Ultrafast retinal tracker for quantification of fixational and saccadic motion of the human eye

Abstract

Purpose : To demonstrate that a retinal eye-tracking system based on scanning laser ophthalmoscopy principle that acquires 1240 frames per second is able to quantify fixational eye movements and saccades exceeding the frame size in both horizontal and vertical directions with an angular resolution of up to 0.05 arcmin RMSE.

Methods : : A scanning laser ophthalmoscopy setup with resonant 2D MEMS scanning mirror operating at 20kHz in fast axis and 640 Hz slow axis was designed and assembled. It allows for the acquisition of 1240 images of the retina per second with approx. 4430 pixels each from of 3°x3° field of view. The data points acquired along the resulting scanning pattern are resampled to uniformly sampled frame and affine transform between consecutive frames is calculated to find the displacement between the two frames. Additional wide-field SLO device operates at 20 frames to provide images (800x600 pixel each) of ~24°x15° region of the retina that is used to allow for finding retinal features facilitating precise retinal tracking. The images from both devices are captured by a custom-built electronics and transferred to synchronizing computer. Automated data processing allows for the reconstruction of the retinal trajectory followed by saccade detection and quantification (amplitude, velocity, and acceleration of saccades). To control the gaze of the subjects during experiments, the system was equipped with a dynamic fixation target presentation screen.

Results : The ability of the retinal eye tracker to provide high-resolution retinal trajectories and to quantify the retinal motion was proven on 30 eyes of 20 healthy volunteers aged between 25 and 70 y.o. The patients performed visual tasks comprising fixation and forced saccades of magnitudes between 1 deg and 8 deg. Achieved accuracy in retinal trajectory estimation was measured to be less than 0.05 arcmin in fixation experiments. Over 40 thousand saccades were observed with the smallest saccade of ~1.7arcmin.

Conclusions : The results show that an ultrafast retinal tracker can be used for providing information on retinal trajectories with high angular (<0.05arcmin) and temporal resolution (<800µs) as well as with high amplitude motion exceeding the size of tracker frame.

This is a 2020 ARVO Annual Meeting abstract.