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A.Y. Leonova, J.S. McLellan, S.A. Burns; Variation in transverse chromatic aberration with wavelength . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2835.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The image quality of the eye in polychromatic light depends strongly both on the monochromatic aberrations of the eye, and on the polychromatic aberrations (longitudinal and transverse chromatic aberration). While longitudinal chromatic aberration (LCA) is fairly consistent across observers, transverse chromatic aberration (TCA) varies markedly. To investigate the potential impact of this variability we measured the complete wavefront aberrations of the eye between 430 nm and 670 nm. Methods: The monochromatic wavefront aberrations were measured for 8 wavelengths using a spatially resolved refractometer. Subjects adjusted the incident angle of the test beam at the pupil to align a test spot to a reference stimulus viewed through the pupil center. 37 entrance pupil locations for the test spot were sequentially sampled within the 7mm artificially dilated pupil (in 6 subjects). Low order statistic of the vertical and horizontal angular deviations of the test beam for different entrance pupil locations was employed to estimate LCA and TCA. LCA was computed from the slope of the linear regression fits to the vertical and horizontal angular deviations. The vertical offsets of the fits at x=0 location were used to estimate central pupil optical TCA (oTCA). The linear regression of the wavefront slopes vs position were used as a measure of the defocus. To average across pupil locations the average wavefront slopes as a function of wavelength were computed within different diameter pupils. We also determined the achromatic axis (no differential tilt with wavelength) of the eye for different pairs of wavelengths. Results: The change in the slope of the linear fits with wavelength revealed the classic LCA for all subjects. Optical TCA varied markedly across subjects. oTCA changed with wavelength monotonically, but not linearly. With a steeper increase in horizontal oTCA at short wavelengths, and a shallower increase at long wavelentgths. None of the subjects showed a strong vertical component to the oTCA with wavelength. Average TCA across the pupil was relative constant as pupil size increased from 3, to 5 to 7 mm pupils. The location of the achromatic axis, for different pairs of wavelengths differed somewhat within subjects. Conclusions: In agreement with other studies variations in LCA are relatively small, but there are large individual differences in TCA. A simple linear approximation of displacement vs wavelength is not accurate in predicting the change in horizontal optical TCA with wavelength. This occurs presumably because the dispersion of the eye is not proportional to wavelength. Variation in TCA with pupil size tends to be small.
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