Fuseina Safianu¹, Eswar Kurni¹, Bhagya L Marella¹, T Rowan Candy¹; ¹School of Optometry, Indiana University, Bloomington, IN,USA

Objective: Eye alignment is driven by the distribution of retinal disparities across scenes. The ability to maintain alignment depends on scene structure and the observer’s ability to encode disparity. This study asked how defocus and peripheral sensitivity combine across the visual field in limiting maintenance of eye alignment. Method: Dichoptic grayscale natural images (76x42deg SYNS database) were presented at a 70cm viewing distance using a PROPixx projector (RB3D mode, VPixx) and computationally-simulated bilateral or unilateral defocus (IRIS software, for participants’ pupil size and 0, 1, 2, and 4D). A circular textured disk of 1/f noise with varying radii (1, 2, 4, 8, 12, and 16deg) was presented in the center of the image. The disk followed a 30s random walk in velocity between disparities of ±4deg. Two continuous tracking vergence trials to the moving disk were recorded from 5 adult functionally emmetropic subjects (age: 28 to 56yrs) using an Eyelink-1000 (SR-Research). Results: Peak correlations were computed by cross-correlating velocities of the stimulus and responses. For bilateral defocus, vergence peak correlations increased with disk radius (p<0.001). For anisometropic defocus, vergence correlations increased with disk radius and decreased with defocus (p<0.001). To further understand the anisometropia, peak correlations were computed for the defocused and focused eye gaze responses separately. Both the focused and defocused eye peak correlations changed significantly with both radius and defocus (p<0.001), although with a bigger effect of defocus in the defocused eye. Restricting the defocus to the central disk only did not change the qualitative results. Conclusion: The largest reduction in vergence performance occurred with smaller disks and differences in defocus between the eyes. These conditions are of concern for anisometropic children and patients using monovision, whose defocused eye would have both limited sensory input and ocular motor performance.

Acknowledgements: NEI RO1 EY014460