Section 23. Children's Health Issues

Chapter 277. Eye Disorders

Topics: Introduction | Amblyopia | Strabismus

Strabismus

Strabismus (squint, cross-eyes, wandering eye) is a misalignment or wandering of one eye so that its line of vision is not pointed at the same object as the other eye.

The causes of strabismus are varied and include an imbalance in the pull of muscles that control the position of the eyes or poor vision in one eye.

See the figure Strabismus: A Misaligned Eye.

There are several different types of strabismus, each developing in different ways. Some types of strabismus are characterized by inward turning of the eye (esotropia) and some by outward turning (exotropia). Others are characterized by upward turning (hypertropia) or downward turning (hypotropia).

Parents sometimes notice strabismus because the child's eyes appear to be positioned abnormally. Strabismus may cause double vision (diplopia) in the older child or amblyopia in the younger child.

The child should be examined periodically to detect strabismus, beginning at the age of a few months. To examine an infant, a doctor shines a light into the eyes to see if the light reflects back from the same location on each pupil. Older children can be examined more thoroughly; they may be asked to stare at objects, sometimes with one eye covered. The more thorough examination may reveal mild strabismus that would otherwise be impossible to detect. Children with strabismus need frequent examinations by an eye doctor.

If strabismus is mild, treatment may not be needed. However, if strabismus is severe or worsening, treatment is usually required. Treatment depends on the particular characteristics of the strabismus.

Phoria is a tendency for misalignment of the eyes. The tendency is so minor that, for most of the day, the eye muscle and brain can completely correct any misalignment and maintain fusion. Phoria usually does not cause symptoms, but if sufficiently severe, it can lead to strabismus and double vision. Eye doctors can perform tests to diagnose phoria. Usually, no treatment is needed for phorias without symptoms.

Infantile Esotropia: Infantile esotropia is inward turning of the eyes that develops before 6 months of age; it often runs in families and tends to be severe. The eyes often begin to turn in by 3 months of age. The inward turning tends to be constant and is easily noticeable.

Surgery, which is accomplished by changing the pull of the eye muscles, is usually needed to realign the eyes. Repeated operations may be necessary. Rarely, even the best possible treatment may not fully correct strabismus. Occasionally, amblyopia can develop by the age of 2, even with treatment.

Accommodative Esotropia: Accommodative esotropia is inward turning of the eyes that develops between the ages of 6 months and 7 years, most often in 2- to 3-year-olds and is related to optical focusing (accommodation) of the eyes.

The misalignment is the result of how the eyes move when focusing on nearby or distant objects. Children with accommodative esotropia are often farsighted. Although everyone's eyes turn inward when focusing on very close objects, eyes that are farsighted also turn inward when looking at distant objects. In mild cases, the eyes may turn too far inward only when looking at nearby objects. In more severe cases, the eyes turn too far inward all the time. With treatment, accommodative esotropia can usually be corrected. The first treatment tried is usually eyeglasses, which can help the child focus on objects, reducing the tendency for the eyes to turn inward when viewing those objects. Many children outgrow farsightedness and eventually do not need eyeglasses.

Occasionally, drugs (such as echothiophate eye drops) are used to help the eyes to focus on nearby objects. If eyeglasses and eye drops fail to properly align the eyes, surgery may help. Permanent amblyopia develops less often in children with accommodative esotropia than in children with infantile esotropia.

Paralytic Strabismus: In paralytic strabismus, one or more of the eye muscles that move the eye in a different direction become paralyzed. As a result, the muscles no longer work in balance. The eye muscle paralysis is usually caused by a disorder affecting the nerves to the eye muscles. For example, brain injuries or tumors can increase pressure within the skull, compressing nerves to the eye muscles.

In children with paralytic strabismus, movement of the affected eye is impaired only when the eye tries to move in a specific direction, not in all directions. Amblyopia or double vision may develop. The double vision is made worse by looking in directions normally controlled by the paralyzed eye muscles.

Paralytic strabismus may be treated with eyeglasses that contain prism lenses, which bend the light so that both eyes receive nearly the same image. It may heal by itself over time. Alternatively, surgery may be needed. If paralytic strabismus results from another condition affecting the nerves, such as a brain tumor, the other condition also needs to be treated.

Intermittent Exotropia: Exotropia is outward turning of the eyes. The eyes turn out only sometimes (intermittently), usually when the child is looking at distant objects. Intermittent exotropia is detectable after the age of 6 months.

Intermittent exotropia that does not cause troublesome symptoms, such as double vision, may not need treatment. Amblyopia rarely develops. If symptoms are occasionally troublesome, eyeglasses may help. Rarely, a doctor may recommend exercises for the eye muscles. If symptoms worsen despite the use of eyeglasses, surgery may be effective.