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Fuensanta A Vera-Diaz, CARLES OTERO MOLINS, Peter J. Bex; Effect of monochromatic aberrations on suprathreshold and threshold discrimination tasks. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1280.
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© ARVO (1962-2015); The Authors (2016-present)
Each form of optical aberration degrades retinal image quality differently, which may be critical for assessing image quality for optical correction and refractive error etiology. We therefore evaluated the effect of different levels and combinations of aberrations on suprathreshold and threshold visual discrimination.
Images were computationally convolved with different combinations of monochromatic aberrations at levels 0.1 to 0.5µm: defocus (C2,0), spherical aberration (SA) (C4,0), vertical astigmatism (C2,2), and oblique astigmatism (C2,-2); or one of these combinations: (C2,2)+ (C2,0), (C2,-2)+ (C2,0), (C2,0)+ (C4,0), all in random order. Aberrations were applied to the images’ point spread functions for a 5mm pupil. Two visual tasks were performed at 5m distance: (1) an ETDRS letter acuity (VA) threshold task, and (2) a suprathreshold task where subjects matched the blur of dead-leaves naturalistic stimuli. Seven healthy subjects with best corrected VA of 0.0LogMAR or better participated. For each visual task and subject, a linear fit was computed and the area under the curve obtained integrating over the range [0.1 0.5] µm.
Repeated measures ANOVA for both tasks showed statistically significant effects among types of aberrations (VA: F=74.70, p<.001, Matching: F=93.07, p<.001). Reduction in VA was greater with defocus and SA than oblique astigmatism (C2,0 - C2,-2: p<0.01; C4,0 - C2,-2: p<0.01). Combinations of aberrations decrease VA less than any single aberration (F=213.96, p<.001). This effect was greater for defocus added to astigmatism than defocus added to SA. For the matching task, oblique astigmatism produced perceptually higher levels of blur compared to the other single aberrations (p<0.01). The perceived blur caused by any single aberration was greater than the combinations of aberrations. Similarly, defocus added to SA was perceived as less blurred when compared to defocus than when compared to SA (p<0.01).
Even though the optical quality of the retinal image varies with aberration order, functional measures of perceived blur and VA are relatively invariant of aberration order. For both matching suprathreshold and threshold discrimination tasks, single aberrations caused greater functional degradation than combinations of aberrations, suggesting that aberrations are not linearly summed in the human visual system.
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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