EVALUATION OF A VIDEO TRACKING DEVICE FOR MEASUREMENT OF HORIZONTAL AND VERTICAL EYE ROTATIONS DURING LOCOMOTION

We have evaluated a video-based method for measuring binocular horizon tal and vertical eye movements of human subjects by comparing it with the magnetic search coil technique. This video tracking system (VTS) u ses multiple infrared light sources and small video cameras to simulta neously measure the positions of reflected corneal images and the cent er of the pupil. The system has a linear range of approximately +/-40 degrees horizontally and +/-30 degrees vertically, a sampling rate of 120 Hz (180 Hz with the head fixed), and system noise with standard de viation of < 0.04 degrees. The binocular eye-tracking system is light- weight (190 g), being mounted on goggles that, with the eyes in primar y position, permit a field of view of 60 degrees horizontally and vert ically. The VTS is insensitive to translations of the tracker relative to the eyes. By placing the video preprocessing unit on a cart, eye m ovements may be recorded while subjects walk through distances up to 1 00 feet. In comparison with the magnetic search coil technique, the VT S generally provides reliable measurements of horizontal and vertical eye position; eye velocity is noisier than corresponding coil signals, but superior to electro-oculography.