Abstrakt
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 signifcant diference 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 signifcant change in VA in emmetropic subjects.