Subjective vergence error at near during active head rotation.

There exists some controversy regarding the effects of active horizontal head rotation on vergence error. We used a conventional, Ogle-type, subjective fixation disparity apparatus to measure vergence error at near over a full range of horizontal head-rotation frequencies. Change in vergence error rarely exceeded 10 min arc. This finding demonstrates the adequacy of the vergence system to maintain relatively accurate bifixation at near and to allow for continuous maintenance of binocular sensory-motor integrative ability, even in the presence of system perturbations.