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James S. McLellan; Wave aberrations protect the eye against chromatic blur. Journal of Vision 2002;2(10):109. doi: 10.1167/2.10.109.
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The optics of the eye are subject to both chromatic and monochromatic aberrations. The effects of monochromatic aberrations on retinal image quality have been widely studied in recent years, but the interactions among monochromatic aberrations and longitudinal and transverse chromatic aberrations (LCA and TCA, respectively) have received less attention. LCA is a wavelength-dependent change in refractive power of about 2 Diopters across the visible spectrum. Conventional wisdom has long held that when the eye is focused for mid-spectral light, LCA blurs short-wavelength light so much that it can contribute little to spatial vision. This assumption has been used to explain both the presence of macular pigment and the sparse mosaic of S-cones in the retina. To investigate the combined effects of all the eye's aberrations, we measured monochromatic wavefronts at multiple wavelengths from 450 to 650 nm, and computed polychromatic point spread functions and modulation transfer functions (MTFs). Results show that when the effects of all aberrations are taken into account, retinal image quality, as measured by the MTF, is roughly constant across the visible spectrum. Monochromatic aberrations degrade MTFs for mid-spectral wavelengths but actually improve MTFs for the spectral extremes, thereby decreasing the variability in image quality with wavelength that would be expected from LCA alone. Consequently, the potential MTF for the S-cones is comparable to that for L- and M-cones, and the presence of macular pigment has little effect on retinal image quality.
McLellan J.S., Marcos S., Prieto P.M., Burns S.A. (2002). Imperfect optics may be the eye's defence against chromatic blur. Nature 417, 174–176.
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