Astigmatic power calculations for intraocular lenses in the phakic and aphakic eye

PURPOSE: To develop sets of equations employed in the power calculations for toric intraocular lenses (IOLs) in phakic or aphakic astigmatic eyes. METHODS: Mathematical operations to convert from standard toric parameters of sphere, cylinder, and axis to astigmatic decomposition components, and vice versa, are presented. These operations are used to derive equations to calculate the ideal toric IOL power for a phakic or aphakic astigmatic eye, predict the postoperative spectacle correction for a selected toric IOL with power other than the ideal power, and back calculate a parameter to be used to optimize predictability of the calculations based on clinical data. RESULTS: Two numerical examples are provided to show how the equations are used with clinical data. CONCLUSION: The equations developed provide a method to perform toric IOL power calculations and supporting operations of predicted postoperative spectacle refraction and optimization of prediction error for phakic and aphakic eyes with astigmatism.