In rotary chair testing, which metrics are derived to assess bilateral vestibular function across frequencies?

• A. VOR latency, gain, and duration
• B. VOR gain, phase, and symmetry across frequencies
• C. Eye velocity, nystagmus amplitude, and latency
• D. Head impulse velocity, smooth pursuit gain, and drift

Answer: (B)

Rotary chair testing assesses how the vestibulo-ocular reflex responds to controlled head rotations across a range of frequencies, revealing how well both vestibular systems work together. The best set of metrics to capture bilateral function across frequencies are VOR gain, phase, and symmetry across frequencies.

VOR gain is the eye velocity divided by head velocity; it shows how effectively the eyes counter head movement. When the system is healthy, gain stays close to 1 across frequencies, meaning the eyes compensate almost perfectly. Phase looks at the timing between head and eye movements. A phase near zero means the eye movement is in sync with the head movement, stabilizing the image; deviations indicate delays or advances in the response that can point to vestibular dysfunction at certain frequencies. Symmetry across frequencies examines how responses compare in opposite directions (left vs right rotation) across the frequency spectrum. High symmetry indicates balanced bilateral function, while reduced symmetry suggests bilateral or asymmetric impairment.

Other metrics like latency or raw eye velocity without considering the frequency-dependent relationship, or measures from other tests like head impulse velocity or pursuit, don’t specifically quantify bilateral vestibular function across the full frequency range in the way that gain, phase, and symmetry do.