Abstract
The detection of eye torsion is an important element for diagnosis of balance disorders, although it is rarely available in existing eye tracking systems. A novel method is proposed in this paper to provide robust measurement of torsional eye movements. A numerical approach is presented to estimate the iris boundary only according to the gaze direction, so the segmentation of the iris is more robust against occlusions and ambiguities. The perspective distortion of the iris pattern at eccentric eye positions is also corrected, benefiting from the transformation relation that is established for the iris estimation. The angle of the eye torsion is next measured on the unrolled iris patterns via a TM (Template Matching) technique. The principle of the proposed method is validated and its robustness in practice is assessed. A very low mean FPR (False Positive Rate) is reported (i.e., 3.3%) in a gaze test when testing on five participants with very different eye morphologies. The present method always gave correct measurement on the iris patterns with simulated eye torsions and rarely provided mistaken detections in the absence of eye torsion in practical conditions. Therefore, it shows a good potential to be further applied in medical applications.
Highlights
The image acquisition is set to 30 FPS in the current system, i.e., the interval time between two consecutive frames is about 33 ms. This frame rate was chosen because it is sufficient for most clinical tests that may require 3D eye movement tracking and it is commonly adopted by eye tracking systems that are available on the market for medical applications
The proposed iris segmentation method is more robust against occlusion and ambiguity than image-based approaches, because the iris boundary is computed according to the gaze direction, and the latter is estimated using the result of pupil segmentation, which is less sensitive to noises due to the smaller pupil size than the iris
The robustness of eye torsion measurement is often challenging in practice, so it is rarely proposed in current eye tracking systems that are available on the market
Summary
Eye torsion is an involuntary eye movement that aims to stabilize the vision during a head movement (i.e., head tilt). It is defined as a rotation of the eye around the LoS (Light of Sight). The LoS is the line that connects the point of regard and the center of the entrance pupil and it is used to indicate the gaze direction [1]. Torsional eye movement is an important element for diagnosis of balance disorders. It aims to provoke a compensatory torsional eye movement in the inverse direction of the head motion to keep a more stable image on the retina
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