Practical usefulness of anomalous binocular vision for the strabismic patient

Conclusions

Considering that many features of anomalous binocular vision resemble those of normal binocular vision, we believe that it is possible to state that subjective adaptation to squint is an exaggeration of physiological phenomena. In other words, both sensory sequelae (suppression and ARC), and sensory-motor sequelae (AFM) are not too different from NRC and NFM.

In the old days ARC was thought to be nothing more than an abortive attempt of the strabismic patient towards binocularity (8). We have shown that ARC and AFM interact in maintaining an anomalous binocular vision. ARC, if extended all over the binocular visual field allows the patient an anomalous type of sensory fusion and makes it possible to enjoy binocular single vision in a large area of space. This type of vision is made rather stable by AFM. Their finality is to maintain the small-angle deviation. They oppose, when sufficiently strong, any change in the sense of an increase of the angle - which would cause supression and loss of binocularity. On the other hand they oppose as well a decrease of the angle - as tried with therapy. This point is of practical importance. It is well known that surgery for small-angle deviation is very ineffective. The same amount of surgery in large-angle strabismus causes a much greater effect. The reason is that in small-angle strabismus AFM are most effective.

It is possible — at least in selected cases — to normalize retinal correspondence and to eliminate AFM. Surgery and prismatic temporization therapy (1) are able to disrupt an ARC and reconstitute a NRC, and the same methods may weaken AFM.

The issue is that once correspondence is normalized and AFM are eliminated, normal binocular vision is not yet re-established, for the patient lacks NFM. The latter entity is almost impossible to achieve, particularly in congenital esotropia. The patient with congenital esotropia has never experienced normal motor fusion in his life. It is therefore very unlikely that, once the eyes are straightened, he will have his motor fusion functioning. Some late-onset strabismus cases who previously enjoyed normal fusion may re-acquire it if the treatment is started not too long after the loss of ocular augment. Motor fusion, as with many binocular functions, needs to be innately present and also needs to be constantly used, like a pianist requires both talent and exercise (as Dr. Burian used to say).

For the above mentioned reasons, a sensory treatment of a strabismic patient is often fruitless and sometimes even dangerous. In fact, a normalization of correspondence without NFM, may cause diplopia, if the eyes are not perfectly aligned; this is particularly likely after 10 year of age.

In conclusion, anomalous binocular vision has to be considered as a quite positive end-result in the treatment of strabismus. If the deviation is not cosmetically disturbing and amblyopia has been prevented or treated, one should best leave the patient alone. On one hand this patient has a certain amount of binocular cooperation. On the other hand the anomalous binocularity itself prevents any normalization of the sensory status.