Accuracy of Barrett versus third-generation intraocular lens formula across all axial lengths

Abstract

The purpose of this study is to evaluate and compare the accuracy of Barrett Universal II versus third-generation formula for different intraocular lens (IOL) powers for Indian eyes with different axial lengths (ALs). This is a retrospective, nonrandomized consecutive case series. This study reviewed 981 eyes from 825 patients who had uneventful cataract surgery and IOL implantation. The eyes were separated into subgroups based on AL as follows: short (<22.0 mm), medium (22.01-23.99 mm), and long (>24.0 mm). The predicted refractive outcome using formulas was calculated and compared with the actual refractive outcome to give the prediction error. The percentage of every refractive error absolute value for each formula was calculated at <±0.50D, 0.50D-0.75D, and >±0.75D. In all, 981 eyes were analyzed. There were no significant differences in the median absolute error predicted by Barrett and the third-generation formulae. The Barrett Universal II formula resulted in significantly lowest mean spherical equivalent in short eyes (P = 0.0047) as well as a higher percentage of eyes with prediction errors within <±0.50D, 0.50D-0.75D, and >±0.75D. We found that the Barrett Universal II formula had the lowest predictive refraction error and mean absolute error across all ALs. The Barrett Universal II formula rendered the lowest predictive error compared with SRK/T, Holladay, and Hoffer Q formulas. Thus, the Barrett Universal II formula may be regarded as a more reliable formula for achieving emmetropia and reducing postoperative refractive surprises across all ALs.