Applying double magnetic induction to measure two-dimensional head-unrestrained gaze shifts in human subjects.

This study compares the performance of a newly developed gaze (eye-in-space) measurement technique based on double magnetic induction (DMI) by a custom-made gold-plated copper ring on the eye with the classical scleral search coil (SSC) technique to record two-dimensional (2D) head-unrestrained gaze shifts. We tested both systems simultaneously during head-free saccades toward light-emitting diodes (LEDs) within the entire oculomotor range (+/-35 deg). The absence of irritating lead wires in the case of the DMI method leads to a higher guarantee of success (no coil breakage) and to less irritation on the subject's eye, which results in a longer and more comfortable measurement time. Correlations between DMI and SSC signals for horizontal and vertical eye position, velocity, and acceleration were close to 1.0. The difference between the SSC signal and the DMI signal remains within a few degrees. In our current setup the resolution was about 0.3 deg for the DMI method versus 0.2 deg for the SSC technique. The DMI method is an especially good alternative in the case of patient and laboratory animal gaze control studies where breakage of the SSC lead wires is particularly cumbersome.