Development and Clinical Accuracy of the New Paraxial Ray-Tracing IOL Power Formula (VRT) Based on the Thin Lens Assumption

Purpose: To develop and evaluate the refractive and clinical accuracy of the novel IOL power calculation formula (VRT) in unoperated Caucasian eyes. Methods: This retrospective and single-center study included 1016 eyes of 1016 patients, all operated on by a single surgeon using PARTIAL-RoF narrow IOL (Tecnis 1 ZCB00, Johnson & Johnson Vision, Jacksonville, FL, USA). The complete data set was divided into two groups: the first was used to develop the new formula (489 eyes), and the second—the test group (527 eyes)—was used to assess its performance alongside other formulas (Barrett Universal II (BUII), Haigis, Hoffer Q, Hoffer QST, Holladay 1, Cooke K6, Kane, Norrby RT, Olsen (OLCR), Olsen (standalone), Pearl-DGS, SRK/T, VRF, and VRF CMAL). The VRT formula is based on a paraxial ray-tracing method that employs two constants and the thin-lens assumption. The ELP algorithm was adopted from the VRF formula, incorporating the Cooke-modified axial length (CMAL) correction. Subgroup analysis was also stratified by axial length as follows: short (≤ 22.00 mm), medium (22.01– 25.99 mm), and long (≥ 26.00 mm). Preoperative examination was performed using the SS-OCT biometer (IOLMaster 700; Carl Zeiss Meditec AG). All descriptive statistics were analyzed using optimized lens constants. Results: The VRT formula demonstrated the highest accuracy (SD 0.358 D), outperforming all traditional formulas (Haigis, Hoffer Q, Holladay 1, SRK/T), modern thin lens formulas (VRF), and some ray-tracing methods (Norrby RT, Olsen (OLCR), Olsen (standalone); P < 0.05). Meanwhile, the new formula showed comparable accuracy with modern methods such as BUII, Hoffer QST, Cooke K6, Kane, and Pearl-DGS (P > 0.05). Conclusion: The VRT formula showed promising results, outperformed traditional formulas, and was comparable to modern IOL power calculation methods in Caucasians, using one IOL model, which can be considered a limitation of this study.