You may be familiar with the concept of post-rotary nystagmus, in which spinning around in circles makes you dizzy from sloshing up your semicircular canals, and sets off a characteristic oscillating motion of your eyes when you stop spinning. Here is a real-time recording of what the eyes of a normal child are doing during rotation and then immediately post-rotation, as projected onto a video monitor.
We know that visual fixation under normal viewing conditions serves to dampen post-rotary nystagmus and stabilize balance through visual-vestibular interaction. Frenzel goggles are high power convex lenses that serve to magnify the subjects’ eyes making the post rotary nystagmus more visible to the examiner, and also to blur the visual field significantly to impair the dampening of post-rotary nystagmus. Here is a video of a young adult’s eyes during post-rotary nystagmus, wearing Frenzel goggles.
In a search of the literature I was unable to find any publications on the effect of concussion on post-rotary nystagmus. By way of this post I am theorizing that concussion impairs post-rotary nystagmus in a way similar to Frenzel goggles, rendering the individual as “being in a fog”, as occurs with the high plus lenses. Specifically, impaired visual-vestibular interaction should inhibit the ability of the visual system to dampen post-rotary nystagmus. This would increase the decay time of pos-rotary nystagmus, and would be measurable objectively.
One of the holy grails of concussion testing is an objective measure that does not require responses on the part of the individual suspected of being concussed, or interpretation of the individual’s responses. I am proposing that post-rotary nystagmus can be measured objectively through a sensor, either in glasses or though a fixation target, and that a baseline measure can be established of the duration of post-rotary nystagmus (PRN).
When testing an athlete, I am proposing that concussion prolongs PRN time, and impedes stabilization of gaze than dampens PRN. This has great potential to complement other tests used for both remove from play as well as return to play, or return to learn. It is entirely independent of intellect, and requires limited if any instructional set, or interpretation of verbal responses. Baseline data can be established for post-rotary nystagmus done in the standing or vertical position, as opposed to sitting in a chair, which would be more pertinent for athletes. For return to learn or driving, being seated in a chair may be more pertinent.