Exotropia is a common type of strabismus that occurs when misaligned eyes deviate outward.
Exotropia (also known as wall-eye or divergent strabismus) differs from its opposite form, esotropia (eye turns in toward nose), in that exotropic eyes point outward or away from the nose. Exotropia can occur in one or both eyes. Although exotropia can appear at any age, it commonly appears between the ages of one and four.
Exotropia can be classified according to how frequently the eye deviates:
- Intermittent: Only occurs from time to time; may or may not become more frequent throughout a person’s life; this is the most common form of exotropia.
- Constant: Occurs at all times and at all distances.
Exotropia can also be classified by cause—it can be either congenital (present at birth; also known as infantile exotropia) or acquired. Acquired exotropia is found in females more than males; 63–70 percent of all adult cases are women. It is more common in the Middle East, Africa, and Asia, and at latitudes where there are higher levels of sunlight. It is less common in the United States and Europe.
Forms of acquired exotropia include:
- Sensory: Found in conjunction with an eye with poor vision. Typically, the eye with poor vision cannot work effectively with the other eye, allowing a tendency for the eye to drift outward. This form of strabismus is preventable and can be treated easily with corrective prescription eyeglasses.
- Mechanical: Mechanical exotropia is caused by a restriction or tightness of the muscles controlling the eye (fibrosis of muscle tissue, thyroid myopathy) or a physical obstruction of the extraocular muscles (orbital fracture).
- Acute: Sudden onset exotropia usually in older adults with an underlying disease process such as cranial nerve problems or thyroid disorders. It can also be caused by trauma to the eye muscles or orbit.
- Consecutive: Occurs after strabismus corrective surgery (to correct esotropia). It can develop shortly after surgery or may develop years later.
Other types of exotropia include divergence excess and convergence insufficiency.
Exotropia Signs and Symptoms
In most cases, the first signs of exotropia appear during childhood. Typically, it begins intermittently; occurring while the child is staring into space or daydreaming. The deviation may become more noticeable while the child is staring at something from a distance.
Most strabismic children do not know they have vision problems. Sadly, they think problems such as double vision or nearsightedness are normal and do not express their inability to see clearly because they do not know any better. Because of this, it is important to watch children for symptoms of all eye conditions, including exotropia.
- Excessive rubbing of eyes due to eye strain
- Covering or closing one eye to improve vision
- Increasing sensitivity to light (photophobia)
- Double vision
Intermittent exotropia is detectable after six months of age, and is considered a progressive disorder that can lead to constant exotropia if left untreated.
What Causes Exotropia?
This condition is believed to be connected to some defect involving the six extraocular muscles that control each eye’s movement. Normally, these muscles work together, sending signals to the brain and directing eye movements so that both eyes can focus on the same object.
But when there is a disruption and the muscles do not work together, some form of strabismus, including exotropia, may occur. Other causes may involve the nerves that transmit information from the brain to the muscles, or the part of the brain that directs eye movements. Eye injuries, head trauma, and other general health conditions can also cause exotropia.
Parents and other family members are typically the first people to notice exotropia in a child. Those who develop this condition later in life may notice the change in their eyes’ appearance while looking at old photos of themselves, after experiencing symptoms, and most commonly by having others tell them their eye is turning out
When exotropia is suspected in an infant, the eye doctor will shine a light into the eyes to see if the light reflects back from the same location on each cornea. In older children and adults, the eyes are examined more thoroughly. Several eye exams and visual tests can help your eye doctor determine which form of exotropia is present. These tests may include:
- Ocular Motility Exam: This exam checks your eye’s ability to move in all directions. Your eye doctor will sit in front of you and perform a “follow my finger” test, in which the subject is asked to follow the doctor’s finger as it draws an imaginary double H figure that touches upon the eight fields of gaze.
- Visual Acuity Exam: This exam measures the extent to which your vision may be affected. Typically, you are asked to read letters on distant and close-up reading charts. Normal distance-vision acuity is 20/20.
- Alignment: This exam is to determine how well your eyes work together as a team. There are multiple methods for checking the eye’s alignment, and the most commonly used technique is called the Cover Test. The doctor will cover and uncover each eye while you are focusing on objects at different distances. The degree or magnitude (size) of exotropia can be determined by using a prism.
- Refraction: This exam determines the appropriate prescription lens power you need to compensate for any refractive errors you may have (such as nearsightedness, farsightedness, or astigmatism).
There are many factors your eye doctor takes into consideration when determining the appropriate method of treatment for your exotropia:
- The magnitude (size) of the exotropic deviation (how much the eye turns outward)
- The frequency of the deviation
- The age of the patient
- The refractive error of the patient
- The severity of symptoms the patient is experiencing.
For mild cases of exotropia, eyelasses and/or vision therapy (eye exercises) are the most common treatment methods. Eyeglasses are used to make each eye see as well as possible so that the eyes will work together as a team. Eye exercises benefit those with convergence insufficiency more than those with other types of exotropia.
Most people with intermittent exotropia (the most common form) can learn to recognize the problem and eventually control it with certain techniques taught in vision therapy. Special glasses with prisms can be used to decrease double vision in patients with constant exotropia
In moderate to severe cases in children, an eye patch may be recommended. Typically, eye patches are used for strabismic children who also have amblyopia (decreased vision in one eye). The idea is to get the weaker of the two eyes—the “lazy” eye—seeing as well as the better eye so that both eyes will work together as a team.
If these methods fail, eye muscle surgery may be performed. In general, however, eye muscle surgery is not recommended unless the patient:
- Experiences exotropia more than 50 percent of each day
- Experiences significant symptoms (squinting, eye strain, etc.)
- Experiences an increase in the frequency and duration of episodes
- Experiences significant exotropia when looking at objects that are near
- Appears to be experiencing a decrease in binocular vision (depth perception)
During the procedure, the eye muscle is exposed by making a small incision in the tissue covering the eye. The appropriate muscles are then repositioned in order to allow the eye to move properly. This procedure is usually performed under general anesthesia.
Most people are able to go home the same day as their surgery, and recovery usually takes about two weeks. After surgery, your eye doctor may prescribe pain relievers, antibiotics to fight and prevent infection, and steroidal eye drops or ointment to reduce inflammation. Over-the-counter pain medications are usually allowed, except for aspirin or similar products that may thin the blood.
Your doctor may also recommend that you:
- Avoid getting your eyes wet until told that you may do so
- Avoid swimming for ten days
- Wait one week to resume normal activities
- Wear protective eye wear, especially right after surgery, to compensate for light sensitivity
- Store your eye drops in a refrigerator; do not freeze them
Complications of Exotropia
Untreated exotropia can lead to permanent vision loss in the form of amblyopia or damage to the eye muscles. Intermittent exotropia may progress to constant exotropia.
If surgery is performed, possible complications can include bleeding, surgical wound infections, swelling of the eyelid, and repeat surgeries for recurring exotropia. Exotropia can sometimes recur after surgery. Talk with your doctor about the risks and benefits of eye muscle surgery.
When to Contact Your Doctor
Contact your eye care professional if:
- You develop signs of infection (headache, dizziness, muscle aches, general ill feeling, and fever)
- Pain, swelling, redness, drainage, or bleeding increases in the surgical area
- New, unexplained symptoms appear
- Drugs taken after surgery produce unwanted side effects
- University of Michigan Kellogg Eye Center, Extropia, http://www.kellogg.umich.edu/patientcare/conditions/exotropia.html
- American Association for Pediatric Ophthalmology and Strabismus, Exotropia, http://www.aapos.org/terms/conditions/49