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J. Schwiegerling; Wavefront Aberrations Measurement Incorporating the Stiles-Crawford Effect . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2572.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The Stiles-Crawford effect reduces the effect of aberrations for large pupil sizes. This investigation describes a simple technique for incorporating the Stiles-Crawford effect into conventional wavefront aberration measurements. Methods: Traditionally, wavefront aberration data is expanded into a set of Zernike polynomials. The expansion coefficients describe the weights of different types of aberrations such as defocus, astigmatism, spherical aberration, coma and trefoil. The squares of the coefficients describe the wavefront variance contribution of each aberration type for a uniform circular pupil. The Stiles-Crawford effect, however, reduces the effects of aberrations at the edge of the pupil. Our approach to incorporate the Stiles-Crawford effect into wavefront measurements is to expand the aberration data into a set of Zernike-Gauss polynomials. This new polynomial set has a gaussian weighting over the pupil that can be adjusted to mimic the Stiles-Crawford effect. To test the validity of this technique, we compare the wavefront variance predicted from the Zernike-Gauss polynomials and the number of letters lost by subjects viewing a blurred eye chart. The chart was blurred with equal magnitudes of different types of aberrations. Results: Since equal amounts of aberrations were used to blur the eye charts, wavefront variance from traditional Zernike polynomials would predict equal degradation of visual performance. However, clinically there is a strong dependence of letters lost on the type of aberration present. A strong linear correlation (R2 = 71.2%) was found between the number of letters lost by the subjects and the wavefront variance predicted with the new Zernike-Gauss polynomials. This correlation suggests that this metric would be useful to understand the effects of different types of aberrations on visual performance. Finally, a set of simple conversions have been derived to allow conversion from the traditional Zernike polynomials to the Zernike-Gauss polynomials. The expressions allow the new metric to be rapidly calculated from existing wavefront devices without extensive modifications to their algorithms. Conclusions: The incorporation of the Stiles-Crawford effect into wavefront aberration data provides a metric that correlates well with visual performance.
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