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S. Ravikumar, A. Bradley, L.N. Thibos; Do Monochromatic Aberrations Protect The Eye Against Chromatic Blur? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1505.
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Campbell and Gubisch (1967) and later McClellan et al (2002) both report that significant levels of monochromatic aberrations effectively reduce or eliminate the impact of ocular chromatic aberration. This study specifically tests the hypothesis that "Imperfect (aberrated) optics protects the eye against chromatic blur."
Using polychromatic computational optics, we examine the impact of differing levels of monochromatic aberrations on the quality of polychromatic retinal images. A variety of colored objects and illuminants were employed, as well as a wide range of image quality metrics (including Point Spread Function metrics and both Modulation and Optical Transfer Function metrics). Through focus computations are used to identify the optimal refraction, optimal image quality, and depth of focus.
After adjusting spherical defocus to optimize image quality (IQ), normal levels of chromatic aberrations (CAs) alone or monochromatic aberrations (MAs) alone can both drastically reduce image quality relative to the diffraction limit (their relative significance depends on the metric of image quality being assessed). However, when adding MA to the effects of CA or vice versa, only minor additional IQ decrements ensue. Increasing levels of MAs do reduce the impact of chromatic blur, but this effect varies with IQ metric. In the presence of atypically high levels of monochromatic aberrations, the impact of chromatic blur on polychromatic image quality can be almost eliminated, as indicated in McLellan et al. Optimal refraction, although influenced slightly by normal levels of spherical aberrations, is affected more by the interaction between chromatic aberration and source spectrum. Metrics (e. g Area OTF) that take into account the effect of phase–changes estimate polychromatic image quality to be lower than that predicted by Area under Modulation Transfer Function alone.
Although we find that typical levels of monochromatic aberrations can reduce the impact of ocular chromatic aberrations, their effect is small. While high levels of monochromatic aberrations can effectively eliminate any significant impact of CA on optimal polychromatic image quality, CA can still have a significant effect on image quality because of its impact on optimal refraction.
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