We developed a new binocular eye tracking system by adopting a USB-3.0 digital camera that provides high sensitivity, resolution and frame rate. The system is non-invasive and inexpensive and can be used for monkeys and humans. Infrared light illuminates two eyes and the reflected image of the iris and the black image of the pupil of each eye are captured by the camera. The center of the pupil is calculated and tracked over time. The system was originally developed to measure movements of one eye. In the present study, we have improved it for binocular eye movements by adopting a new wide-field, hi-resolution, and hi-frame-rate camera. Since the camera has a 2048x2048 pixels resolution, we can capture the images of both eyes simultaneously and calculate positions of the two eyes at each frame. The eye position data can be read out on line via computer network.
The adoption of the WINDOWS 7/8/8.1 x 64 as the operation system makes this binocular eye tracking system user-friendly. Because of the high frame rate of the digital camera, the sampling rate of the system can be as high as 700Hz. By using this system, we succeeded in characterizing vergence eye movements of humans when ocular fixation shifts between two targets placed at different distances in the 3-D space.