Exotropia

Introduction

Exotropia is a manifest divergent misalignment of the visual axes of the eyes. A latent outward deviation is called exophoria .

Intermittent exotropia (IXT; Fig. 11.7.1 , Video 11.7.1 ) is the most frequent cause of exotropia. It is a primary exotropia with an unknown cause. In some patients, IXT can be considered progressive; an exophoria may decompensate to an intermittent exotropia and finally to a constant exotropia. Based on whether diplopia is present during phases of manifest deviation, decompensated exophoria may be distinguished from IXT—in the latter, suppression prevents diplopia. Albeit uncommon, deterioration of IXT does occur, warranting regular observation of children with IXT to avoid loss of binocular functions and amblyopia.

Infantile exotropia, another primary exotropia, is very rare. It presents with constant exotropia within the first 6 months of life.

Exotropia also may be secondary to oculomotor palsy, Duane’s retraction syndrome, craniofacial disorders, internuclear ophthalmoplegia (INO), and other disorders. Occasionally exotropia develops after surgery for esotropia (consecutive exotropia) , or it may develop spontaneously in patients who had infantile esotropia. The distinction between primary and secondary exotropia is usually straightforward because of characteristic additional findings in cases of secondary exotropia. Sensory exotropia denotes an exotropic eye with typical adult onset as a result of severely reduced vision.

Epidemiology and Pathogenesis of Intermittent Exotropia

IXT makes up about 50% of exotropias in children; its incidence in the United States is 32.1 per 100,000 in persons under 18 years. Varying regionally in incidence, IXT is more common in Asian populations and possibly in women. Children with IXT may more frequently develop mental disorders, such as attention-deficit/hyperactivity disorder (ADHD) and adjustment disorder, including those who had a successful surgical alignment of the eyes. The distribution of refractive errors in patients with IXT is similar to that in the general population. Although no specific genes have been identified, exotropia seems to be hereditable, and inheritance is probably polygenetic.

Ocular Manifestations of Intermittent Exotropia

By far the most common type of exotropia, IXT typically presents between ages of 2 and 4 years with a gradual onset of exodeviation, more frequently noted when the child fixes on a distant target. Squinting (closing) of the deviating eye and eye rubbing in bright sunlight are noted frequently and may be the presenting complaint. Contracture of lateral recti in long-standing cases of constant exotropia, true overaction of oblique muscles, lateral gaze incomitance, and alphabet patterns may be associated. In many patients with IXT, normal retinal correspondence is present when their eyes are aligned and anomalous retinal correspondence (see Chapter 11.5 ) is present when the eyes deviate; these patients rarely complain of diplopia. When the deviation has been latent for a long time, these sensory adaptations may not develop, and patients experience diplopia when they have exotropia (decompensated exophoria). The angle of the deviation usually is stable until secondary contracture of the lateral recti ensues after long-standing manifest exotropia.