Aging does not affect the accuracy of vertical saccades nor the quality of their binocular coordination: a study of a special elderly group
(Le vieilissement n'affecte pas la précision des saccades verticales ni la qualité de la coordination binoculaire)

Yang Q, Kapoula Z.
IRIS Group, Laboratoire de Physiologie de la Perception et de l'Action, UMR 7152, CNRS-Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France. qing.yang@college-de-france.fr

SUMMARY : Fine binocular coordination of vertical saccades is a complex process requiring appropriate distribution of innervations to all six extraocular muscles. Loss of such coordination causes vertical binocular disparities that are particularly bothersome. We studied the quality of binocular control of vertical saccades in healthy subjects, 11 young adults (20-28 years) and 11 elderly adults (63-75 years). We used LED targets at 7.5 degrees or 15 degrees from the center (fixation), up or down in four conditions: gap and overlap tasks, each done at two distances--near (40 cm) and far (150 cm). Vertical eye movements were recorded with video-oculography (CHRONOS). The results showed: aged subjects performed vertical saccades as accurately as young subjects. Importantly, the binocular coordination of vertical saccades was well preserved in the elderly; the mean difference of vertical saccades between the two eyes was 0.10 degrees and 0.09 degrees in young and elderly subjects, respectively. Upward saccades were associated with divergence, downward ones with convergence. This secondary phenomenon was also the same and of the similar amplitude for young (1.30 degrees ) and elderly (1.25 degrees) subjects. Thus, despite its complexity, the quality of binocular coordination of vertical saccades remains intact with age. The other observations are mostly dependent of several aspects on the direction (up/down), viewing distances and eccentricities; the horizontal vergence during or after vertical saccades was found to be larger for downward saccades than for upward saccades, for saccades at far distance than at close, and for the more eccentric targets (15 degrees versus 7.5 degrees). All these phenomena are the same for both young and elderly subjects. We conclude that the accuracy and the binocular coordination of vertical saccades, at least for target steps less than 15 degrees , are preserved in elderly subjects <75 years who maintain good physical and intellectual form. The data are consistent with the idea of the existence of non-aging system function in the human CNS.

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