Accurate two-dimensional eye tracker using first and fourth Purkinje images

Although a number of devices are currently in use for monitoring eye position, none is both accurate and convenient to use. Methods based on the use of contact lenses can provide high accuracy but have obvious inconveniences. Other techniques—e.g., skin-mounted electrodes, or eyeglass-mounted photoelectric pickups—are relatively convenient, but eye position can be measured to an accuracy of no better than about 0.5° to 1°. A novel eye-tracking instrument has been developed that makes use of two Purkinje images. The instrument operates in the infrared, so that it does not interfere with normal vision; it requires no attachments to the eye; it has a sensitivity and accuracy of about 1 min of arc, and operates over a two-dimensional visual field of 10° to 20° in diameter. The basic principle of the instrument is described, and operating records are shown.