Background
Exotropia is a disorder of eye alignment with one or both eyes deviated outwards relative to their normal relative position causing visual impairment. Congenital exotropia, also known as infantile exotropia, is a rare manifestation of this disease presenting in patients less than 6 months of age. [13]
Congenital exotropia could arguably be subdivided in exotropia in an otherwise healthy patient or found in a patient with other systemic diseases. Constant congenital exotropia may occur with systemic disease in as many as 60% of patients. Patients with craniofacial syndromes, ocular albinism, midline defects, cerebral palsy, and genetic syndromes may present with congenital exotropia. A recent study has shown that earlier age of onset has been associated with a worse visual acuity prognosis. [14]
Pathophysiology
The pathophysiology of congenital exotropia is unknown currently. Exotropia occurs due to a difference in muscular tone between antagonistic ocular muscles with the tone of the lateral muscle overpowering the tone of the medial muscle.
The development of congenital exotropia may be due to aberrant development of the muscle fibers themselves, creating fibrosis and weakness in the muscle to create proper alignment. [15] The outward alignment could also result from a deficit in proper fusion and irregularity of the horizontal gaze centers.
Strabismus has been known to occur in families, suggesting a multifactorial autosomal dominant pattern with incomplete penetrance. Genetically, the disease is passed down to each generation but does not produce symptoms in every individual who receives the set of aberrant genes. Additionally, environmental factors also influence development of exotropia.
A good review of risk factors and genetics in common comitant strabismus can be found here. [3, 12]
Epidemiology
Frequency
United States
Congenital exotropia is extremely rare in the United States. A 10 year retrospective study from Minnesota suggest occurs in less than 4 per 100,000 patients under 19 years old for a group of exotropia disorders including congenital exotropia. [16]
International
Exotropia of any kind had a worldwide prevalence of 1.23%. Congenital exotropia is a more rare form of exotropia with even lower prevalence. [17]
Mortality/Morbidity
There is a higher incidence of amblyopia in congenital exotropia than in other forms of exotropia. If uncorrected, persistent exotropia may lead to patients experiencing teasing and low self-esteem.
Race
No racial predispositions for congenital exotropia exist. Recent studies suggest a higher burden of the milder exotropia in Asian populations. [18]
Sex
No known sexual predilection exists.
Age
Congenital exotropia presents in infants younger than 6 months. Children who are born premature are at higher risk of developing strabismus; however, congenital exotropia is not known to occur at a higher rate in premature children.
