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K. Irsch, H. S. Ying, A. Kurz, N. A. Ramey, R. S. Adyanthaya, D. L. Guyton; Head Movement Compensation for Novel Haploscopic Eye Tracking Apparatus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1803.
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To describe a video-based head tracking technique to compensate for in-plane head movements during iris-tracking video-oculography with a tilting haploscope.
Custom MATLAB software, interfacing with IRIS commercial eye tracking software (Chronos Vision; Berlin, Germany), was developed for image acquisition and offline analysis. Head movements were monitored by tracking black dots on the subject’s inner canthi, which remained fairly stationary during eye movements. Both dot and pupil positions were computed using feature detection based on the Hough Transform modified for ellipses. Ocular torsion was determined with IRIS’s polar correlation algorithm, utilizing natural iris landmarks. Using the inter-dot distance and the relative vertical shifts of the dots during head motion, each video frame was rotated, then conjugate dot translation was subtracted, and pupil tracking was performed to eliminate the effect of head movements from the eye movement data. This technique was verified using normal subjects who were asked purposely to move their heads, straining against the bite bar, while maintaining central fixation on the targets.
The representative figure demonstrates compensation for a normal subject recorded with head straight and on attempted right or left head tilt against the bite bar. Traces showed elimination of erroneous eye movements of up to 11º.
Tracking black dots placed on the inner canthi is an effective tool to compensate for horizontal, vertical, and torsional in-plane head movements during the iris-tracking method of video-oculography.
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