Postural adjustments produced by moving visual (horizontal optokinetic) patterns.

The effects of horizontal optokinetic stimulation (HOKS) on postural sway were examined in 30 normal subjects aged 20 to 75 years. Fixed-platform posturography was evaluated with the eyes open and closed and during HOKS (20-100 degrees/sec) in the rightward and leftward directions. Forward-backward sway was greater in amplitude than lateral sway under all viewing conditions. Sway amplitude was greater with eyes closed than with eyes open. HOKS significantly enhanced sway amplitude in both directions; however, significant differences occurred only between velocity extremes. Compared to younger subjects, older subjects showed greater forward-backward sway with eyes closed and greater lateral sway during HOKS. HOKS produces a visual cue that conflicts with the other two sensory signals regulating posture (vestibular and proprioceptive systems). Such conflicting visual cues may contribute to serious postural instability and falls in the elderly. The addition of optokinetic stimuli to fixed-platform posturography may enhance its diagnostic value.