In Part 1 of Ocular Discriminative Movement Dr. Wachs paves the way for his elegant description of what we mean by the term fusion: the combination of two visual images, right and left, into a single image that differs from each of the individual images but contains all of their elements. It is therefore safe to say that anything that interferes with the combination of the two visual images contributes is con-fusion. It may not be obvious cosmetically, but the child in this photo has a constant left exotropia. Just as epicanthus simulates esotropia, it can cosmetically mask exotropia, which in this child’s case measures approximately 20 prism diopters. He suffered a lacerating injury of the left eye, and while he retains 20/20 unaided visual acuity in both eyes, there is no longer a common visual direction between them. This con-fusion has resulted in suppression of the left eye and his case our job is create better monocularity so that, at the very least, we help his brain utilize more central rather than peripheral processing of the left eye. In Part 1 we talked about the significance of monocularity and ocular calisthenics, and you can see that readily in this young child’s case. When we cover his right eye he is able look straight ahead with the left eye, and his ability to localize where an object is in space with the left eye is good as long as the object is directly in front of the left eye. Although he appears to have good range of physical motion of the left eye inward when looking toward the right field, his spatial projection has shifted and considerable past pointing is evident. This means that there is a mismatch between the innervation to the muscle, and muscle output, as originally noted by Von Graefe regarding monocular past pointing as a change in egocentric localization in paralytic strabismus. I’ll put up several pictures to illustrate this.
The top photo shows the left eye fixating in primary gaze when the right eye is fogged with a translucent occluder. The second photo shows the child’s ability to look rightward with the left eye. We instructed him to keep his head straight while looking rightward with the left eye. Holding a silver Wolff Wand in the right field, we asked him to use the index finger of his right hand to localize or point to where he thought the silver ball was located. The third photo shows him past-pointing considerably beyond the location of the ball. The fourth photo shows that he has no problem localizing where the ball actually is when we allow him to rotate his head to the right, thereby allowing the left eye to look at it directly along its primary or straight ahead visual axis.
Going back to Part 1, there are a number of procedures we’ll need to do in preparing the left eye to share more common visual direction with the right eye. We’ll move from working directly in front of the left eye, for which his localization skills are accurate even for precision tasks such as pointer-in-straw, to judgements when the left eye is adducting just a few degrees off the visual midline, progressing toward looking inward to the nose. While one could say we’re doing ocular calisthenics and stretching, we are simultaneously engaging the patient in cognitive acts of visual thinking and visually guided movement. It supports the notion that a good deal of vision therapy is analogous to physical therapy, but with more emphasis on the cognitive components.