In a low-cost laboratory setup, we compared visual acuity (VA) for stimuli rendered with Zernike aberrations to an equivalent optical dioptric defocus in emmetropic individuals using a relatively short observing distance of 60 cm. The equivalent spherical refractive error of + 1, + 2 or + 4 D, was applied in the rendering of Landolt Rings. Separately, the refractive error was introduced dioptrically in: (1) unchanged Landolt Rings with an added external lens (+ 1, + 2 or + 4 D) at the subject's eye; (2) same as (1) but with an added accommodation and a vertex distance adjustment. To compare all three approaches, we examined VA in 10 healthy men. Stimuli were observed on a PC CRT screen. For all three levels of refractive error, the pairwise comparison did not show a statistically significant difference between digital blur and accommodation-plus-vertex-distance-adjusted dioptric blur (p < 0.204). The best agreement, determined by Bland-Altman analysis, was measured for + 4 D and was in line with test-retest limits for examination in the clinical population. Our results show that even for a near observing distance, it is possible to use digitally rendered defocus to replicate dioptric blur without a significant change in VA in emmetropic subjects.

Biosciences Institute Faculty of Medical Sciences Newcastle University Newcastle UK

Department of Experimental Psychology University of Oxford Oxford UK

Department of Medical Biophysics Faculty of Medicine in Hradec Kralove Charles University Hradec Kralove Czech Republic

Department of Pathological Physiology Faculty of Medicine in Hradec Kralove Charles University Hradec Kralove Czech Republic

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