Influence of pathologic and simulated visual dysfunctions on the postural system.

Visual control has an influence on postural stability. Whilst vestibular, somatosensoric and cerebellar changes have already been frequency analytically parameterized with posturography, sufficient data regarding the visual system are still missing. The aim of this study was to evaluate the influence of pathologic and simulated visual dysfunctions on the postural system by calculating the frequency analytic representation of the visual system throughout the frequency range F1 (0.03-0.1 Hz) of Fourier analysis. The study was divided into two parts. In the first part, visually handicapped subjects and subjects with normal vision were investigated with posturography regarding postural stability (stability effect, Fourier spectrum of postural sway, etc.) with open and closed eyes. The visually impaired and the normal group differed significantly in the frequency range F1 (p = 0.002). Significant differences of the postural stability between both groups were found only in the test position with open eyes (NO). The healthy group showed a significant loss of stability, whereas the impaired group showed an increased stability due to sufficient somatosensoric processes. Visually handicapped persons can compensate the visual information deficit through improved peripheral-vestibular and somatosensoric perception and cerebellar processing. In the second part, subjects with normal vision were examined under simulated visual conditions, e.g., hyperopia (3.0 D), reduced visual acuity (VA = 20/200), yoke prisms (4 cm/m) and pursuits (pendulum). Changes in postural parameters due to simulations have been compared to a standard situation (open eyes [NO], fixation distance 3 m). Visual simulations showed influence on frequency range F1. Compared to the standard situation, significant differences have been found in reduced visual acuity, pursuits and yoke prisms. A loss of stability was measured for simulated hyperopia, pendulum and yoke prisms base down. Stability regulation can be understood as a multi-sensoric process by the visual, vestibular, somatosensoric and cerebellar system. Reduced influence of a single subsystem is compensated by the other subsystems. Obviously the main part of reduced visual input is compensated by the vestibular system. Moreover, the body sway, represented by the stability indicator, increased in this situation.