Authors: Austin Pereira, Marko Popovic, John C. Lloyd, Sherif El-Defrawy, John Gorfinkel, Matthew B. Schlenker

Purpose: The aim of this study was to evaluate the accuracy of 10 intraocular lens (IOL) power formulas (Barrett Universal II, Haigis, Hill-RBF, Hoffer Q, Holladay 1, Holladay 2, Olsen, SRK/T, Super Formula and T2) in a single, large-sample analysis. 

Study Design: Retrospective consecutive case series. 

Methods: Cataract extraction and IOL implantation procedures between January 2015 - August 2017 from two surgical centres in Toronto, Canada were considered for inclusion. Preoperative biometric estimates were obtained from an IOLMaster 500. The postoperative predicted spherical equivalent was compared to the observed 1-month spherical equivalent for ten IOL power formulas. For five formulas (Haigis, Hoffer Q, Holladay 1, Holladay 2 and SRK/T), and only in eyes > 25.5mm, the Wang-Koch axial length (AL) adjustment was investigated. The primary outcome was the percentage of cases with a prediction error within ±0.50D of target. Secondary analyses investigated the effect of AL and anterior chamber depth on mean prediction error, as well as the percentage of cases with a prediction error within ±0.25D and ±1.00D. 

Results: In decreasing order, the formulas with the highest percentage of cases within ±0.50D of target were: Barrett Universal II (77.4%), T2 (76.4%), Super (75.9%), Holladay 1 (75.4%), Hill-RBF (74.7%), SRK/T (72.6%), Hoffer Q (72.5%), Haigis (71.7%), Olsen (67.4%) and Holladay 2 (67.3%). For short eyes (AL < 22.5mm, n = 69), the Holladay 1 formula proved to be the most accurate (78.3%), whereas the Olsen formula was the least (56.5%). For long eyes (AL > 25.5mm, n = 116), the Barrett Universal II was the most accurate (76.7%), whereas the Olsen formula was the least (62.1%). The Wang-Koch AL adjustment resulted in a shift from hyperopic error to a myopic refractive outcome for all five optimized calculations in cases with long ALs. 

Conclusions: The Barrett Universal II IOL power formula was associated with the most accurate refractive outcome at intermediate and long ALs, whereas the Holladay 1 formula performed best for eyes with short ALs. The Wang-Koch adjustment should be implemented in older generation formulae for eyes with long ALs to improve refractive outcomes.