Repeated visually-guided saccades improves postural control in patients with vestibular disorders

One of the most recent and promising theoreticalhypotheses for compensation of persistent asymmetry ofdynamic vestibulo-ocular gain is sensory substitution. Asa switch between oculomotor and vestibulo-ocular systems,saccadic eye movements are engaged in humans to compensatethe angular displacement of the head towards thelabyrinthine defective side thus preserving the foveal fixationof the target. This study focused on the possibility thatsaccadic eye movements might also compensate for theimpaired vestibulo-spinal reflexes and force the posturalsystem to a more effective control on upright stance andverified whether this sway-stabilizing effect could beapplied to patients with vestibular disorders and balancedysfunction. In the first experiment, 27 patients with unilaterallabyrinthine hypofunction, 24 patients with centralvestibular disorders and 24 healthy volunteers were evaluatedby static posturography in 3 different visual conditions:a) eye open with fixation of a steady target, b) eyeclosed, and c) while performing horizontal visually-guidedsaccades. The percentage of individuals with a decreasedbody sway area during the oculomotor task was found tobe higher in labyrinthine-defective patients as compared tothose with central vestibular disorders and controls. In thesecond experiment, 46 patients with vestibular disordersboth of central and peripheral origin, whose postural controlimproved by eye-tracking, as assessed by posturography,were later submitted to 12 consecutive training sessionsbased on repeated visually-guided saccades. Both thesaccadic performances and postural control improved in allpatients but a more pronounced effect was observed in thosewith peripheral vestibular disorders. Outcome of this rehabilitationtechnique was also corroborated by a generalreduction of the perceived overall impairment from balancedisorders as tested by a specific questionnaire.