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J.T. Schwiegerling; The Effect of Wavefront Misalignment on Visual Performance Predictors . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2767.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To develop simple mathematical relationships to determine the effect of higher order aberrations on lower order terms when the wavefront pattern is decentered or rotated. Methods: New Zernike coefficents can be calculated by performing a Taylor expansion on a decentered wavefront. These new coefficients are dependent upon the degree of decentration and/or rotation of the wavefront and higher order coeffcients from the original wavefront. Results: A general set of expressions for wavefront decentration and rotation through 7th order polynomial fits has been created. The effect of decentration on defocus has been examined and coma, spherical aberration and secondary astigmatism affect the ability to predict spherical equivalent power from a decentered wavefront. For myopic eyes, coma causes a hyperopic shift, while spherical aberration and secondary astigmatism cause a myopic shift for decentered wavefronts. For hyperopic eyes, the effects are reversed. For small decentrations, coma has the dominating effect. For large decentrations spherical aberration has the major effect. Conclusions: Misalignment of the center of the wavefront introduces errors into visual performance metrics derived from Zernike coefficients. The mathematical expressions derived under this work are useful for comparing multiple wavefronts, examining the effects of refractive surgery, aligning corneal topographies and determining tolerances on device alignment.
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