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J. C. He; A Theoretical Study on Contribution of the Posterior Corneal Surface to Wavefront Aberrations of the Eye. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2792.
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The posterior corneal surface has minor contribution to refractive power of the eye, but, its contribution to wavefront aberrations or Zernike aberrations of the eye could be different because the posterior corneal aberrations depend not only on difference of refractive index across the surface but also on local variation of the surface shape. The purpose of this study is to theoretically model contribution of posterior cornea to aberrations of the eye.
A MatLab ray-tracing program was developed to calculate Zernike aberrations in the anterior cornea, the posterior cornea, the lens and the whole eye for four model eyes (two of them with GRIN lens). Aberrations in the posterior cornea were also modeled for various shape factor (Q =-0.6 to 0) and angle kappa of the eye (k = 0 to 20 degree). The posterior corneal aberrations were compared to lens aberrations.
Posterior corneal Zernike aberrations varied from model eye to model eye. When k=0, posterior corneal spherical aberration increases with shape factor Q and compensates up to 22% of the anterior corneal spherical aberration (for one of the model one) when Q reaches to 0. Asymmetrical aberrations in the posterior cornea increase with angle kappa k and compensate up to 59% of the astigmatism, 34% of coma and 37% of trefoil of the anterior cornea. Compared to lens aberrations, the relative amplitude of the posterior corneal aberrations changes with model eye, Q and k values, and it could reach similar amplitude as the lens for astigmatism and more than half for coma.
Posterior cornea plays important role, as the lens, in determining aberrations in the eye, and it could compensate more than half of anterior corneal aberrations although it contributes only about eighth of refractive power of the eye.
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