Intraocular Lens Calculations after Hyperopic Refractive Surgery

Purpose To evaluate the effect of hyperopic refractive surgery on intraocular lens (IOL) power calculation, compare published methods of IOL power calculation after refractive surgery, evaluate the effect of prerefractive surgery refractive error on IOL deviation, and introduce a new alternative formula for IOL calculation in patients who have had refractive surgery for hyperopia. Design Retrospective noncomparative case series. Participants Twenty eyes from 13 patients who had undergone cataract surgery after previous hyperopic refractive surgery. Methods Seven different methods of IOL calculation were performed retrospectively: clinical history (IOLhisK ), clinical history method at spectacle plane (IOLhisKs ), vertex (IOLvertex ), back calculated (IOLBC ), calculation based on average keratometry (IOLavgK ), calculation based on steepest keratometry (IOLsteepK ), and calculation based on the double K formula (IOLdoubleK ). Each method’s result was compared with an exact IOL (IOLexact ), which would have resulted in emmetropia. Each method was then compared with change in spherical equivalent induced by refractive surgery (SEh ). A paired t test was used to determine statistical significance. Main Outcome Measure Mean error in IOL power prediction for each method when compared to IOLexact. Results When evaluating different methods of IOL calculations, IOLvertex was the most accurate, with a mean deviation from emmetropia of 0.42±1.75 diopters (D), followed by IOLBC (+0.54±1.86 D), IOLhisK (+1.56±2.35 D), IOLhisKs (+1.57±2.35 D), IOLsteepK (+1.59±2.25 D), IOLdoubleK (+1.65±2.56 D), and IOLavgK (+2.24±2.46 D). There was no statistical difference between IOLvertex , IOLBC , and IOLexact . The power of IOLavgK would be inaccurate by 0.27 x +1.53, where x = SEh . Thus, most patients without the adjustment to IOLavgK would be left myopic. However, when IOLavgK is adjusted with this formula, there is no statistical difference to IOLexact. Conclusions For IOL power selection in previously hyperopic patients, a predictive formula based only on SEh and current average keratometry readings was not found to statistically differ from IOLexact . The IOLvertex and IOLBC , which also did not statistically differ from IOLexact , require prerefractive surgery keratometry readings that are often not available to the cataract surgeon.