Comparison of Three Formulas for Intraocular Lens Power Formula Accuracy

Abstract

Purpose: To compare the accuracy of three intraocular lens (IOL) power calculation formulas (SRK/T, Barrett Universal II, and T2) in cataract surgery patients. Methods: In total, 73 eyes of 73 patients who underwent uneventful cataract surgery were retrospectively reviewed. IOL power was determined using SRK/T, Barrett Universal II, and T2 preoperatively. The findings were compared with the actual refractive outcome to obtain the prediction error. The mean prediction error (ME) and mean absolute error (MAE) of each formula were compared. The MAE was defined as the difference between the postoperative spherical equivalence (SE) and the preoperatively predicted SE. The ME and MAE of each formula 3 months after surgery were compared with preoperatively predicted SE. Eyes were classified into subgroups based on axial length (AL) and average keratometry (K). Results: The ME and MAE for the three formulas were SRK/T [-0.08 +/- 0.45 diopters (D) and 0.35 +/- 0.40 D, respectively], Barrett Universal II (-0.01 +/- 0.44 D and 0.33 +/- 0.30 D, respectively), and T2 (0.04 +/- 0.45 D and -0.34 +/- 0.30 D, respectively), but no statistically significant differences were detected. Similar results were obtained in groups with a long AL or a large average K. In groups with an AL >= 26 mm or with an average K >= 47 D, the Barrett Universal II formula yielded the smallest standard deviation and a ME closest to zero, but these differences were not statistically significant. Conclusions: No significant differences were observed between the three formulas regarding ME or MAE. However, recent formulas such as the Barrett Universal II could provide certain benefits in predicting IOL power for patients with a long AL (> 26 mm) or larger average K. Further research with a larger sample size is recommended for more evaluation.