Theoretical image performance with customized aspheric and spherical IOLs – when do we get a benefit from customized aspheric design?

Abstract

Background & PurposeImplantation of an artificial intraocular lens (IOL) during cataract surgery significantly changes the balance of aberrations in the eye. We demonstrate the theoretical superiority of customized aspheric IOL designs over standard spherical IOLs for different values of corneal curvature, asphericity and axial length. MethodsFor a selected set of corneal surfaces we calculated a best-fit equiconvex spherical IOL. In a second step we customized the IOL back surface to correct the wavefront aberrations of the cornea. Then we calculated a quadric approximation of the IOL back surface to retrieve the aspheric parameters of the customized lens in terms of radius of curvature and asphericity/conic constant. The optical performance of the three IOL models was monitored in terms of lateral ray spread (LRS) at retinal plane for variations of corneal curvatures, asphericity and axial lengths of the pseudophakic eye. ResultsThe LRS of customized aspheric IOLs was significantly smaller compared to that of spherical IOLs (typically between 10 and 25dB). For high aspheric coefficients the LRS increased with spherical IOLs. With aspheric IOLs LRS was higher for steep corneas paired with high aspheric coefficients, mostly due to the fitting error of the quadratic function. For several combinations of corneal curvature and aspheric coefficients the focal point of the aspheric IOL was up to 400 times smaller than the spherical one. ConclusionThis study appeals to the reader for the potential benefit of customized aspheric IOL design instead of the principle of a ‘one size fits all’ aspheric coefficient as used currently in clinical practice. A benefit with customized IOLs is less depending from the axial length and can be achieved with corneas of a moderate prolate aspheric shape with an equal or more negative Q value than the average of -0.22. Longer eyes seem to benefit less than short eyes.