Evaluating 3D semicircular canal function by perception of rotation.

Objective: We aimed to develop a clinical test of 3D canal dysfunction by perceptual matching of motion stimuli as an alternative to vestibular ocular reflex assessment.

Study Design: The study was a comparison with age-matched controls.

Setting: The study was performed in a clinical neurophysiology laboratory.

Patients: Ten patients with acute unilateral vestibular nerve section and 9 patients in the chronic stage of recovery, 2 acute-stage and 2 chronic-stage patients with posterior canal plugging, and 35 healthy individuals were studied.

Interventions: Seated on a motorized rotating chair in darkness, subjects were exposed to discrete, raised cosine velocity (60 degrees/s peak) rotations, for random displacements < or = 180 degrees rightward and leftward. They responded by rotating themselves back to the starting position with a joystick control. Horizontal canals were tested with head upright, ipsilateral versus contralateral vertical canal pairs were tested with the head down, face horizontal and co-planar anterior-posterior canal pairs were tested with the head down and turned approximately 45 degrees to the left or right.

Main Outcome Measures: These were accuracy and symmetry of responses.

Results: Normal responses were approximately accurate returns to start. Nine patients with acute nerve section were hypometric (undershooting start) when displaced toward the lesion but normometric to the intact side. Eight chronic-stage nerve section patients with chronic dysfunction were hypometric to the lesion for vertical canal stimuli, but one third showed normal responses for horizontal canal testing. Patients with posterior canal plugging were hypometric specifically toward the plugged canal.

Conclusions: The method reliably identifies acute and chronic dysfunction of vertical canals and acute dysfunction of horizontal canals. Dysfunction of a single canal can be specified.