The Limitations on Vergence Responses to Naturalistic Images Resulting From Simulated Central Scotomas and Defocused Peripheral Retina.

PURPOSE: Clinical visual disorders are associated with interocular suppression and scotomas of the central visual field. The goal of this study was to understand the ability of the peripheral retina to drive reflex vergence responses in the presence of refractive defocus.

METHODS

Vergence responses to steps in horizontal disparity were recorded from functionally emmetropic adults (15-51 years of age) viewing grayscale outdoor natural images. Mean luminance central scotomas of 0°-25° radius in 5° steps were simulated in Experiment 1. In a second experiment, bilateral (1.50 D and 3.00 D) or unilateral (0, 0.75 D, 1.50 D, 2.25 D and 3.00 D) defocus, computed for each participant's pupil size, was simulated with scotoma radii of 0°, 5°, 8° and 10°.

RESULTS

Vergence responses to these disparity steps demonstrated a stereotypical tuning function in the absence of scotomas or defocus. In Experiment 1, bilateral scotoma radii of 10° or more led to significant decreases in open-loop vergence response amplitude (p < 0.001 for all). In Experiment 2, there were significant reductions in open-loop vergence responses resulting from unilateral (p < 0.001) but not bilateral defocus (p = 0.93). The effect of radius was significant, with no effect of bilateral versus unilateral scotoma format.

CONCLUSION

These data characterise the ability of the peripheral retina to maintain eye alignment for naturalistic images in the presence of central scotomas or suppression, and defocus. They suggest that vergence performance is reduced for natural images with bilateral and unilateral central scotomas, and indicate a need for refractive correction of anisometropia >1.50 D in order for the peripheral retina to support vergence function fully.