Strabismus: What's Happening?

Sensory adaptation to strabismus

The visual sensory system in children is able to adapt to pathological conditions (confusion and diplopia) through two mechanisms: suppression, abnormal correspondence of retinas. Their occurrence is associated with the plasticity of the developing visual system in children up to 6-8 years old. Adults with strabismus only rarely can ignore the second image and not experience diplopia.

Suppression occurs as a result of active suppression of the visual cortex of an image coming from one eye, with two open eyes. Stimuli for suppression are diplopia, confusion, defocused image with astigmatism or anisometry. Clinically, the suppression is subdivided as follows:

• central or peripheral. With central suppression, the image from the fovea of the deflected eye is suppressed to avoid confusion. Dipopia, on the other hand, is eliminated by means of peripheral suppression, in which the image is suppressed from the peripheral retina of the deflected eye;
• monocular or alternating. Suppression is monocular, if the image from the dominant eye dominates the image from the rejected (or ametronic) eye, the image of the latter is suppressed constantly. This type of suppression leads to the development of amblyopia. If the suppression alternates (ie, the image is alternately suppressed from one and the other eye), then amblyopia does not develop;
• mandatory or optional. Optional suppression occurs only when the eye position is not right. Mandatory suppression is constant, regardless of the position of the eyes.

Abnormal correspondence of the retina is a condition in which non-reciprocal retinal elements require a general subjective visual direction: the fovea of the fixing eye is paired with the unfaithful element of the rejected eye. Abnormal correspondence of the retina is a positive sensory adaptation to strabismus (as opposed to suppression), which supports a certain binocular vision with limited fusion in the presence of heterotrophy. Abnormal correspondence of the retina usually occurs with small-angle esotropy and rarely - with accommodative strabismus due to the inconsistency of the angle or at large angles due to separation of the retinal image. Abnormal correspondence of the retina is also rare in exotrophy due to a frequent periodic deviation. When strabismus occurs, the following occurs:

• The fovea of the mowing eye is suppressed to eliminate confusion;
• diplopia occurs because non-retrospective retinal elements receive the same image;
• to avoid diplopia, there is a phenomenon of peripheral suppression of the mowing eye or abnormal correspondence of the retina;
• the emergence of suppression leads to dysbinocular amblyopia.

The disadvantage of broken abnormal correspondence of the retina is that after surgical removal of strabismus the patient does not acquire normal correspondence of the retina, so the angle of strabismus can be restored when trying to restore binocular vision.

Motor adaptation to strabismus

It is expressed in changing the position of the head and occurs in those adults who do not include the phenomenon of suppression, or in children with potentially good binocular vision. With strabismus, the forced position of the head allows supporting binocular vision and eliminates diplopia. Rotation of the head is carried out towards the zone of action of the affected muscle, so the gaze is diverted in the opposite direction, as far as possible from the zone of the affected muscle (turning the head to the side in which the rotation of the eyeballs is impossible).

For horizontal deviation is characterized by a turn of the face. For example, with a paralysis of one of the horizontal muscles that turn the eyeballs to the left, turning the face to the left will compensate for the lack of movement in that direction.

Upright deviation is characterized by an ascending or lowering of the chin. With the weakness of one of the leftists, the chin rises, thus a relative lowering of the eyeballs occurs.

For torsion deflection, the inclination of the head to the right or left shoulder is characteristic. For example, with the paralysis of the intortor (the upper oblique muscle of the left eye), the left eye will be in a state of extrinsia. The inclination of the head to the right shoulder effectively compensates for the deviation of the left eye.

As a rule, the inclination of the head accompanies the vertical deviation. The slope towards the eye with hypotrophy is determined not by a vertical deviation, but by an accompanying (but less pronounced) torsional deviation.