Abstract
Purpose :
Retinal videos recorded with Tracking Scanning Laser Ophthalmoscopy (TSLO) can be used to determine the direction of gaze with exceptional spatial and temporal precision. While previously used to determine characteristics of fixational eye movements, here we evaluated the feasibility of tracking larger horizontal saccades, while simultaneously tracking the pupil using a conventional video-based eye tracker.
Methods :
A TSLO (C. Light Tech.) with a 7° raster and 840 nm imaging beam was used to image the right eye of each observer (2 males and 1 female, normal ocular health). Stimuli were presented on a 5in OLED monitor positioned above the observer, optically overlaid with the imaging raster using a cold mirror and a plus lens to relax accommodation. An Eyelink 1000+ viewed a reflected image of the left eye, which was passive. A small annular target (outer ring: 15’ diameter, inner ring: 6’ diameter) moved from left to right in four steps of ⅓°, with a duration of 500ms at each position. This sequence was repeated 6 times to yield ~30s eye traces containing horizontal reading-like eye movements.
Results :
We analyzed 3-6 eyetrace records for each subject. First, the raw eye positions from each system were resampled to a common sampling rate of 1kHz, then cross-correlated between systems to determine optimal temporal alignment. After alignment, correlations between the X positions were high (0.66 +/- 0.13, across subjects), as the task-related horizontal motion was captured well by both systems. Correlations between the Y positions were smaller (0.15 +/- 0.13) but still resulted in a unique cross-correlation peak in good agreement with the horizontal peak. The mean difference in X positions and Y positions were 0.502’ (SD=23.21’) and 0.05’ (SD=7.22’), respectively. Traces from both devices had similar power spectral densities with 1/f frequency content, although the Eyelink had larger overall magnitude.
Conclusions :
Eye traces were reliably obtained from the TSLO in the presence of horizontal saccades, indicating its potential utility in studying reading eye movements. Separating the imaging and stimulus channel using an external display allows presentation of stimuli across a larger spatial region, not limited by the size of the raster. Simultaneous video-based eye tracking permits the observation of coordinated motion in the anterior and posterior segments of the eye.
This is a 2020 ARVO Annual Meeting abstract.