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Susana Marcos, Clara Benedi, Maria Vinas, Carlos Dorronsoro, Stephen A Burns, Eli Peli; Visual benefit of correcting High Order Aberrations in blue or green light: an optical effect?. Invest. Ophthalmol. Vis. Sci. 2018;59(9):654. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previous literature (Mclellan et al, Nature 2002) showed computationally that the presence of high order aberrations protects the eye from the degrading effect of chromatic blur. The current study evaluates the psychophysical impact of chromatic blur and equivalent defocus in subjects under natural (Nat) and Adaptive-Optics (AO) corrected aberrations.
A custom-developed AO system provided with a deformable mirror, Hartmann-Shack wavefront sensor, Badal optometer and a psychophysical channel was used to measure the subject’s aberrations and to evaluate the perceptual judgement of nearly monochromatic images in 10 subjects (ages:30±7; refractive error:-1.3±1.1 D). Prior to the experiment, wave aberrations were measured (827 nm) and the aberration correcting mirror state was searched. Subjects searched their subjective best focus in green (G). In Exp 1, subjects estimated (1-5) the quality of G images both at best focus and shifted by chromatic defocus (-0.87 D). In Exp 2, subjects estimated quality of G & blue (B) images, at best focus for G. Tests were done for AO & No-AO. The sum of individual scores of 108 images was used as an estimate of image quality. Modulation Transfer Functions (MTFs) for G (in-/out-of-focus) & B (at G best focus) were computed for all conditions and Strehl ratios (SR, up to 40 cpd) taken as optical metric. The benefit of AO-correction was evaluated in terms of score ratios (psychophysical, PSY) & SR ratios (optical, OPT).
AO shifted best focus by 0.34±0.96 D (experimental) & 0.24±0.07 D (SR-based prediction). AO-correction improved best-focused score ratio (AO/noAO, G) on average by 1.17±0.27/1.26±0.28 (PSY) & 3.12±0.54/2.81±0.50 (OPT) in G, Exp 1/2, respectively. AO-correction decreased image quality out-of-focus (Exp 1) and in B (Exp 2) in 6/10 subjects (PSY) & 7/10 subjects (OPT), with OPT and PSY ratios showing a statisically significant correlation (r=0.801, p<0.05).
The study confirms that for some individuals the presence of HOA makes the eye more immune to defocus, similarly whether this defocus is chromatic (Exp 2) or pure defocus of similar magnitude (Exp 1), with the perceptual findings in general paralleling the optical effect. Neural effects (including those affecting subjective best focus setting) cannot be ruled out in subjects that judged AO-corrected G images as more blurred than those viewed through their native optics.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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