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X. Cheng, A. Bradley, L.N. Thibos, S. Ravikumar; Visual Impact of Monochromatic Aberrations . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2123.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Our aim was to understand the visual impact of individual Zernike aberrations and combinations of aberrations on spatial vision. Methods: Following Applegate et al 2002, we used wave optics theory to compute and display aberrated images of tumbling-E and Sloan letters. Unlike Applegate et al, these stimuli were displayed on a high luminance, monochromatic, projection monitor after fully compensating for the display non-linearities and display MTF as well as the observer’s OTF. Psychometric functions for character recognition were used to assess the impact of aberrations (every single Zernike aberration modes from the 2nd to the 4th order, and selected combination of 2nd and 4th order Zernike modes) on spatial resolution. Results: Confirming Applegate et al 2002, aberrations with low meridional frequencies (e.g. Z2\0, Z4\0) were always more detrimental than aberrations with higher meridional frequencies (Z4\4, Z3\3), but the relationship was non-monotonic. Adding lower order aberrations to create paraxial focus has the seemingly paradoxical effect of increasing RMS but improving vision. We formally examined the ability of RMS, paraxial image quality and 22 other metrics of image quality to predict the visual impact of monochromatic aberrations. Overall, visual Strehl ratio was the best predictor of visual acuity. Image plane metrics were better predictors than wavefront metrics. Of these, PSF metrics that ignore the low intensity tails (e.g. weighting the PSF with a bivariate Gaussian and integrating, and PSF equivalent width (arcmin) of maximum intensity) gave the highest prediction. Results indicate that RMS (which weights all points in the pupil equally) is a poor predictor of the visual impact of monochromatic aberrations, but levels of aberration in the paraxial region seem much more important. The best pupil-plane metric was pupil fraction, defined as the fraction of the pupil area for which wavefront error is small (i.e. RMS < wavelength/4). Conclusions: These results suggest that strategies to correct monochromatic aberrations that are biased to optimize paraxial optics should render better results than those designed to minimize RMS across the entire pupil.
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