Visual postural performance after loss of somatosensory and vestibular function.

Visual stabilisation of body sway in a patient with severe deficits of the vestibular system (due to gentamicin treatment) and the somatosensory system (due to polyneuropathy) was studied. With eyes open the patient was able to stand and walk slowly. With eyes closed he lost balance within one second. In order to optimise visual stabilisation he intuitively searched for nearby visual targets. His postural sway was recorded using posturography. His balance performance deteriorated significantly beyond a distance of 1 m between the eyes and the surrounding objects and with visual acuity below 0.3 (experimentally achieved with semitransparent plastic foils). With flicker illumination of decreasing frequencies of the visual surround he needed at least a visual input rate of 17 Hz in order to maintain an upright body position. The data provide clinical evidence for rapid visuo-spinal control of posture.