Binocular eye tracking with the Tracking Scanning Laser Ophthalmoscope

•Modification of the tracking SLO allows simultaneous recording of both eyes.•Sensitivity of tracking was found to range between 0.2 and 0.6 arc min.•Vertical vergence had an SD of 1–2 arc min.

The development of high magnification retinal imaging has brought with it the ability to track eye motion with a precision of less than an arc minute. Previously these systems have provided only monocular records. Here we describe a modification to the Tracking Scanning Laser Ophthalmoscope (Sheehy et al., 2012) that splits the optical path in a way that slows the left and right retinas to be scanned almost simultaneously by a single system. A mirror placed at a retinal conjugate point redirects half of each horizontal scan line to the fellow eye. The collected video is a split image with left and right retinas appearing side by side in each frame. Analysis of the retinal motion in the recorded video provides an eye movement trace with very high temporal and spatial resolution.Results are presented from scans of subjects with normal ocular motility that fixated steadily on a green laser dot. The retinas were scanned at 4° eccentricity with a 2° 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 to range from 0.25 to 0.5 arc min SD for three subjects. In the binocular recordings, the left eye/right eye difference was 1–2 arc min SD for vertical motion and 10–15 arc min SD for horizontal motion, in agreement with published values from other tracking techniques.