eye tracking systems by Arrington Research, Inc.

Eye Tracking and Torsion
Free-Gaze Real-Time Ocular Torsion
Torsion is the rotation of the eye-ball about the line of sight, i.e. rotation about the z-axis. ViewPoint measures torsion in degrees of rotation and stores the values in the ASCII format data file. Data can also be accessed real-time from other applications. Real-time feed-back is displayed in the PenPlot window.
ocular torion measurement
Torsion from Head Roll Torsion from head roll
Torsion from Saccades Torsion from saccades

Torsion Measurement is available as an additional option. Item 0035 $1,998.