Dynamic Control of Primary Eye Position as a Function of Head Orientation Relative to Gravity

The particular orientation of Listing’s plane in the head depends on head posture relative to gravity. The spatial orientation of slow phase rotation axes changes smoothly as a function of head orientation. This becomes obvious when plotting torsional versus vertical slow phases of nystagmus at different head orientations. The instantaneous head orientation relative to gravity determined the torsional stance of the eye at any instant of time as a function of momentary gaze direction. The spatial orientation of fast phase rotation axes as a function of horizontal and vertical gaze depended on instantaneous head orientation relative to gravity in a similar way as that of slow phases. The important point here is that, similarly as in the static situation, there is a direction of minimal torsion which changes dynamically its orientation in space as a function of head orientation relative to gravity.