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JA Campin, GP Gray, KK Liedel, GH Pettit; Impact of Pupil Aperture, Wavefront Origin and Higher Order Aberrations on the Computation of Sphero-Cylindrical Powers in Measured Wavefronts . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2046.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: One use of wavefront measurement devices is the determination of the classical spherical and cylindrical refractive powers of the eye. Typically, these devices do a good job in determining these parameters in untreated eyes with low levels of higher order aberrations but the results are less satisfactory with post-lasik and other highly aberrated eyes. In this study, analysis and experiments were done to determine the impact of the origin and size of the pupil aperture over which processing is performed and the level and type of higher order aberrations. A new, more sophisticated approach is proposed that improves performance in these cases. Methods: Using the ALCON LADARWave device, a Hartman-Shack wavefront sensor, wavefront measurements were made of untreated eyes, post-lasik eyes and other highly aberrated eyes. Subjective refractions were also performed. The sphero-cylindrical component of the wavefronts was computed in the standard manner by reconstructing the wavefronts about the wavefront center and determining the quadratic components. Agreement between these computations and subjective measurements was assessed. The ability to improve the agreement by changing the origin of the wavefront reconstruction and the aperture of the reconstructed wavefront was demonstrated. The impact of higher order aberrations on the computations was assessed and an optimal methodology for determining the sphero-cylindrical powers proposed. Results: Correlation and agreement between subjective refraction and standard wavefront sphero-cylindrical computations was poor in post-lasik and other highly aberrated eyes but could be significantly improved by using the techniques described here. Conclusion: The dynamics and orientation of human eyes during subjective refractive measurements differ from those during wavefront measurements. Consequently, the origin and diameter of reconstructed wavefronts needs to be addressed along with the higher order aberrations if good agreement to subjective measurements is to be obtained.
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