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Marianna Butera, Alina Sample, Jeffrey LeBlanc, Kevin Willeford; Precision and Repeatability of a Dichoptic Localization Paradigm Designed to Measure Aniseikonia. Journal of Vision 2020;20(11):408. doi: https://doi.org/10.1167/jov.20.11.408.
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© ARVO (1962-2015); The Authors (2016-present)
Asthenopia is common in patients with aniseikonia, a clinical condition in which the spatial localization of objects differs between each eye. There is intra-observer variability and questionable repeatability in tests which are currently utilized; furthermore, these tests can only quantify spherical or meridional aniseikonia at limited locations in the visual field. The goal of our experiment was two-fold: first, to quantify the magnitude of aniseikonia at multiple locations and second, to assess the precision and repeatability of these measurements.
We used a dichoptic localization task in which 23 observers performed radial alignments at 24 locations in the visual field on two separate occasions. Observers compared the perceived eccentricity of a reference stimulus (left eye) to that of a test stimulus (right eye) while centrally fixating. The relative eccentricity between the test and reference stimuli at perceptual alignment was used to compute the degree of aniseikonia at each location. We then used Zernike polynomials as basis functions to describe the global pattern of aniseikonia. Location-specific confidence intervals and Bland-Altman analyses were used to quantify precision and inter-session repeatability, respectively.
The group mean precision was 1.18° and was dependent on visual field location. The smallest detectable change for each of the coefficients ranged from 9% (Z3) to 25% (Z2) aniseikonia. The inter-session change in CI width was related to the inter-session change in Z1, suggesting that an observer’s precision and accuracy changed in tandem.
We developed a novel paradigm to address several shortcomings of tests which are currently utilized. We believe the large intra-observer and inter-session variability may be explainable by continuous fluctuations and undercorrection of fixation disparity, which, if addressed with a gaze-contingent display, may render this paradigm highly repeatable and useful for clinical implementation.
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