Exotropia is a type of strabismus (eye misalignment), where one eye turns, or deviates, outward (away from the nose). The deviation may be constant or intermittent, and the deviating eye may always be one eye or may alternate between the two eyes. The deviation or eye turn may occur while fixating (looking at) distance objects, near objects, or both. Exotropia is also often called wall-eyed.
Infantile exotropia is evident shortly after birth and often before 6 months of age. Infants don't have great eye movement control in the first few weeks of life, but by 6 months the child should have full control of eye movements. Infantile tropia (exo- or esotropia) can be very debilitating to the development of normal binocular vision, as the child starts life unable to develop normal visual skills, such as stereopsis (depth perception).
Intermittent exotropia is a subset of exotropia that is present only once and a while. The patient often can control eye positioning most of the day, but an eye may turn outward with a stressful condition or extended near work.
Alternating exotropia refers to how a patient fixates. A patient with a constant exotropia fixates with one eye, all the time. This would be called a unilateral (right or left) exotropia. Patients with an alternating fixation pattern switch fixation between each eye.
Mechanical exotropia is often due to fibrosis (or scar tissue) that prevents the eye from moving inward. Some conditions, such as overactive thyroid, can leave deposits in muscles and cause an abnormal tightness for an eye muscle to move. Damage from broken bones around the eye (the area called the orbit) may also limit eye movement.
This often occurs in patients older than 5 years of age that have severely lost vision in one eye. The brain is unable to fuse the images from the normal eye and the eye that has lost vision, so the eye drifts outwards.
Microtropias are small deviations of the eye that can be quite tricky to see. Inward microtropia (microesotropia) is much more common than microexotropia.
The distinguishing sign of exotropia is one or either eye wandering outward. Symptoms may be mild or severe. If suppression of the deviating eye occurs, the patient can have diminished binocular vision and diminished stereopsis. Patients may also experience diplopia (double-vision). Asthenopia (eye fatigue) can also occur with reading.
Causes of exotropia are mostly unknown. Children with a family history of the disorder are more likely to get them. They are also common in children who have other systemic (chromosomal or neurologic) disorders.