Development and Clinical Accuracy of a New Intraocular Lens Power Formula (VRF) Compared to Other Formulas

Abstract

Purpose: To develop and compare the accuracy and reproducibility of the VRF intraocular lens (IOL) power calculation formula with well-known methods.

Design: Development and validation study.

Methods: This analysis comprised 823 eyes of 823 patients at Kiev Clinical Ophthalmology Hospital Eye Microsurgery Center, Kiev, Ukraine, operated on by 1 surgeon with 3 different types of hydrophobic lenses: IQ SN60WF (494 eyes) and ReSTOR SN6AD1 (169 eyes) (Alcon Labs, Fort Worth, Texas, USA) and AMO Tecnis MF ZMB00 (160 eyes) (J&J Vision, Santa Ana, California, USA). The full data set was divided into 2 subsets, the first to develop the new formula and the second to evaluate their performance with other most commonly used modern methods of IOL power calculation (Haigis, Hoffer Q, Holladay 1, Holladay 2, SRK/T, and T2). The VRF algorithm is empirical; it uses 4 predictors for estimation of postoperative lens position, including axial length, corneal power (K), preoperative anterior chamber depth (corneal epithelium to lens), and horizontal corneal diameter. The results are also stratified into groups of short (≤22 mm), medium (>22 to <24.5 mm), medium-long (≥24.5 to <26 mm), and long (≥26 mm) axial length.

Results: The mean error, median absolute error, and mean absolute error were evaluated for all 7 methods with 1 IOL type. The VRF formula had the lowest median (0.305 diopter [D]) absolute error over the entire axial length range, and was comparable with the formulas for T2 (0.321 D) and Holladay 1 (0.326 D).

Conclusion: The new formula was comparable with well-known methods and was better over the entire axial length range.