General EYE ADVICE

Eye Coordination (Alignment) Defects - ESOTROPIA

Good control of eye movements and teaming of the eyes, also requires a healthy neuro-muscular system. An imbalance of the ocular muscles can lead to an eye turn (strabismus) in the presence of a weak neuro-muscular system. Whether or not strabismus results depends on the magnitude of the genetic defect, the extent of lack of the necessary nutrition and on other factors such as lack of visual experience etc.

It would be ideal to have all newborns examined by an eyecare practitioner at three months of age. This is mainly so as to detect those children who are significantly long-sighted.

These infants should be followed up more carefully at regular intervals, in case an eye-muscle imbalance develops which may lead to esotropia (inward turn of one of the eyes). Should there be any sign of esotropia in the presence of long-sightedness, corrective lenses should be prescribed as soon as possible.

It is believed by certain workers in the field (and the author agrees with this view), that significant amounts of long-sightedness can lead to esotropia even within the first few months of life. Without corrective lenses, long-sighted infants must constantly focus more than the usual amount in order to see clearly. As accommodation (focusing) is normally accompanied by convergence (aiming of the eyes at a closer distance) in a reflex manner, an excessive amount of focussing will lead to excessive convergence or crossing of the eyes.

There are several factors that determine whether the eyes will remain "crossed" or become realigned. These are mainly related to the extent to which the eyes are crossed and to the ability of the infant to fuse the images from both eyes into one single image derived from both eyes.

The extent to which the eyes are "crossed" is mainly determined by the magnitude of the long-sightedness and whether there is a genetic tendency for an excessive amount of convergence of the eyes in response to focussing. The anatomical starting alignment of the eyes at birth would also play a role.

The ability to fuse is governed by several factors. One such factor is whether there is clear and equal vision in both eyes. The most common cause of unequal vision and a potent contributing factor to esotropia, is anisometropia. An example of this condition is when one eye is significantly more long-sighted than the other. Pathology such as cataract or retinal damage can also be the cause of reduced or unequal vision.

The alertness of the infant that enables it to sense the lack of single and cohesive vision, and the strength of the neuro-muscular system in opposing the excessive reflex convergence due to accommodation, are also important in instigating fusion. Some workers believe that the inherent ability to fuse two superimposed images, which is present in most infants, may be somewhat lacking in some infants. The underlying cause would probably be of a genetic nature.

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