Abstract: A method of determining a target IOL based on an optimized IOL constant, including, with a computing device, sorting available refraction data from a plurality of cataract surgery patients to identify appropriate post-operative refraction results based on user configurable criteria. Then, for each identified appropriate post-operative refraction result, the method determines a reference IOL constant that would have given an exact desired result for a selected IOL power estimation formula and analyzing the reference IOL constants to provide at least one optimized IOL constant that is: sub-grouped according to an axial length for the selected IOL power estimation formula; or determined as a function of axial length. The computing device determines based on the at least one optimized IOL constant, a target IOL power for a target axial length and target IOL power estimation formula; and provides, based on the target IOL power, a target IOL implant.