eyes must work together. To move together, the muscles must be coordinated.

Strabismus may also be secondary to a more serious condition in the eye such as cataracts.

Consequences

If strabismus is not corrected, the child will have defective binocular vision. For the images coming from each eye to fuse in the brain, the eyes must be straight and work together. If the eyes don't both aim in the same direction and work together, the person will lose his or her three-dimensional vision and depth perception and will develop amblyopia. Amblyopia is the loss of vision in the turned eye. Rather than seeing a double image, the brain will "turn off" the image. If treatment is begun immediately, the child's vision should be able to be saved.

Diagnosis

Strabismus can be diagnosed during an eye exam. All children should have their eyes examined by their pediatrician, family doctor, or ophthalmologist by age 4, earlier if there is a family history of strabismus or amblyopia.

Early in life, babies often demonstrate false strabismus. Their eyes seem to be crossed. Babies have a wide flat nose and folds of skin at their inner eyelid that makes their eyes appear crossed. Generally, they are not crossed, but an ophthalmologist can determine if strabismus exists.

Treatment

The goal of treatment is to restore good vision in both eyes and to restore binocular vision. The normal treatment is to patch the eye that is straight to bring the vision up to normal in the turned eye. The parent has a very important role in treating and correcting strabismus. Children don't like to have their eyes patched, particularly if they have been using the patched eye to see. They want to take the patch off and may be very uncooperative. The parents must convince the child that patching the eye is best for them. The parents must be very involved and able to gain the child's cooperation. The child will need lots of attention, hugging, and support until he or she gets used to the patch. Distraction works best for infants and toddlers. Bribery may also work well for toddlers. Reason generally works with older children.

If there is a focusing problem, treatment may include using glasses to correct the focusing problem and help straighten the eyes.

Surgery may be necessary to correct strabismus. Many people are concerned that the eyeball is removed in this type of surgery, but that is not true. Small cuts are made in the tissue over the eye to reach the muscles. Depending on which way the eyes turn, the muscles are repositioned. A local anesthetic is generally used for adults, while a general anesthetic is used for children.

There is a quick recovery time and the patient is usually able to go back to a regular schedule quickly. Patients may need glasses or prism lenses after surgery.

Sometimes Botox injections are used. This new drug, approved by the FDA, is injected into the eye muscle. It temporarily relaxes the muscle and allows the opposite muscle to tighten and straighten the eye. The effect will wear off after a few months, but the misalignment may be permanently corrected.

Medication (eyedrops or ointment) is sometimes used with or without glasses to help correct strabismus.

Finally, patients are sometimes given eye exercises to teach proper eye coordination.