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 vestibu lar ocular reflex assessment. Study Design: The study was a comparison with age-matched controls. Setting: The study was performed in a clin ical neurophysiology laboratory. Patients: Ten patients with acute uni lateral vestibular nerve section and 9 patients in the chronic stage o f 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 expo sed to discrete, raised cosine velocity (60 degrees/s peak) rotations, for random displacements less than or equal to 180 degrees rightward and leftward. They responded by rotating themselves back to the starti ng position with a joystick control. Horizontal canals were tested wit h 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 appro ximately 45 degrees to the left or right. Main Outcome Measures: These were accuracy and symmetry of responses. Results: Normal responses we re approximately accurate returns to start. Nine patients with acute n erve section were hypometric (undershooting start) when displaced towa rd 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 respon ses for horizontal canal testing. Patients with posterior canal pluggi ng were hypometric specifically toward the plugged canal. Conclusions: The method reliably identifies acute and chronic dysfunction of verti cal canals and acute dysfunction of horizontal canals. Dysfunction of a single canal can be specified.