Strabismus

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Chapter 41 STRABISMUS

Theodore X. O’Connell

General Discussion

Strabismus refers to ocular misalignment and is one of the most common reasons for referral of pediatric patients to ophthalmologists. Strabismus includes a heterogeneous group of eye movement problems ranging from constant to latent, and from congenital to those acquired late in life. The ocular misalignment present in strabismus interferes with the development and use of normal binocular vision and results in permanent loss of stereopsis (depth perception) if the eyes are not realigned early in development. Strabismus may also interfere with the ability to fix visually on objects of regard and to follow moving objects.

Before 6 weeks of age, coordination of eye movements is poor, and the eyes in normal infants may be misaligned. In fact, the eyes of most children are mildly exotropic (deviating outward). By the age of 3 months, infants’ alignment is stable, and abnormalities of alignment may be diagnosed more accurately. Any strabismus occurring after age 3 months is abnormal.

Infantile strabismus is defined as constant misalignment present before 6 months of age. Infantile strabismus includes infantile esotropia (inward deviation) and exotropia (ouward deviation).

Infantile esotropia is not always observed at birth but is readily apparent by three months of age. There is frequently a family history of strabismus, and this type of strabismus is not usually associated with any other neurologic or developmental problems. Infants with congenital esotropia must be treated before two years of age for optimal visual outcome. Therefore, early detection and treatment of strabismus are essential to maximize potential visual function. The treatment for infantile esotropia usually consists of surgery to realign the eyes. Early surgical realignment appears to result in better outcomes than does later intervention.

Infantile exotropia is much less common than esotropia and is seen frequently in association with cerebral palsy, prematurity, structural abnormalities in an eye, craniofacial syndromes, and other neurodevelopmental conditions. Any exotropia that occurs after the age of 4 months is abnormal. The treatment of infantile exotropia also consists of surgery to realign the eyes, though the outcomes depend on the associated conditions.

Accommodative esotropia (also known as acquired esotropia) occurs after 6 months of life in patients with refractive errors requiring a greater than normal amount of accommodation and in patients with inherently excessive reflexive convergence. This is the most common type of childhood esotropia. Accommodative esotropia appears in children from 6 months to 7 years of age, although it is most common between 2 and 3 years of age. Children with this condition are usually more farsighted than are children without the condition. Treatment consists of glasses to correct refractive error and reduce the need for accommodation. Surgery may be required if other measures do not realign the eyes and also is required for children with esotropia who are not farsighted.

Intermittent exotropia occurs in children after the age of 6 months and occurs when the child looks at distant objects or when the child is fatigued. The eyes may be completely straight when the child looks at near objects. The parents may report observing the child habitually closing the nondominant eye when outdoors. Intermittent exotropia does not routinely require treatment because vision and stereopsis may be normal under usual circumstances. However, patients with more frequent or consistent intermittent exotropia and patients who regress to constant exotropia may require intermittent patching, eyeglasses, vision therapy, or surgery to regain binocular vision.

Pseudoesotropia occurs when the eyes appear crossed as the result of broad epicanthal folds, a wide nasal bridge, or narrow-set eyes. The eyes may appear crossed because of the small amount of sclera that is visible nasally compared with temporally, especially when the child looks to the side. Caution should be exercised in making this diagnosis, however, as true strabismus may coexist with pseudoesotropia.

New-onset strabismus in a school-age child is unusual and warrants neurologic evaluation. Most cases of strabismus in this age group are the result of recurrence of a partially treated strabismus earlier in life.

Key Physical Findings

Corneal light reflex test. With the infant fixating on the light and the observer directly behind the light, displacement of the light reflex from the center of the pupil demonstrates abnormal alignment of the eyes.

Alternate cover test

Suggested Work-Up

Referral to an ophthalmologist is recommended when strabismus is noted in a pediatric patient.

1. Donahue S.P. Pediatric strabismus. N Engl J Med. 2007;356:1040–1047.

2. Mills M.D. The eye in childhood. Am Fam Physician. 1999;60:907–918.

3. Ticho B.H. Strabismus. Pediatr Clin North Am. 2003;50:173–188.

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