Purchase this article with an account.
JC He, J Gwiazda; Relationship Between Spherical Aberration in the Lens and Viewing Distance . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1896.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Zernike spherical aberrations in the whole eye recently were reported to be more negative as viewing distance gets closer both for accommodated eyes relative to relaxed eyes (He, et al, Vision Res., 2000) and for myopic eyes (which have a closer far point) relative to emmetropic eyes (He, et al, 2001 OSA Annual Meeting). The more negative Zernike spherical aberrations in the whole eye, however, can not be attributed simply to the lens because corneal spherical aberrations change with viewing distance even without any change in corneal shape. The purpose of this study is to model corneal spherical aberrations for targets at different distances, so that the contribution of spherical aberration from the lens can be calculated. Methods: A MatLab ray-tracing program was developed to calculate wavefront aberration caused by the cornea for targets from -6 D to 0 D, and to analyze spherical aberration by decomposing the wavefront aberration into Zernike functions with orders as high as 20. The coefficient of Z40 was used to estimate the spherical aberration. The vertex curvature of the cornea was assumed to be 7.8 mm, and three asphericities (kappa value) were modeled: -0.393 (Lotmar, 1971), -0.533 (Howland et al, 1994) and -0.535 (ideal cornea for infinity). Results: The corneal Zernike spherical aberration was found to be positive and to increase linearly with decreasing viewing distance in the model. While the Zernike coefficient increased from 0.17 to 0.35 micron (slope = 0.03 micron/D) for Lotmar's cornea as the target changed from -6 D to 0 D, it increased from 0.00 to 0.18 micron (slope equal to 0.03 micron/D) for the other two corneal shapes. Increasing amounts of negative spherical aberration in the lens were required to produce more negative spherical aberrations in the whole eye for both the accommodated and the myopic eyes. Conclusion: More positive spherical aberrations are induced in the cornea as a target gets closer. Therefore, the more negative spherical aberrations in the whole eye can be attributed to the lens for both accommodated and myopic eyes.
This PDF is available to Subscribers Only