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J.S. McLellan, S. Marcos, S.A. Burns; Wave Aberrations Are Not Random: Evidence from Pre- and Post-Surgical Wavefronts . Invest. Ophthalmol. Vis. Sci. 2003;44(13):997.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have previously shown that the eye’s measured wave aberrations (expressed as Zernike coefficients) generally produce better modulation transfer functions (MTFs) than do simulated sets of aberrations that have the same RMS error but randomized signs or orientations. The relative advantage of the real aberrations over randomized aberrations is greatest for frequencies near 10 cpd. The current work further investigates these results by comparing real aberrations to randomized aberrations before and after refractive surgery. If the eye’s natural aberrations are non-random, then refractive surgery, which changes the aberrations, might reduce the observed benefit to the MTF. Methods: Total wave aberrations and corneal wave aberrations were measured in 14 myopic eyes (ranging from -2.5 to -13 D) before and after Lasik surgery. Total aberrations were measured using laser ray tracing; corneal aberrations were measured with a standard commercial corneal topographer and custom software. Data were fit with Zernike polynomials through the seventh order. 50 simulated aberration sets were produced by randomizing the signs of each eye’s actual aberrations, while maintaining the RMS error for each term. MTFs were calculated for actual and simulated aberrations, and the actual MTFs were compared to the distribution of MTFs from the simulations. Results: Results are summarized by the MTF Ratio: real MTF / mean MTF of distribution. Pre-surgical total aberrations show an effect similar to previous results: the MTF ratio was significantly > 1.0 at 10 cpd. However, post-surgical aberrations did not show a significant difference. MTF ratios for corneal aberrations were never > 1.0. Conclusions: The current results provide further evidence that the eye’s aberrations are not random. The eye’s optical quality is better than would be expected for random sets of aberrations with the same total RMS error. The fact that this effect is reduced in post-surgical eyes and does not occur for corneal aberrations alone suggests that the eye’s total aberrations may be the result of an active developmental process.
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