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Description Of Exotropia
The usual description of exotropia is that one (or both) eye deviates in an outward direction (i.e. away from the nose) when looking at an object. Exotropia is defined as a type of strabismus (or tropia), which simply means that the eye deviates away from an object that the subject is attempting to look at. Strabismus is known by a host of other names including crossed eyes; wall-eyes; deviating eye; eye turns and wandering eyes.
Extropia can occur when the subject is fixated on a distant object or when they are focused on something close at hand, or under both circumstances. The condition is usually intermittent (intermittent exotropia) but may occur all of the time (constant exotropia). Should the condition affect both eyes, causing them both to turn outwards, then the correct description of exotropia is exophoria, otherwise known as convergence insufficiency. In patients suffering from the condition, a force is exerted on the affected eye by the lateral rectus muscle, which causes it to move in an outward (away from the nose) direction.
It has been estimated that roughly one percent of the general population will be affected by exotropia. There seems not to be any gender related component to the disease with as many male as female sufferers. Usually, intermittent exotropia is preceded by a short phase of exophoria and it represents somewhere between 50 and 90% of cases.
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Symptoms Of Exotropia
Children suffering from exotropia often close an eye when outside; sufferers look as if their eye is “turned out” – the human eye is very quick to see where another person’s eye is looking! The description of exotropia is that the deviation of the eye occurs whilst looking at distant objects, objects that are close or both. Exotropia is mainly an intermittent condition and is the most common type of strabismus to occur in childhood. When the problem is associated with fixating on distant objects, the problem is largely cosmetic, but the child may get accused of not paying attention or daydreaming and can occur during periods of fatigue or inattention. In cases where the problem is with looking at objects close to the patient, symptoms will include headaches; diplopia (double vision), difficulty to concentrate during reading; eyestrain and blurred vision.
The precise reasons underlying exotropia remain unclear, but most experts seem to accept that the brain has trouble influencing control over the eye. There is some evidence that the condition has a genetic component, running in families. The age of the sufferer at onset varies from 6 months and 4 years, but so long as the eyes are straight for some of the time, the brain will develop at least some sort of normal functioning (stereoscopic depth perception).
The condition may stem from head or eye injuries, deformities or nerve problems and in the adult population, can stem from diabetes, multiple sclerosis, brainstem aneurysms, thyroid conditions, myasthenia gravis, and circulatory problems.
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Treatment Of The Disease
If exotropia is present more than half of the time, or is clearly increasing, or the child is losing binocular vision or suffers extensive exotropia when looking at near objects, then eye muscle surgery can be considered to treat the condition. In milder cases, eye patches or glasses may be required to “train” the eye with the weaker muscle. Whilst mild exotropia can spontaneously improve, it is unusual and some type of intervention is often required.