Learning More About Exotropia Surgery
Exotropia typically develops in a progressive course. First, the eyes rarely turn outwards, usually when the patient is tired or sick. As you know, when strabismus occurs with fatigue, or only under testing conditions, this is an exophoria.
Next, the eyes start to spontaneously deviate outwards, only to straighten out moments later. This is an intermittent exotropia. When an intermittent exotropia is present, it means that the brain is unable to maintain depth perception all of the time, but maintains the capability some of the time. At this point, depth perception is still present but is at risk of being diminished or lost. Finally, as the intermittent exotropia becomes less well controlled, the eyes turn outwards more frequently – once the eyes are constantly turned outwards, this is an exotropia.
It is preferable to repair an intermittent exotropia because we know that the binocular cortical cells are still functioning. Once the eyes are constantly exotropic, the binocular cells may be damaged to the point that binocularity has been lost – in this case, there will be no stimulus for the eyes to remain straight after surgery. Thus, it is best to operate on an intermittent exotropia that is becoming more frequent. The decision to operate is based on thefrequency of the exo-deviation, not the size of the turn. For example, a small constant exotropia can be operated on at any time, but a large intermittent exotropia that occurs infrequently is probably not ready for surgery.
A few more things about exotropia: First, patients who are myopic (near-sighted) and have an exotropia should wear their glasses all of the time, as this may help to limit the frequency of the exotropia. Second, there is a type of exotropia where eye exercises (orthoptics) can help – if the exotropia is largest when looking at something up close. In this situation, called convergence insufficiency, orthoptic exercises can be effective if performed properly. Convergence insufficiency is the only type of strabismus that has been demonstrated to respond to orthoptic (“vision”) therapy.