Upper eyelid movements measured with a search coil during blinks and vertical saccades

Upper eyelid movements were recorded in nine human subjects by mounting a miniature coil of wire directly on the eyelid and subjecting the search coil to a vertically directed alternating magnetic field. The metrics of blinks and lid movements accompanying saccades were described by "main sequence" relationships, linking maximum velocity to amplitude and duration to amplitude. In general, lid movements were faster than those reported previously in the literature, but there was considerable intersubject variability. On average, the main sequence relationships for blinks were independent of either starting lid position or whether the blinks were generated spontaneously, reflexively, or voluntarily. For the down phase of the average blink, both the maximum velocity and duration increased almost linearly with amplitude. The maximum velocity of the down phase was faster than that of the up phase. For lid movements accompanying vertical saccades, the maximum velocities in the up and down directions were similar and increased nonlinearly with amplitude, saturating at about 120 mm/sec (approximately 450 degrees/sec). Duration increased approximately linearly with amplitude. The down phases of blinks were much faster than those of saccade-related lid movements. By comparison, the maximum velocities of the up phase of blinks and of saccade-related lid movements were almost equal. The large intersubject variability suggests caution when using normative data to interpret abnormal lid motion for clinical purposes.