Torsional component of microsaccades during fixation and quick phases during optokinetic stimulation.

While many studies have characterized the eye movements during visual fixation, includ-ing microsaccades, in most cases only horizontal and vertical components have been rec-orded and analyzed. Thus, little is known about the torsional component of microsaccades. We took advantage of a newly developed software and hardware to record eye movements around the three axes of rotation during fixation and torsional optokinetic stimulus. We found that the average amplitude of the torsional component of microsaccades during fixation was 0.34 ± 0.07 degrees with velocities following a main sequence with a slope comparable to the horizontal and vertical components. We also found the size of the tor-sional displacement during microsaccades was correlated with the horizontal but not the vertical component. In the presence of an optokinetic stimulus a nystagmus was induced producing a more frequent and larger torsional quick phases compared to microsaccades produced during fixation with a stationary stimulus. The torsional component and the vertical vergence component of quick phases grew larger with higher velocities. Addition-ally, our results validate and show the feasibility of recording torsional eye movements using video eye tracking in a desktop mounted setup.