Episcleral surface tracking: challenges and possibilities for using mice sensors for wearable eye tracking

Video-based eye trackers (VETs) have become the dominant eye tracking technology due to its reasonable cost, accuracy, and easy of use. VETs require real-time image processing to detect and track eye features such as the center of the pupil and corneal reflection to estimate the point of regard. Despite the continuous evolution of cameras and computers that made head mounted eye trackers easier to use in natural activities, real-time processing of high resolution images in mobile devices remains a challenge. In this paper we investigate the feasibility of a novel eye-tracking technique intended for wearable applications that use mice chips as imaging sensors. Such devices are widely available at very low cost, and provide high speed and accurate 2D tracking data. Though mice chips have been used for many purposes other than a computer's pointing device, to our knowledge this is the first attempt to use it as an eye tracker. To validate the technique, we built an episcleral database with about 100 high resolution episcleral patches from 7 individuals. The episclera is the outer most layer of the sclera, which is the white part of the eye, and consists of dense vascular connective tissue. We have used the patches to determine if the episclera contains enough texture to be reliably tracked. We also present results from a prototype built using an off-the-shelf mouse sensor. Our results show that a mouse-based eye tracker has the potential to be very accurate, precise, and fast (measuring 2.1' of visual angle at 1 KHz speed), with little overhead for the wearable computer.