Mechanism of dynamic visual acuity recovery with vestibular rehabilitation

Objective: To determine why dynamic visual acuity (DV improves after vestibular rehabilitation in people with vestibular hypofunction. Design: Combined descriptive and intervention study. Setting: Outpatient department in an academic medical institution. Participants: Five patients (age, 42-66y) and 4 age-matched controls (age. 39-67y) were studied. Patients had vestibular hypofunction (mean duration, 177 +/- 188d) identified by clinical (positive head thrust test, abnormal DVA), physiologic (reduced angular vestibulo-ocular reflex [aVOR] gain during passive head thrust testing), and imaging examinations (absence of tumor in the internal auditory canals or cerebellopontine angle). Intervention: Vestibular rehabilitation focused on gaze and gait stabilization (mean, 5.0 +/- 1.4 visits; mean, 66 +/- 24d). The control group did not receive any intervention. Main Outcome Measures: aVOR gain (eye velocity/head velocity) during DVA testing (active head rotation) and horizontal head thrust testing (passive head rotation) to control for spontaneous recovery. Results: For all patients, DVA improved (mean, 51% +/- 25%; range, 21%-81%). aVOR gain during the active DVA test increased in each of the patients (mean range, 0.7 +/- 0.2 to 0.9 +/- 0.2 [35%]). aVOR gain during passive head thrust did not improve in 3 patients and improved only partially in the other 2. For control subjects, aVOR gain during DVA was near 1. Conclusions: Our data suggest that vestibular rehabilitation increases aVOR gain during active head rotation independent of peripheral aVOR gain recovery.