Comparison of Kane, Hill-RBF 2.0, Barrett Universal II, and Emmetropia Verifying Optical Formulas in Eyes With Extreme Myopia

PURPOSE: To compare the accuracy of the Kane, Hill-RBF 2.0, Barrett Universal II (BUII), and Emmetropia Verifying Optical (EVO) formulas in calculating intraocular lens power in extremely myopic eyes. METHODS: A total of 1,054 highly myopic eyes were included and divided into three groups according to axial length: control (⩾ 26 to < 28 mm), long (⩾ 28 to < 30 mm), and extreme axial length (⩾ 30 mm) groups. Prediction accuracies of the four formulas were compared and factors influencing the refractive errors were evaluated. RESULTS: The Hill-RBF 2.0 formula generated the largest percentage of eyes with refractive errors within ±0.50 and ±1.00 D (71.44% and 94.59%, respectively, compared to 63.38% and 92.31% for the Kane, 61.76% and 94.02% for the BUII, and 59.01% and 87.57% for the EVO formulas; P < .001). The mean absolute errors of the Kane, Hill-RBF 2.0, BUII, and EVO formulas were 0.46 ± 0.38, 0.40 ± 0.39, 0.44 ± 0.30, and 0.58 ± 0.68 D ( P < .001). In the long axial length group, the Hill-RBF 2.0 formula had the smallest MAE (all P < .001), whereas the extreme axial length group only had a smaller MAE than the Kane and EVO formulas (both P < .001). The accuracy of the Kane and Hill-RBF 2.0 formulas was affected by corneal curvature and A-constant; the accuracy of the BUII and EVO formulas was affected by corneal curvature, axial length, and A-constant. CONCLUSIONS: The Hill-RBF 2.0 formula outperformed all three other formulas in eyes with axial lengths ⩾ 28 to < 30 mm, and outperformed the Kane and EVO formulas in eyes with axial lengths of 30 mm or greater. [ J Refract Surg . 2021;37(10):680–685.]