Suppression of the Vertical Vestibulo-ocular Reflex in Older Persons at Risk of Falling

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Abstract
A case-control design was used to assess eye-head-trunk coordination for community-dwelling elders performing a stand-walk task. Eighteen elders with a high risk of falling were matched to 18 subjects with low risk on the basis of age, living status (living alone or with someone) and category of residence (independent living or assisted living facility). Standard electro-oculography was used in conjunction with an electromagnetic tracking device to measure eye and head-trunk motion, respectively. For the low-risk group, the mean slope of gaze-head and gaze-trunk relationships was significantly greater than zero (0.91 and 0.64, respectively), whereas high-risk elders did not demonstrate slope magnitudes significantly different from zero (0.52 and 0.16, respectively) due to large inter-subject variations. While the majority of subjects showed some counter-rotation of the eyes with head pitch, a greater percentage of subjects in the high-risk group did not suppress this response and consequently gaze and gaze velocity overcompensated for head pitch. These findings suggest that the vertical vestibulo-ocular reflex is not adequately suppressed during the stand-walk task in elders who are at a high risk of falling. Possible mechanisms contributing to these findings are discussed.