The term congenital exotropia is typically reserved for patients presenting in the first year of life with a large, constant angle.
However, as Hunter et al (2001) state, no published study provides a rationale for this restrictive definition.[1] In their study, they evaluated differences between infants, aged younger than 1 year, with constant exotropia versus intermittent exotropia at presentation.[1] They found that "half of infantile exotropia patients may present with intermittent exotropia, with similar clinical outcomes regardless of presentation."[1] In their study, surgical intervention resulted in successful alignment in most cases.[1] More than half the patients developed measurable stereopsis, but none achieved bifixation.[1]
In a 2008 study of 12 patients with intermittent exotropia treated with bilateral lateral rectus recession, stereoacuity, as seen in the late follow-up period, measured at 40 arcsec in 2 patients, 100 arcsec in 3 patients, 140-400 arcsec in 2 patients, and none in 5 patients.[2]
True congenital exotropia (with a fixed exotropia) is an extremely rare form of strabismus and may occur with systemic disease in as many as 60% of patients. Patients with craniofacial syndromes, ocular albinism, midline defects, and cerebral palsy may present with congenital exotropia.
See related CME at Highlights of the American Association for Pediatric Ophthalmology and Strabismus Annual Meeting.
The pathophysiology is unknown, although strabismus does occur in families, suggesting a multifactorial autosomal dominant pattern with incomplete penetrance.
A good recent review of risk factors and genetics in common comitant strabismus can be found here.[3]
United States
Congenital exotropia is extremely rare in the United States.
International
The worldwide incidence of congenital exotropia is unknown.
There is a higher incidence of amblyopia in congenital exotropia than in other forms of exotropia.
No known racial predisposition to congenital exotropia exists.
No known sexual predilection exists.
Congenital exotropia presents in infants younger than 6 months. Children who are born premature are at higher risk of developing strabismus; however, congenital exotropia does not occur at a higher rate in premature children.
By definition, children present when they are younger than 12 months with a constant outward deviation of the eyes.
Unlike other neurologic forms of exotropia, there should be no pupillary or lid involvement. Although craniofacial syndromes can be seen with congenital exotropia, there should be no ptosis or pupillary mydriasis (see Oculomotor Nerve Palsy).
The eyes should appear diverging with no limitation of adduction.
Over time, a preference may occur with one eye used consistently for fixation; then, the other eye will develop amblyopia.
As many as 60% of patients may develop oblique muscle dysfunction, dissociated vertical deviation, and amblyopia. Nystagmus is rare.
There is a familial predisposition suggestive of an autosomal dominant pattern with incomplete penetrance.
Radiographic imaging is indicated if neurologic signs and/or craniofacial anomalies are present.
High-resolution MR imaging enables direct imaging of the ocular motor nerves. In a cohort of 247 consecutive patients with strabismus, Kim et al demonstrated ocular motor nerve abnormalities by high resolution MRI in 98/112 (88%) of patients with congenital or developmental neuropathic strabismus.[4]
Chromosomal studies may be performed if any other facial or systemic anomalies are present.
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A child with any form of strabismus is at risk of losing vision (amblyopia). Since these children present at a nonverbal age, it is imperative that a pediatric ophthalmologist screen and follow the visual status during the critical years of visual development.
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