Eye-head coordination during lateral gaze in normal subjects.

To elucidate the characteristics of eye-head coordination during lateral gaze, eye, head and gaze displacements to 10 degrees, 20 degrees, 30 degrees, 40 degrees, and 50 degrees target presentations were analysed quantitatively in 10 normal subjects. Head displacement was recorded without mechanical restraint by a newly devised apparatus containing two terrestrial magnetic sensors. Eye movements were recorded using d.c. electro-oculography through bitemproal leads. (1) As the target angle increased, the latency of eye movement increased while that of head movements decreased. (2) The rise times of eye and head movements increased almost linearly with the target angle. (3) The maximum velocity of eye movement averaged 292 degrees/sec at 10 degrees, increased to 398 degrees/sec at 20 degrees, and remained unchanged thereafter. The maximum velocity of head movement increased linearly with the target angle. (4) The head displacement at the end of eye saccade became relatively larger as the target angle increased, though the sum of eye and head displacements, i.e. gaze, agreed with the target angle. (5) At the final resting position, the percentage of target angle attained by head displacement decreased from 93% to 10 degrees to 62% at 50 degrees. However, gaze displacement was exactly the same as the target angle, with little dispersion for each angle of gaze shift, indicating that the head rotation detector is an accurate device for recording horizontal head movement under natural conditions.