Intraocular lens power formula based on vergence calculation and lens design

Purpose: To present a new method of intraocular lens (IOL) power calculation that takes into account the power-dependent variation in lens design. Setting: Department of Ophthalmology, Aalborg, Denmark. Methods: Information on exact IOL design is derived from the manufacturers' cutting cards. These data were built into an IOL calculation formula based on exact ray tracing and vergence calculation. All algorithms are demonstrated. Results: The method is optically correct as all refractive surfaces are characterized with respect to both position and refractive power. In simulation models, the Naeser and the Holladay formulas performed similarly, while the SRK/T formula predicted higher postoperative refractions for low-power IOLs. Conclusion: It is possible to incorporate the exact IOL design into an IOL power calculation formula. Theoretically, the Naeser formula should increase the accuracy of IOL power calculation; however, this has yet to be proved from empirical data. The formula provides an advantage in analysis of postoperative pseudophakia for experimental/scientific purposes because all intraocular distances and powers may be measured or calculated.