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) distant objects, near objects, or both. Exotropia is sometimes called wall-eyed (however this is technically reserved for a rare form of bilateral strabismus called internuclear ophthalmoplegia). Exotropia is a form of strabismus where an eye deviates outward. It is the opposite of esotropia and occurs intermittently or constantly. Patients with moderate or severe exophoria are more likely to develop intermittent exotropia.
Infantile exotropia is evident shortly after birth and often before 6 months of age. Infants do not 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 affect the development of normal binocular vision, as the child may not develop normal visual skills, such as stereopsis (depth perception) or fusion, or may develop cortical suppression to alleviate double vision.
Intermittent exotropia is a subset of exotropia that occurs 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, such as extended near work. Intermittent exotropia is often associated with convergence insufficiency, a condition where the patient has adequate control of eye position when viewing at a distance, but a high exophoria (outward eye position) at near that may fatigue over time to become an exotropia.
Alternating exotropia refers to how a patient fixates. A patient with a constant exotropia of one eye fixates with the same eye all the time. This would be called unilateral (right or left) exotropia. Patients with an alternating fixation pattern switch fixation between each eye. Alternative tropia patterns often have decent vision between each eye due to the ability to switch fixation from one eye to the other.
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 severe discrepancy of 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. Microtropic patients will often have a significant improvement with vision therapy treatment as they are the patients most likely to recover full in-depth stereopsis and thus full binocular function.
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 poor or no stereopsis. Patients may also experience diplopia (double vision) or asthenopia (eye fatigue).
Intermittent exotropia that develops before a child is school-aged and can be rather difficult to detect. Parents may be unable to describe accurately the abnormality that they see in a child’s eye, and will often say that the eye looks ‘funny’ or ‘glassy’. The ocular deviation may initially present only from a distance, when the child is tired or sick, or when he or she is daydreaming. Parents may notice the misalignment, ask the child to look at them, and the eyes suddenly are perfectly straight. Because the eyes are only intermittently deviated, the incidence of amblyopia in this condition is quite low, and the children tend to develop good binocularity and stereoscopic vision. The issue may be more problematic once a child's schoolwork requires more intense focus. Exotropia associated with convergence insufficiency is more common in older school-aged children as well as adults. This type of intermittent exotropia is often associated with complaints of eye strain, headache, and double vision with extended near work.
Diplopia specifically is often not reported by children if they have a constant exotropia. Unless suppression develops, a patient will likely notice double vision when an eye starts to wander. Patients experiencing double vision will often begin to close one eye to be able to continue the task they are performing. Detection of this symptom alone is an indication for a referral to a developmental optometrist.
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. The following may be causes of exotropia:
Both esotropia and exotropia may be congenital (present at birth) or acquired (developed later, during childhood). Exotropia likely occurs from an imbalance in signaling issue between the brain and the eye muscles responsible for eye movement. Approximately 30 percent of children with strabismus have a family member with the condition. When no family history, illness, or condition can be identified, doctors aren’t sure what causes strabismus like exotropia to develop. Regardless of the cause, the workup for a patient with suspected exotropia should include an eye health examination as well as an evaluation of binocular vision.
A diagnosis is usually made based on family history and thorough and comprehensive vision testing. A developmental optometrist — and eye doctor who specializes in eye issues — are best equipped to diagnose this disorder. They’ll ask you about symptoms, family history, and other health conditions to help them make a diagnosis.
Your doctor will also conduct a number of vision tests. These can include:
-Reading letters from an eye chart if your child is old enough to read -Placing a series of lenses in front of the eyes to see how they refract light -Tests that look at how the eyes focus -Testing eye alignment with prism lenses -Using dilating eye drops to help widen the pupils of the eyes and allow a doctor to examine their internal structure and health of the eyes
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