Prospective evaluation of intraocular lens calculation after myopic refractive surgery

PURPOSE: To evaluate outcome after refractive surgery in cataract patients for whom intraocular lens (IOL) selection was based on the use of a myopic regression formula. METHODS: This prospective case series included 20 eyes of 14 patients who had previous uncomplicated myopic refractive surgery, followed by uncomplicated cataract extraction with IOL implantation. Calculation of IOL was based on flattest keratometry readings, spherical equivalent refraction before refractive surgery, and an adjustment factor derived from the regression formula: -(0.47x + 0.85). Following cataract extraction, refractive error was compared against refractive aim. The power of IOL obtained by the regression formula (IOL_RF) was compared to those obtained using the clinical history method at the spectacle plane (IOL_HisKs) and the Double-K formula (IOL_DoubleK). The results acquired with each technique were compared with those achieved using an IOL back-calculated for emmetropia (IOL_exact). RESULTS: Using the regression formula, IOL calculations produced postoperative cataract extraction refractions within 1.00 diopter (D) (range: -1.00 to 0.78 D) of the intended outcome. Mean spherical equivalent refraction after cataract extraction was -0.31±0.56 D. Twelve of 20 eyes had sufficient data to evaluate the statistical relationships among the three formulas compared with IOL_exact. Paired t test results revealed IOL_RF (P=.0932) and IOL_HisKs (P=.9955) were not statistically different from IOL_exact whereas IOL_DoubleK was statistically different from IOL_exact (P=.0008). CONCLUSIONS: The myopic regression formula is recommended for postoperative myopic LASIK IOL selection to provide a simple, accurate, and consistent method of predicting IOL calculation that is not statistically different from IOL_exact.