After a period of welcome “shut down” or cerebellar clamp, a patient recovering from an acute Vestibular Neuritis (VN) has to decide when they are ready to begin the process of recalibrating the Vestibular-Ocular Reflex (VOR). We all benefit from a constant calibration process between our inner ears and our eyes. The goal of this calibration is to assure that the brain sends the correct signal to the eyes in response to movement-generated signals it receives from the inner ears.
An example of this calibration process is familiar to most everyone who has experienced a few days of nausea and visual disorientation after receiving a new eyeglass prescription. What is happening there is that the change in magnification from the new glasses requires a change in the amount of eye movement triggered by the signals from the inner ears. Nothing has changed in the ears, but the brain needs to recalibrate how much signal it sends to the eyes.
In the case of acute VN, there is typically a huge reduction in the signal sent to the eyes, even though one ear is still healthy and registering movement normally. This reduction is referred to as a decrease in gain of the VOR, and is measurable on rotational chair tests. From the patient’s perspective, they can’t keep their eye focused on objects when their head is moving.
As mentioned last week, nausea is a common consequence of pushing the vestibular system beyond its capabilities (think merry go rounds and roller coasters). Unfortunately, there is often a knee jerk reaction to treat these symptoms with meclizine (antivert). While meclizine may take the edge off the nausea, it inhibits natural recovery (or “wake up” phase) and prolongs the symptoms of visual blurring and instability. In this situation, I often make the analogy of a cast on a broken ankle. In the early stages, the cast protects the ankle, but to restore function of that ankle you have to eventually take off the cast and work through the stiffness and soreness.
Given the opportunity, the healthy brain will compensate and restore VOR function and visual stability to maximal (if not necessarily normal) levels. The opportunity it needs involves lack of sedating medications like meclizine, and activities that require visual focus associated with head movement. Some people can recover through normal day-to-day activities, while others benefit from working with a vestibular therapist.
We wrap up this series next week with a discussion of variables in the compensation process.
Photo courtesy of https://theconcussionblog.com/tag/recovery/
Cheesy George Michael photo courtesy of https://magnum1971mixes.blogspot.com/2014/03/wham-wake-me-up-before-you-go-1984.html