Accuracy of Intraocular Lens Power Calculation Formulas Using Total Keratometry in Eyes With Previous Radial Keratotomy

PURPOSE: To evaluate the performance of intraocular lens (IOL) power calculation using standard keratometry (SK) and total keratometry (TK) in eyes after radial keratotomy (RK) surgery. METHODS: A retrospective, consecutive case series study included 49 patients with cataract (65 eyes) after RK. All implanted IOLs were monofocal in-the-bag lenses. Formulas using SK included American Society of Cataract and Refractive Surgery (ASCRS) average, Barrett True K, double-K modified Holladay 1 formula (DK-Holladay), Emmetropia Verifying Optical formula 2.0 (EVO 2.0), Holladay 1, Holladay 2, PEARL-DGS, and LISA formula for patients with cataract and prior myopic refractive surgery (LISA-MRS). Formulas using TK included Barrett True K-TK, EVO 2.0-TK, Holladay 2-TK, and LISA-MRS-TK. Holladay formulas used both Wang-Koch (Holladay-WK) and Holladay axial length (Holladay-AL) adjustment. The mean prediction error (PE), mean absolute PE (MAE), median absolute error (MedAE), root mean square absolute error (RMSAE), and the percentage of eyes within ±0.25, ±0.50, ±0.75, and ±1.00 diopters (D) of PE were evaluated. RESULTS: In formulas using SK, the LISA-MRS formula exhibited the lowest MAE (0.71 D), lowest MedAE (0.52 D), and highest percentage of eyes within ±0.50 D of PE (49.23%). In formulas using TK, the LISA-MRS-TK formula exhibited the lowest MAE (0.78 D), lowest MedAE (0.48 D), and highest percentage of eyes within ±0.50 D of PE (52.63%). Using TK instead of SK significantly reduced the PE of both the Holladay 2 and LISA-MRS formulas. When AL was 30 mm or greater, the Holladay 1-AL formula exhibited the lowest MAE (0.68 D), lowest MedAE (0.32 D), and the highest percentage of eyes within ±0.50 D of PE (59.09%). CONCLUSIONS: In post-RK eyes, the LISA-MRS formula displayed the highest prediction accuracy. TK could improve the prediction accuracy of the Holladay 2 and LISA-MRS formulas.