Strabismus

Strabismus may appear in the first few months of life or later in childhood, depending on the cause.

In children under 6 months of age, risk factors for strabismus include family history of strabismus, genetic disorders (such as Down syndrome), exposure to medications or other substances that a pregnant woman takes during pregnancy (including alcohol), prematurity, birth defects of the eyes, and cerebral palsy.

In children 6 months of age or older, strabismus is often caused by a refractive error (excessive farsightedness [hyperopia]) or an imbalance in the pull of muscles that control the position of the eyes. Severe vision loss in one eye (due to refractive error or less common disorders such as cataracts) can cause strabismus because it interferes with the brain’s ability to maintain the alignment of the eyes. Other causes include retinoblastoma (a type of eye cancer); neurologic conditions such as increased pressure in the skull, cerebral palsy, spina bifida, and weakness of cranial nerves that control eye movement; head injury; and viral infection of the brain (encephalitis). Sometimes a fracture of the eye socket can block movement of the eye and cause strabismus.

There are several types of strabismus. Some types are characterized by inward turning of the eye (esotropia or cross-eye) and some by outward turning of the eye (exotropia or walleye). Other types are characterized by upward turning of the eye (hypertropia) or downward turning of the eye (hypotropia). The defect in alignment may be constant (the eye turns all of the time) or intermittent (the eye turns only some of the time) and may be mild or severe.

Strabismus: A Misaligned Eye

There are several types of strabismus. In the most common types, an eye turns inward (esotropia or cross-eye, top) or outward (exotropia or walleye, bottom). In this illustration, the child's right eye is affected.

Strabismus (Esotropia)

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This photo shows a child who has a type of strabismus called esotropia. The child's left eye turns inward toward the right eye.

DR P. MARAZZI/SCIENCE PHOTO LIBRARY

A phoria is an unseen, minor misalignment of the eyes. This misalignment is easily corrected by the brain to maintain apparent alignment of the eyes and allow fusion of the images from both eyes. Thus, phorias usually do not cause symptoms and do not need treatment unless they are large and decompensate, causing double vision (diplopia).

A tropia is a constant, visible deviation or misalignment of one eye or both eyes. An intermittent eye deviation that is frequent and poorly controlled by the brain is termed intermittent tropia.

Parents sometimes notice strabismus because the child squints or covers one eye. The defect may be detected by observing that the child's eyes appear to be positioned abnormally or do not move in unison.

Unless severe, phorias rarely cause symptoms. If they do cause symptoms, phorias typically cause eye strain.

Tropias sometimes cause symptoms. Younger children frequently lose vision in one eye (amblyopia) because their brain suppresses the image from the misaligned eye to avoid confusion and double vision. Older children may have double vision or they may have twisting or spasm of the neck (torticollis) to compensate for the misaligned eyes.

• Eye examination

• Sometimes imaging tests

Children should be examined periodically to measure vision and to detect strabismus starting at a few months of age. To examine an infant, a doctor shines a light into the eyes to see whether the light reflects back from the same location on each pupil.

Older children can be examined more thoroughly. Children may be asked to recognize objects or letters with one eye covered and to participate in tests to assess alignment of the eyes. All children with strabismus require examination by an eye doctor who specializes in the evaluation and treatment of all types of eye disorders (ophthalmologist). (See also The Eye Examination.)

Doctors may do imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI), of the brain or spinal cord in children with cranial nerve palsies. In addition, blood tests may be done to look for genetic disorders.

• Treatment of amblyopia if present

• Eyeglasses or contact lenses

• Eye exercises

• Surgery to align the eyes

If the defect is minor or intermittent, treatment may not be needed. However, if strabismus is severe or is progressing, treatment is required.

Treatment of strabismus depends on the characteristics and cause of the strabismus. Treatment is first aimed at equalizing vision (that is, correcting amblyopia).

Doctors equalize vision by encouraging the child to use the weaker eye by putting a patch over the better eye (patching) or using eye drops to blur the vision in the better eye. Patching or using eye drops in the better eye allows the weaker eye to get stronger. Patching is not, however, a treatment for strabismus.

For children with significant refractive error, doctors usually prescribe eyeglasses or contact lenses.

Sometimes eye exercises can help correct intermittent exotropia.

If these nonsurgical methods are unsuccessful in aligning the eyes satisfactorily, the eyes are aligned surgically. Surgical repair consists of loosening (recession) and tightening (resection) of the eye muscles. Children usually are not hospitalized for this procedure. The procedure can cause complications, the most common of which are correction beyond what is needed (overcorrection) or correction below what is needed (undercorrection) and strabismus that returns later in life. Rarely, children may develop an infection, excessive bleeding, or vision loss after the procedure.

Strabismus should not be ignored or watched on the assumption that it will be outgrown. Permanent vision loss can occur if amblyopia occurs and is not treated promptly. Children treated at a later age can improve with treatment, but once the visual system has matured (typically by age 8), response to treatment is minimal. As a result, all children should have periodic formal vision screenings during the preschool years.

Success rates with surgical repair of strabismus can be greater than 80%. About 20% of children need another surgical procedure.

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

1. Children's Eye Foundation of AAPOS: Practical information about prevention, detection, research, and education to protect the vision of children