Abstract
Purpose :
Most clinical and research grade ophthalmoscopes rely on the subject’s ability to fixate on a target to minimize eye movements during data capture. Due to the small size of the beam at the ocular pupil in most conventional ophthalmoscopes, the retina cannot be imaged during large eye movements. Our goal is to develop an instrument capable of tracking the eye using retinal imaging even during large saccades.
Methods :
A monocular ophthalmoscope was custom-designed and assembled, comprising of (1) a sub-system for illuminating the eye with 850 nm light wherein the beam size at the pupil of the eye can be up to 15 mm in diameter, (2) a back-illuminated stimulus target at 635 nm, (3) an adjustable aperture (2 to 6 mm in diameter) mounted on a 2-axis stage, located at a plane conjugate to the pupil of the eye, (4) an imaging channel with a CMOS camera for imaging the retina over a 45 deg field of view, and (5) a pupil-tracking camera at 940 nm. Two near-emmetropic subjects participated in this study. Their eyes were positioned at the exit pupil of the ophthalmoscope. Videos of the anterior and posterior segments of the eye were captured simultaneously while the subjects made saccades of varying amplitudes. Images from the pupil camera were used to determine the pupil position and the aperture was dynamically steered to maximize light entering the eye.
Results :
The steered aperture minimized backscatter from the iris, sclera, and skin and improved contrast of the retinal images. Shadows cast by the stimulus target were visible in the retinal images, providing estimates of where the subjects were gazing. Retinal structures such as the optic disk and vasculature were visible during saccades up to 20 degrees in amplitude.
Conclusions :
To our knowledge, this is the first demonstration of continuous retinal imaging during large amplitude saccades. This is a step towards ground-truth gaze-tracking in a freely gazing eye.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.