Original article
Mechanism of Dynamic Visual Acuity Recovery With Vestibular Rehabilitation

https://doi.org/10.1016/j.apmr.2007.11.010Get rights and content

Abstract

Schubert MC, Migliaccio AA, Clendaniel RA, Allak A, Carey JP. Mechanism of dynamic visual acuity recovery with vestibular rehabilitation.

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, 42–66y) 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.

Section snippets

Methods

We studied 5 subjects (mean age, 54.4±8.9y; range, 42–66y) with vestibular hypofunction (4 with UVH, 1 with asymmetric BVH) before and after vestibular rehabilitation. Vestibular hypofunction was based on history of imbalance, nonpositional vertigo, physical examination showing a positive head thrust test result toward the affected ear, absence of a mass-enhancing lesion within the internal auditory canals or cerebellopontine angle, and abnormal DVA score. We also studied 4 control subjects

DVA score and aVOR gain

Trials of head thrust data that included blinks or in which the subject did not fix on the target with both eyes at the onset of head rotation were not included in the analysis. DVA scores for control subjects were in agreement with previously established age-matched healthy control values (table 1). The aVOR gains for passive head thrust testing and during the DVA testing were normal (table 2).Figure 1A illustrates a normal passive head thrust test in the horizontal canal for a 50-year-old

Discussion

Our data suggest that gaze stability exercises improve visual acuity during active head rotation via 2 primary mechanisms: an improvement in active aVOR gain and an increase in the number of compensatory saccades. In addition, our data suggest that gaze stability exercises reduce the perception of dizziness handicap experienced by subjects with unilateral vestibular hypofunction.

Previous studies suggest 2 possible explanations for how the gaze stability exercises improve aVOR gain during DVA

Conclusions

Our results suggest that DVA recovers as a result of improved active aVOR gain independent of peripheral vestibular recovery. In addition, we report that the number of compensatory saccades used per head rotation is variable and appears inversely correlated with passive aVOR gain. The compensatory saccades may be a useful gaze stability mechanism for some people. Together, these data suggest that vestibular rehabilitation has a mechanistic effect on recovery of gaze stability during active head

Acknowledgments

We thank Susan J. Herdman, PhD, for normative dynamic visual acuity data; Charles Rohde, PhD, for counseling with statistical analysis; and Paula R. Schubert, MSPT, and Jennifer Millar, MSPT, for editorial assistance.

References (43)

  • J. Bloomberg et al.

    Adaptive plasticity in the gaze stabilizing synergy of slow and saccadic eye movements

    Exp Brain Res

    (1991)
  • J.R. Tian et al.

    Vestibular catch-up saccades in labyrinthine deficiency

    Exp Brain Res

    (2000)
  • M.C. Schubert et al.

    Modification of compensatory saccades after aVOR gain recovery

    J Vestib Res

    (2006)
  • M.C. Schubert et al.

    Cervico-ocular reflex in normal subjects and patients with unilateral vestibular hypofunction

    Otol Neurotol

    (2004)
  • C.J. Bockisch et al.

    Enhanced smooth pursuit eye movements in patients with bilateral vestibular deficits

    Neuroreport

    (2004)
  • B. Fischer et al.

    Human express saccades: extremely short reaction times of goal directed eye movements

    Exp Brain Res

    (1984)
  • V.E. Das et al.

    Head perturbations during walking while viewing a head-fixed target

    Aviat Space Environ Med

    (1995)
  • G.E. Grossman et al.

    Frequency and velocity of rotational head perturbations during locomotion

    Exp Brain Res

    (1988)
  • S.J. Herdman et al.

    Computerized dynamic visual acuity test in the assessment of vestibular deficits

    Am J Otol

    (1998)
  • J.R. Tian et al.

    Dynamic visual acuity during passive and self-generated transient head rotation in normal and unilaterally vestibulopathic humans

    Exp Brain Res

    (2002)
  • M.C. Schubert et al.

    Dynamic visual acuity during passive head thrusts in canal planes

    J Assoc Res Otolaryngol

    (2006)

    • Cited by (0)

    Supported by the Foundation for Physical Therapy, American Physical Therapy Association and the National Institute on Deafness and Other Communication Disorders (grant nos. K23-007926, R03-DC007346, R01-DC005040).

    No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated.

    View full text
    Copyright © 2008 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.