Spherical Equivalent Prediction Analysis in IOL Power Calculations using Barrett Universal II Formula Variations

Purpose: To evaluate the prediction accuracy of the Barrett Universal II (BUII) intraocular lens (IOL) formula variations, including optional biometric parameters and sum-of-segments (SOS) axial length (AL) modification, for IOL power calculation in cataract surgery. Setting: Single-center academic university hospital. Design: Retrospective case series. Methods: A total of 1340 eyes of 1340 patients undergoing uneventful cataract surgery were analysed using five BUII variants: with only one optional parameter ([lens thickness (BUII LT) or white-to-white (BUII WTW)], two optional parameters (BUII STD), without optional parameters (BUII WØ), and adjusted for SOS AL (BUII TAL). A single swept-source optical biometer (ARGOS) was used. Spherical equivalent prediction error (SEQ-PE, trueness), standard deviation (SD, precision), and absolute SEQ-PE (accuracy) were calculated with the online Eyetemis tool. Statistical comparisons were conducted using robust statistical methods across the entire cohort and subgroups based on AL: short (<22.0 mm), average (22.0–24.99 mm), and long (≥25.0 mm). Results: All formula variations showed high refractive accuracy. BUII TAL provided superior precision and best accuracy, particularly outperforming other variants in short eyes (p<0.01). For average and long eyes, accuracy and precision differences between the modified BUII TAL and standard BUII STD were minimal and not statistically significant. The percentage of eyes within ±0.50 D prediction error was highest for BUII TAL and BUII STD (80%), slightly outperforming other variants. Conclusions: BUII formula variants demonstrated excellent refractive prediction accuracy. Sum-of-segments adjustment and optional biometric parameters notably improved precision and accuracy, especially in short eyes.