The Coordination Between the Lid and Eye During Vertical Saccades
A close coordination between vertical eye and lid movements is required to allow the lid to afford the eye maximal protection without obscuring vision. A casual observation of the vertical tracking movements of human subjects reveals a tight coupling indeed between lid and eye during slow vertical gaze changes. It is not known, however, whether this tight coupling also occurs during vertical saccades. Conceivably, a tight coupling is not required since saccadic eye movements per se already are accompanied by transient impairments of vision (Brooks and Fuchs 1975). Furthermore, the coupling for upward and downward saccades may be quite different since the levator palpebrae muscle reportedly raises the eyelid for all upward movements, but no muscle participates actively in lowering the lid during downward eye movements (Evinger et al. 1984; downward lid movements during blinks, however, are accomplished by the orbicularis oculi muscles).
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