Abstract
Purpose :
Previous studies noted that, paradoxically, defocus in one eye disrupts stereopsis and vergence responses more than defocus in both eyes. The goal of this study was to extend this work into larger naturalistic stimuli to determine the amount of anisometropia that is likely to disrupt oculomotor performance in a natural setting.
Methods :
Dichoptic grayscale natural images (SYNS database) of radii 1,2,4 or 8deg with a mean luminance surround were presented using a ProPixx projector, active circular polarizer, and rear-projection screen (67deg x 41deg). Participants viewed them through polarizer glasses from a distance of 70cm. The stimuli within each aperture radius underwent either a step change in disparity presented for 1.5s or a random walk in disparity velocity, while eye position was recorded with an Eyelink 1000. Defocus of 1,2,3 or 4D was simulated monocularly or binocularly for each participant’s current pupil size using convolution of the images with the appropriate PSF.
Results :
9 participants (19-54 years) provided complete datasets. Focused images of 8deg radius presented to both eyes resulted in typical reflex vergence disparity tuning functions (Busettini et al, 2001) peaking at 1deg disparity steps with mean±SD response amplitudes (last 0.25s) of 0.96±0.31deg. Bilateral defocus resulted in a reduction in these responses (0.59±0.33deg at 4D), while anisometropic defocus resulted in a greater reduction (0.39±0.51deg at 4D). Responses to crossed and uncrossed disparities were qualitatively similar. Smaller stimulus radii led to smaller amplitudes regardless of defocus. In the vergence tracking task the vergence peak correlation of 0.65 ± 0.11 at 8deg radius with focused stimuli was not significantly different from that for 4 and 2deg radii, whereas tracking performance was significantly poorer at 1deg stimulus radius (peak correlation of 0.54±0.12, p<0.001). Vergence peak correlation decreased with defocus at all stimulus radii, especially when presented monocularly (0.33±0.21 at 4D unilateral defocus and 8deg radius vs. 0.51±0.14 at 4D bilateral defocus).
Conclusions :
When managing patients at risk for anisometropic amblyopia or strabismus, or when prescribing monovision for adults, the evidence here suggests that a difference in defocus between the eyes of 2D or greater puts the patients at risk for unstable vergence performance.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.