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A.M. Mahmoud, C. Roberts, D. Castellano, R.G. Lembach; The Impact of Zernike Order in Representing Spherical Aberrations After LASIK . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2548.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Corneal topography following laser refractive surgery is characterized by increased peripheral curvature which results in increased spherical aberration in the optical wavefront. This study investigates the relationship of Zernike order to the reconstruction of curvature profiles after refractive surgery. Methods: A retrospective study of 120 eyes of 60 patients who received Keratron Scout corneal topography (Optikon, Rome, Italy) pre-operatively and one month post-LASIK using one of three lasers, was conducted. Three Zernike decompositions were performed, 5th order, 6th order, and 8th order, and then the surfaces reconstructed from the resulting polynomials. Curvature was calculated along the horizontal meridian for each set of polynomials and compared to the original curvature profile. Results: The 6th order spherical aberration term increased by an order of magnitude from the pre-op to the one month post-op topographic exam. The curvature profiles reconstructed from 5th order Zernike decompositions demonstrated dioptric errors at the peak of the "red ring" in the periphery up to and exceeding 4 D. Conclusions: Although a 5th order Zernike decomposition may be adequate to represent optical aberrations pre-operatively, it is inadequate to represent the magnitude of spherical aberration induced after LASIK, as measured by the topographic changes. However, spherical aberration after refractive surgery is usually reported as the magnitude of a single 4th order term. The 6th order spherical aberration term is necessary to adequately represent the topographic shape changes induced, which generate spherical aberration in the optical wavefront post-operatively.
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