Mechanism of dynamic visual acuity recovery with vestibular rehabilitation

Abstract

Objective: To determine why dynamic visual acuity (DVA) 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, 42-66 y) and 4 age-matched controls (age, 39-67 y) were studied. Patients had vestibular hypofunction (mean duration, 177+/-188 d) 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+/-24 d). 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.

Fig 1

aVOR gain during passive horizontal head thrust testing in a healthy control subject and subject with left UVH. Left and right refer to direction of passive horizontal head thrust rotation. (A) Data from both eyes in a subject with normal VOR function. (B) Data from left eye only in a subject with left UVH. Head and/or eye velocity plots have been inverted for ease of comparison. Note that the quick phases in the bottom left panel are in the same direction as the slow-phase eye velocity, illustrating the compensatory saccades.

Fig 2

(A) Patients with UVH and partial recovery; (B) patients with UVHc; and (C) patients with BVH. Improvement of aVOR gain during DVA testing. Eye velocity plots have been inverted for ease of comparison. Eye velocities are from left eye only. For head rotation in the contralesional direction, compensatory saccades occur with much less frequency, suggesting that compensatory saccades recruitment is dependent on subjects’ intent for gaze stability. NOTE. The compensatory saccades (CS) ratio is the number of compensatory saccades/total number of head rotations.