Static and dynamic properties of vergence-induced reduction of ocular counterroll 

MJ. Mandelli, H. Misslisch, B. Hess

Vestibulo-Oculomotor Laboratory, Department of Neurology, University Hospital Zurich, Switzerland

This study examined the static and dynamic properties of vergence-induced suppression of ocular counterroll in near vision. We found that binocular torsion was suppressed by about 70%, on average. Latency and duration of the change in torsional eye position depended–for each eye differently–on body roll and the direction of depth refixation. For instance, in left-ear down head orientations during far-to-near refixations, the latencies of the left eye were smaller and the durations were larger than those of the right eye. In other words, both eyes reached their positions required to fixate the target roughly at the same time. The former finding is in accordance with a previous study that used a global approach in quantifying binocular torsion in far and near viewing. The latter result can be explained by the fact that the eye position planes of each eye are rotated temporally when the eyes converge (binocular extension of L2). Coming from or aiming at a common torsional value (normal ocular counterroll) in far-to-near or near-to-far refixations, the size of the torsional eye movement differs in the two eyes. In coordinating the kinematics of the two eyes, the brain compensates for these differences by adjusting the dynamics of eye motion.

Ocular counterroll: When we turn our head or our body on one side, each eye rotates around a naso-occipital axe in the opposite direction of the head or body rotation.