We laid out a framework for visual centers of gravity in Part 1. Certainly head injury can result in significant alterations of this framework, where shearing forces can disrupt the “GPS” provided by the tight coupling between visual and vestibular systems guiding body movement in vectors of space. It is not surprising at all to find alterations in the semicircular canals, even in mTBI/concussion. Otoliths, the crystals in the semicircular canals that helps sense gravitational movement, can be dislodged so that the fluid the bubble of the level in any or all of the planes of rotation can mis-calibrating.
Of course, mis-calibration in any of the planes of the extraocular muscles is a well-known outcome of mTBI, and damage due to trauma at any level – either innervationally or structurally can result in altered calibration of the primary, secondary or tertiary actions of the EOMs. Alterations in calibration can occur developmentally, in the absence of known trauma. Clinical experience also provides evidence that many children who skipped the reciprocal interweaving of cross-patterned crawling in development have various degrees of binocular dys-integration.
Perhaps the most common postural skews secondary to adaptive changes in visual centers of gravity occur in non-comitant strabismus. One of the more common forms of non-comitancy is “V” pattern exotropia, in which the outward drift of one eye relative to the other eye is exaggerated in upward gaze. Here is an example of a “V” pattern that occurs in overaction of the right inferior oblique muscle.
What most ophthalmologic sources don’t show is that non-comitant strabismus is the ultimate example of a head-to-toe adaptive postural skew. Here is a patient I saw in the office yesterday. What do you notice?
That’s right. She fuses in primary gaze, but has a 4+ OAIO of the right eye on gaze left, just like the slide above. And just like the slide above, she has a “V” pattern exotropia when looking straight upward. So obviously every time she looks toward her left side, or looks upward to any significant degree, she experiences double vision. Think her center of gravity is altered? Absolutely. What is her postural adaptation? She adopts a skew where she rotates her head to the left, minimizing the need to gaze leftward, and elevates her chin, minimizing the need to look upward. Try it. You’ll feel your shoulders rotating so that your right shoulder dips downward. If it’s hard for you to feel this, exaggerate the amount of head rotation to the left and chin elevation, and at some point I guarantee you’ll feel it, particularly when you’re seated.
Aside from vision therapy procedures to spread comitancy, there are options for yoked prism. Either bases up in both eyes, or bases left in both eyes should give the patient some immediate relief. But bear in mind that this is a head-to-toe center of gravity issue. So in the process of therapy we will work with the brain to recalibrate at the level of all the body’s x/y/z balance and movement systems: from the pivot points of the eyes, to the pivot points of the head, to the gain in the VOR, and translating to the sternocleidomastoids of the neck and shoulder to the hips and ultimately to the motor end plates in the feet.
Viewed in this light, a trampoline is an essential tool in helping the brain re-write equations that recalibrate binocular integration from head to toe. Pointer-in-straw is valuable x/y/z work for eye-hand, but trampoline physics is superb x/y/z work for eye-body.