20 - Balance, vestibular and oculomotor dysfunction

Summary

Introduction

Upright posture is inherently unstable in human beings: a heavy upper body must be balanced over a smaller lower body. The maintenance of upright balance requires that the center of mass be positioned within the base of support, either of which may be moving. Furthermore, in order to meet the demands of a constantly changing environment, body position and movement must be continuously monitored and updated with information received from the visual, somatosensory and vestibular systems. This multimodal sensory information is integrated within the central nervous system and, based on the perception of current demands on postural stability, an appropriate motor response is generated. The motor response must be accurately timed and scaled in order to prevent a fall. Failure in any one of the sensory or motor systems results in impaired ability to control posture and may result in a fall. The effect of sensory or motor system loss on maintaining balance varies with the degree of challenge to stability. For example, the balance challenge to an individual is very different when standing still compared to standing on a bus that suddenly lurches. This chapter will focus on:

1. vestibular contributions to postural stability;

2. the effect of peripheral vestibular loss on balance and postural control;

3. the effect of eye movements on balance;

4. the role of vestibular rehabilitation (VR) in the remediation of imbalance and gaze instability.