Strabismus is a visual problem in which the eyes are not aligned properly and point in different direction, a common condition among children. About 4 percent of all children in the United States have strabismus. It can also occur later in life. It may run in families; however, many people with strabismus have no relatives with the problem. One eye may look straight ahead, while the other eye turns inward, outward, upward, or downward. The eye turn may be consistent, or it may come and go. Which eye is straight (and which is misaligned) may switch or alternate.
Causes
Each eye has six external muscles (called the extraocular muscles) that control eye position and movement. For normal binocular vision, the position, neurological control and functioning of these muscles for both eyes must be coordinated perfectly.
Strabismus occurs when there are neurological or anatomical problems that interfere with the control and function of the extraocular muscles. The problem may originate in the muscles themselves, or in the nerves or vision centers in the brain that control binocular vision.
Genetics also may play a role: If you or your spouse has strabismus, your children have a greater risk of developing strabismus as well.
Occasionally, when a farsighted child tries to focus to compensate for uncorrected farsightedness, he or she will develop a type of strabismus called accommodative esotropia, where the eyes cross due to excessive focusing effort. This condition usually appears before 2 years of age but also can occur later in childhood. Often, accommodative esotropia can be fully corrected with eyeglasses or contact lenses.
Treatment
In most cases, the only effective treatment for a constant eye turn is strabismus surgery. If your general eye doctor finds that your child has strabismus, he or she can refer you to an ophthalmologist who specializes in strabismus surgery.
In most cases, the only effective treatment for a constant eye turn is strabismus surgery.
The success of strabismus surgery depends on many factors, including the direction and magnitude of the eye turn. In some cases, more than one surgery may be required. The strabismus surgeon can give you more information about this during a pre-surgical consultation.
Strabismus surgery also can effectively align the eyes of adults with long-standing strabismus. In many cases of adult strabismus, however, a significant degree of amblyopia may remain even after the affected eye is properly aligned. This is why early treatment of strabismus is so important.
The earlier strabismus is treated surgically, the more likely it is that the affected eye will develop normal visual acuity and the two eyes will function together properly as a team.
Non-Surgical Strabismus Treatment
In some cases of intermittent and small-angle strabismus, it may be possible to improve eye alignment non-surgically with vision therapy.
For example, convergence insufficiency (CI) is a specific type of intermittent exotropia in which the eyes usually align properly when viewing a distant object, but fail to achieve or maintain proper alignment when looking at close object, such as when reading, resulting in one eye drifting outward. Convergence insufficiency can interfere with comfortable reading, causing eye strain, blurred vision, double vision and headaches.
There also is some evidence that suggests CI can cause attention problems and affect academic performance in children. A recent study conducted by Mayo Clinic researchers found that children with exotropia (including convergence insufficiency) at an early age were significantly more likely to develop attention deficit hyperactivity disorder (ADHD), adjustment disorder and learning disabilities by early adulthood.
Certain types of strabismus also have been associated with an increased risk of myopia. Another Mayo Clinic study published in 2010 followed 135 children with intermittent exotropia over a 20-year period and found that more than 90 percent of these children became nearsighted by the time they reached their 20s.
On the bright side, it appears non-surgical vision therapy can be an effective treatment for convergence insufficiency. In a study published in Archives of Ophthalmology, 73 percent of 221 children with symptomatic convergence insufficiency had a successful or improved outcome following a 12-week program of office-based vision therapy combined with eye exercises performed at home.
Sometimes, a strabismus surgeon may recommend a program of vision therapy for a period of time after strabismus surgery to treat amblyopia and minor binocular vision problems that might remain after surgery. In these cases, the term “orthoptics” (“ortho” = straight; “optics” = eyes) rather than “vision therapy” might be used to describe this treatment, which may be provided by an orthoptist working closely with the surgeon rather than by an optometrist.