Field-wide Quantification of Aniseikonia Using Dichoptic Localization

SIGNIFICANCE: We validated a novel paradigm to measure aniseikonia across the visual field and used a mathematical approach that is able to describe the magnitude and shape of aniseikonia in a concise, clinically meaningful fashion. PURPOSE: The measurement of aniseikonia has been performed clinically for more than half a century; however, amalgamation of field-wide local variations in binocular spatial localization into clinically applicable global metrics has yet to be attempted. Thus, the goal of the current study was twofold: first, to measure field-wide aniseikonia and second, to compare how local and global metrics each capture optically induced aniseikonia. METHODS: Twelve visually normal observers performed a dichoptic localization task at 24 locations in the visual field. This was done in four conditions: (A) while wearing red-green filters, (B) while wearing green-red filters, (C) while wearing a monocular 5% overall size lens, and (D) while wearing a monocular 6% meridional size lens. The physical settings at perceptual equality were then used to compute both local (relative magnification) and global (coefficients for Zernike terms) descriptors of aniseikonia. RESULTS: The comparison of each lens condition to the baseline condition confirmed predicted shifts in both the sign and magnitude of aniseikonia at both the local and global levels; however, the intraobserver levels of precision were moderate, and systematic underestimations were present across all locations in conditions C and D. CONCLUSIONS: Local and global analyses derived from dichoptic localization data were both able to capture optically induced changes in binocular spatial perception; however, solutions that address the diagnostic and therapeutic challenges associated with this paradigm are needed before clinical implementation can proceed.