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Stephen A. Burns, Anna Leonova, James S. McLellan, Remy Tumbar; Towards comparison metrics for general vision. Journal of Vision 2004;4(11):45. doi: https://doi.org/10.1167/4.11.45.
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There has been a great deal of progress in recent years towards generating metrics for understanding the relation between wave aberrations of the eye and the subjective best refraction of the eye. These metrics have the goal of determining the best refraction, but are less suited to comparing the possible real world performance across eyes, and especially for comparing the potential outcomes of specific “customized” optical corrections. While there are metrics such as the Shannon Number which allow specific comparison of optical information for an imaging system, these describe a best case scenario (optimal focus, etc), so they are not appropriate for the eye under most natural viewing conditions in which information must be extracted over a range of distances and defocus conditions. We compared both real and idealized optical systems based on the in-focus mtf, the depth of focus, and the integrated response of model eyes to 1/f spatial content. While a diffraction limited optical system has a better in-focus Optical Transfer Function, the aberrations of the human eye improve performance out of the plane of focus. Decreasing the aberrations allows the integrated metric to be optimized. For instance, increasing the spherical aberration, by increasing the depth of field, can increase the total focal/frequency volume. Simulations and work in other areas of optics also support the idea that shifts in chromatic content with distance can also be decreased in the same way.
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