Ethan Pirso¹ (), Jude Mitchell², Curtis Baker¹; ¹McGill University, ²University of Rochester

For animal subjects, or human patients who have difficulty with conventional measurement methods, finding the best optical correction for refractive errors can be challenging. Refractive corrections are of growing concern in vision research due to the high prevalence of myopia in humans, but also with some colony-reared animals used in research. Traditional methods like psychophysical paradigms require extensive training or retinoscopy, which in animals requires anesthesia. However, tracking a moving target on a blank background is a natural task that is relatively easy for subjects to learn and execute. Here we used continuous psychophysics and eye tracking to measure contrast thresholds and assess refractive errors. Using custom MATLAB software with PsychToolbox-3 and an EyeLink 1000 eye tracker, we evaluated refractive errors by monitoring contrast sensitivity during dynamic visual stimulus tracking with gradually decreasing contrast. Applying this approach to the task of tracking a Gabor stimulus, we evaluated seven spherical lens powers, from -3 to +3 diopters, in successive runs on two human subjects . Each contrast sensitivity measurement necessitated less than a minute of eye tracking data. Contrast thresholds were derived from the positional errors between the target stimulus and the subjects' gaze positions. A plot of contrast threshold vs. lens power showed a clear dependence on positive diopter values and shallow dependence on negative ones, likely due to partial compensation from accommodation. We found that each subject’s optimal lens power coincided with their previously measured corrected-to-normal vision. Our findings demonstrate the utility of continuous psychophysics integrated with eye tracking for more ecologically valid measurements of contrast sensitivity and refractive errors. This method could be used for clinically challenging human populations, and might be adapted for non-human primates such as marmosets or macaques, extensively used in vision research, thereby eliminating the need for anesthesia in retinoscopy or prolonged behavioral training.

Acknowledgements: Funded by Canadian NSERC (RGPIN-2023-03559) and CIHR (MOP-119498) grants to CB.