Adaptive esotropia

Adaptive esotropia

This is the most common type of esotropia and is closely connected with hyperopia.It appears in ages from 6 months to 5 years old, with a more typical appearance at the age of 2. Initially it may be intermittent, but it quickly becomes permanent.

Most children prefer to use only one eye, and thus the risk of amblyopia is high for the deviating eye.If adaptive esotropia occurs during the period the child is sick or after a fall, many parents think the appearance of strabismus is caused from the disease or injury. This of course has no scientific basis and this simultaneous occurrence is just a coincidence.

Pathophysiological mechanism

The human eye, as we have already said, is "tuned" to look far away. When a normal person is focused on a nearby object, the ciliary muscle presses the lens and increases its focal power. This process is called adaptation.

To people with hyperopia, the eye is forced to use also the same mechanism to focus on distant objects, while for nearby objects the effort becomes even greater.The adaptation is always accompanied by a certain amount of convergence, a shift of both eyes inwardly (nasally). The greater the adaptation the greater the convergence. So if hyperopia is quite high, it is possible that the convergence accompanying the intense adaptation will lead to esotropia.

The correction of hyperopia using suitable glasses relieves the eyes from the extra load, and thus the adjustment is not so great for the attendant convergence to result in esotropia. Therefore, the use of glasses leads to alignment of the eyes, but only when the child wears them.

Adaptive esotropia is frequently found in members of the same family, as the great hyperopia that causes it is a "construction type" and therefore hereditary.

The treatment of adaptive esotropia

The first step is to calculate hyperopia and any co-existing astigmatism and then administer the appropriate glasses. Amblyopia must also be addressed if the child starts showing it.

From the day the child starts wearing glasses, esotropia will gradually start to decline, with the maximal effect achieved within a month.

In most children we have full elimination of adaptive esotropia. In others though, strabismus is still evident and they must undergo surgery to correct the remaining esotropia. Parents of such children ask "why operate on the rest and not the whole amount of esotropia, so the child’s eyes are aligned, even if not wearing glasses?" The answer is that the cause of adaptive esotropia is hyperopia, a refractive error, and not a problem of the muscles that we can operate on. Furthermore, full correction has the risk of transitioning to exotropia.

The child needs to wear its glasses, for as long as hyperopia remains that high, so that it causes increased convergence and esotropia. For most children this might mean for the rest of their lives. Generally, the course of hyperopia is: increase until the age of 6 and then decrease until the end of puberty. Very few children are lucky enough for hyperopia to completely vanish in adulthood.

Adaptive esotropia only on close up vision

Some children with hyperopia do not show esotropia on their distance vision but instead, only when they focus on a nearby object. In these cases, it is more difficult to identify esotropia because the object itself may be very close up (eg a book) and hide the child's face, preventing the parents from distinguishing the problem. Such situations are often recognized when feeding and the child lifts his head so it is easier for the parents to see his eyes.

The treatment of this form of esotropia is the use of bifocal glasses, which are glasses whose lenses contain a stronger lower part for nearby vision. Of course, if the kids look nearby through the top part with the lesser degrees, for long, strabismus can instantly reappear. Generally, children don’t have a problem with the use of bifocal glasses and even seem to get used to them much more easily than older, adult patients.