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Howard C. Howland; A subjective method for the measurement of monochromatic aberrations of the eye. Journal of Vision 2009;9(14):2. doi: 10.1167/9.14.2.
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© ARVO (1962-2015); The Authors (2016-present)
This paper grew from my brother Bradford's efforts to evaluate the optical quality of his photographic lenses with a crossed-cylinder aberroscope (B. Howland, 1968, Appl. Opt. 7, 1587-1599). We had earlier worked together on a photographic method for refracting the eye and decided to use his crossed-cylinder method to measure the monochromatic aberrations of eyes. We expanded on his method by devising a scheme for extracting the Zernike polynomials up to the fourth order from subjects' drawings of the appearance of the aberroscope shadowed grid on their retinas. We computed the coefficients of the terms of a Taylor polynomial from deflections of the intersections of grid drawings from a best-fitted, uniform grid. We designed and used polynomials that were orthogonal on a 4×4 or 5×5 grid. We integrated the Taylor polynomials to find the Taylor approximation of the wave aberration, and then found the equivalent coefficients for a corresponding Zernike polynomial. The major results of the study were: 1) there was almost a factor of 10 between the rms wavefront aberrationa of the 55 eyes we examined. 2) the major aberration of the eye came from the 3rd order coma-like terms, not the spherical aberration terms as had been assumed earlier, and 3) The values of all the nine 3rd and 4th order Zernike terms contributed significantly to the wave aberration of the eye. To my knowledge, ours was the first measurement of coma in human eyes and the first expression of the monochromatic aberrations of eyes in terms of two dimensional polynomials of any sort.
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