Title

Mechanisms of gaze stability in persons with vestibular hypofunction

Date of Award

2001

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physical Therapy

First Committee Member

Neil I. Spielholz, Committee Chair

Abstract

One of the primary functions of the vestibular system is to keep the eyes fixed on a target (gaze stability) during a rapid head movement. When an individual with a healthy vestibular system moves his head, the vestibular system moves the eyes with an equal velocity in the opposite direction to ensure clear vision during the head motion. When an individual with a damaged vestibular system moves his head, the eyes move in the same direction as the head resulting in poor vision during head motion. Although various compensatory mechanisms that can be used to assist gaze stability during head motion have been studied in subjects with loss of vestibular function, no study has attempted to measure all of the compensatory mechanisms in individual subjects. The purpose of this research was to identify the various compensatory mechanisms that persons with vestibular hypofunction use to assist gaze stability and determine how subjects differ in their use of these mechanisms. Subjects and methods. Four persons with vestibular hypofunction (2 with unilateral loss, 2 with bilateral loss) and four persons with healthy vestibular function were studied. Eye movements were recorded with the scleral search coil system during head motion (predictable and unpredictable) and when the trunk was moving beneath a stabilized head. Results. All subjects with vestibular hypofunction used saccades and slow eye motions to assist in the stabilization of a target on the retina. One of the subjects with unilateral vestibular hypofunction also used input from the neck to generate an eye motion while a second subject with unilateral vestibular hypofunction was shown to use central vestibular adaptation to assist gaze stability. A central preprogramming mechanism to assist gaze stability was found in the other subject with unilateral vestibular hypofunction and in one of the subjects with bilateral vestibular hypofunction. None of the subjects with healthy vestibular function were found to use any mechanism other than the vestibulo-ocular reflex to stabilize gaze. Conclusions. Subjects with vestibular hypofunction appear to recruit different mechanisms to maintain gaze stability during head motion. Implications are made for exercise approaches that might supplement these compensatory mechanisms.

Keywords

Biology, Neuroscience; Health Sciences, Rehabilitation and Therapy

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3032386