Robust eye tracking based on multiple corneal reflections for clinical applications

A set of methods in terms of both image processing and gaze estimation for accurate eye tracking is proposed. The eye-tracker used in this study relies on the dark-pupil method with up to 12 corneal reflections and offers an unprecedented high resolution imaging of the pupil and the cornea. The potential benefits of a higher number of glints and their optimum arrangement are analyzed considering distinct light sources configurations with 12, 8, 6, 4, and 2 corneal reflections. Moreover, a normalization factor of the pupil-glint vector is proposed for each configuration. There is a tendency for increasing accuracy with the number of glints, especially vertically (0.47 deg for 12 glints configuration versus 0.65 deg for 2 glints configuration). Besides the number of corneal reflections, their arrangement seems to have a stronger effect. A configuration that minimizes the interference of the eyelids with the corneal reflections is desired. Finally, the normalization of the pupil-glint vectors improves the vertical eye tracking accuracy up to 43.2%. In addition, the normalization also limits the need for a higher number of light sources to achieve better spatial accuracy.