Vertical and horizontal eye displacement during static pitch and roll postures.

The positions of both eyes were measured objectively in the dark following "look straight ahead" instructions for 16 subjects at 27 combinations of static pitch and roll postures over 360 degrees of space, using an infrared video technique. Shifts in vertical version, or the doll reflex, varied sinusoidally with pitch and roll angle. At 0 degree roll, the average response has a peak-to-trough amplitude of 9.28 degrees and is symmetric about a downward eye position of 4.63 degrees. The proposed Dual Otolith Model (DOM), based on a combination of utricular and saccular inputs, provided excellent fits to the present data (R2 = 0.876) and to the data of previous studies (R2 = 0.916 to 0.994). Deviations in horizontal version varied sinusoidally with roll angle, with no significant effect of pitch angle. In general, clockwise (right-ear-down) rolls produced rightward eye movements, and counterclockwise (left-ear-down) rolls produced leftward eye movements. The average versions were symmetric about a leftward eye position of 1.14 degrees, with a peak-to-trough amplitude of 3.76 degrees. The data were well represented by the proposed Horizontal Version Model (HVM; R2 = 0.796), which depended only on utricular input.