Spherical Equivalent Prediction Analysis In Iol Power Calculations Using Barrett Universal Ii Formula Variations

This study aims to evaluate the predictive accuracy of the Barrett Universal II (BUII) intraocular lens (IOL) power calculation formula in cataract surgery and assess whether incorporating the Sum of Segments (SOS) axial length (AL) method and additional biometric parameters enhances refractive accuracy. By comparing outcomes across short, average, and long eyes, this study seeks to optimize IOL power selection and improve postoperative visual results.

Single-centre academic university hospital.

Retrospective case series of patients who had undergone successful, uneventful cataract surgery. Biometric measurements were obtained using a single swept-source optical biometer. The online analytical tool Eyetemis was used to measure trimmed-means of the spherical equivalent prediction error (SEQ-PE, trueness), precision and absolute SEQ-PE (accuracy). The predictive accuracy of the BUII  formula was assessed using standard biometric parameters, with and without the inclusion of one or two (STD) optional parameters (lens thickness and white-to-white corneal diameter) and the SOS AL (TAL) method. Patients were classified into three groups based on axial length: short (AL < 22.0 mm), average (AL 22.0–24.49 mm), and long (AL ≥ 24.5 mm). 

We included 1340 eyes from 1340 patients. The trimmed-mean SEQ-PE range of all formulas varied from -0.025 to +0.018 Diopters (D). Precision ranged from 0.304 to 0.312 D. Absolute SEQ-PE ranged from 0.303 to 0.312 D. The BUII TAL formula showed the highest precision and accuracy, followed by BUII STD. For short eyes, BUII TAL showed statistically significant better precision and accuracy compared to BUII STD (p<0.01): precision analysis showed a significant advantage for BUII TAL (0.277 D versus 0.309 D), and absolute SEQ-PE further confirmed this superiority, (0.275 D compared to 0.390 D). For average and long eyes, both BUII TAL and BUII STD exhibited strong accuracy, with minimal variation in SEQ-PE and absolute SEQ-PE. 

The prediction accuracy of all BUII formulas was significant. Optimizing the BUII formula with sum-of-segments axial length, followed by the inclusion of optional biometric variables, increased the precision and accuracy of the Barrett Universal II formula outcomes. In particular, for short eyes, the BUII formula optimized for sum-of-segments axial lengths showed the best overall performance. These findings support the adoption of segmented AL measurements in modern IOL power calculations to refine refractive precision and minimize postoperative surprises.