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Lucie Sawides, Pablo de Gracia, Carlos Dorronsoro, Michael A. Webster, Susana Marcos; The Eye Is Adapted To The Blur Level Imposed By Its Optical Aberrations. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4769.
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To evaluate whether subjects are naturally adapted to the overall amount of blur produced by their own High Order Aberrations (HOA).
Judgments of perceived blur were measured in 11 subjects to determine for each individual the physical blur level that appeared best focused. A sequence of aberrated images was simulated using 128 different real complex wave aberration patterns from real eyes, for 5-mm pupils. The optical quality of these eyes ranged from almost diffraction-limited (achieved with AO-correction measurements) to high amounts of HOA (from surgical eyes). Optical blur was simulated by convolution of the corresponding PSFs excluding tilt and astigmatism, and adjusting defocus to maximize optical quality. Strehl ratios (SR) ranged from 0.049 to 0.757. Simulated images of a 1.98 deg face were presented on a CRT monitor, and viewed monocularly through an adaptive-optics (AO) deformable mirror that compensates for the subject’s natural aberrations. A Badal system compensated for spherical error. AO-correction and pupil centration were continuously monitored and controlled during the experiment. In a 2AFC task, subjects responded whether the image appeared blurred or sharp, with the blur level varied with the QUEST algorithm to estimate the perceived neutral point.The results were analysed in terms of SR, by comparing the natural SR of the subject with the SR of the image perceived as neutral by the subject.
Subjects’ natural SR (at best focus) ranged from 0.065 to 0.282 (5-mm pupils). We found an excellent correspondence between the image quality perceived as neutral and the retinal image quality produced by the aberrations of the subject, with an average deviation of 0.009 (in terms of SR), and a strong correlation between the blur of the image perceived as neutral and the subject’s own blur (R = 0.93; p<0.001; slope=1.19).
Individuals may have an internal code for blur/sharpness, given by the overall amount of blur produced by their HOA. Although our experiment cannot rule out a fine tuning to the specific orientation of the blur, our results are consistent with an adaptation to the overall blur, regardless of its form.
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