Spherical aberration for intraocular lenses is calculated based on surface contributions. The impact on image quality can be determined using a defined pupil function. Relationship between wavefront aberration and displacement of the best focal plane is discussed. The impact on ANSI Z80.7 power labelling is computed and found to be as great as 0.9 Diopters for standard lens types from the combination of media conversion error and spherical aberration. A pupil function is defined for solution of the Fresnel diffraction integral, in the Fraunhofer approximation, and is used to compute strehl ratio and modulation transfer function for symmetrical biconvex, convex plano and meniscus lenses in standard atmosphere and in situ. Results in air indicate best optical performance for convex plano lenses due to minimization of spherical aberration. In situ, all lenses analyzed performed approximately equally well. Use of this calculation technique for refractive bifocal IOL performance prediction is discussed.