VRF-G, a New Intraocular Lens Power Calculation Formula: A 13-Formulas Comparison Study

PURPOSE: To compare the accuracy of a newly developed intraocular lens (IOL) power formula (VRF-G) with twelve existing formulas (Barret Universal II, EVO 2.0, Haigis, Hill-RBF 2.0, Hoffer Q, Holladay 1, Kane, Næeser 2, PEARL-DGS, SRK/T, T2 and VRF). METHODS: Retrospective case series including 828 patients having uncomplicated cataract surgery with the implantation of a single IOL model (SN60WF). Using optimised constants, refraction prediction error of each formula was calculated for each eye. Subgroup analysis was performed based on the axial length (short ≤22.0mm; medium >22.0mm to <26.0mm; long ≥26.0mm). Main outcomes included mean prediction error (ME) mean (MAE) and median absolute error (MedAE), in diopters (D), and the percentage of eyes within ±0.25D, ±0.50D, ±0.75D and ±1.00D. RESULTS: Formulas absolute errors were statistically different among them (p<0.001), with Kane having the lowest MAE of all formulas, followed by EVO 2.0 and VRF-G, which had the lowest MedAE. The Kane formula had the highest percentage of eyes within ±0.25D (47.0%) and ±1.00D (97.7%) and the VRF-G formula had the highest percentage of eyes within ±0.50D (79.5%). For all AL subgroups, Kane, EVO 2.0 and VRF-G formulas had the most accurate performances (lowest MAE). CONCLUSION: New generation formulas may help us in achieving better refractive results, lowering the variance in accuracy in extreme eyes – Kane, EVO 2.0 and VRF-G formulas are promising candidates to fulfil that goal.