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Scott Stevenson, Christy Sheehy, Austin Roorda; Binocular Scanning Laser Ophthalmoscope design for eye tracking. Journal of Vision 2013;13(15):P29. doi: 10.1167/13.15.64.
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We describe a modification to the Tracking Scanning Laser Ophthalmoscope (Sheehy et al. 2012) that adds a second eye channel so that left and right retinas are scanned simultaneously by a single system. A mirror placed at a retinal conjugate point redirects half of each horizontal scan line to the fellow eye, so that left and right eye position samples are collected alternately at the 15.4 kHz line scan rate. The resulting video is a split image with left and right retinas appearing side by side in each frame.
We present results from scans of subjects with normal ocular motility who fixated steadily on a green laser dot. The retinas were scanned at 4 degrees eccentricity with a 2 degree square field. Eye position was extracted offline from recorded videos with an FFT based image analysis program written in Matlab. The noise level of the tracking was estimated by splitting a monocular scan into left and right halves and extracting eye motion independently for each half. The difference was 0.25 to 0.5 arc minutes SD for three subjects. In the binocular recordings, the left eye / right eye difference was typically around 2 arc minutes for vertical motion and 10 to 15 arc minutes for horizontal motion, in agreement with published values from other tracking techniques.
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