Development and Validation of a new Formula for Intraocular Lens Power Calculation in Patients with Myopic Corneal Refractive Surgery

Purpose: To develop and validate a new intraocular lens (IOL) power calculation formula for cataract patients with previous myopic corneal refractive surgery (MRS).Design: Retrospective, comparative analysis of lOL power calculations.Participants: Patients undergoing MRS were enrolled for formula development, and cataract patients with prior MRS were recruited for evaluation.Methods: Linear regression model was used to characterize the relationship between preoperative anterior corneal radius (ARC) and postoperative posterior corneal radius (PRC) in patients undergoing MRS.A thick-lens LISA MRS formula was then developed, using predicted preoperative ARC for effective lens position estimation.Its performance was compared with existing formulas (Barrett True K, Emmetropia Verifying Optical [EVO], Haigis-L, Hoffer QST, and Shammas PL) in cataract patients with prior MRS.Main Outcome Measures: Arithmetic and absolute prediction errors.Results: The study included 134 MRS patients (98 small incision lenticule extraction [SMILE] and 36 femtosecond laser-assisted in situ keratomileusis [FS-LASIK]) for formula development, and the changes in anterior and posterior keratometry were comparable between the two procedures.Postoperative PK was a strong predictor of preoperative ARC, with an R 2 of 0.82.In 225 cataract patients from three centers for formula validation, the formula performance index (FPI) was highest for LISA MRS (with or without PRC, 0.43), followed by Hoffer QST (0.37), EVO and Hoffer QST-PRC (both 0.32), EVO-PRC and Barrett True K-PRC (both 0.30), and Barrett True K (0.26).LISA MRS-PRC and EVO-PRC yielded the lowest median absolute prediction error (0.47 D), with EVO-PRC performing relatively better in eyes with AL < 28 mm and LISA MRS-PRC maintaining favorable accuracy in eyes with AL 28 mm.Incorporating PRC significantly improved the performance of Barrett True K, LISA MRS, and Hoffer QST (all P< 0.05). Conclusions:The LISA MRS formula provides accurate IOL power calculation for cataract patients with prior MRS, particularly in eyes with AL 28 mm.Use of PRC is recommended whenever available.