Comparative Analysis of Twenty Intraocular Lens Power Calculation Formulas in Medium-Long Eyes

Background/Objectives: The choice of appropriate intraocular lens (IOL) power calculation formulas depends on the axial length of the eye. This study compares the accuracy of twenty formulas in medium-long eyes (24.50-25.99 mm). Methods: Data of patients with medium-long eyes, who underwent uneventful phacoemulsification between January 2018 and September 2023, were retrospectively reviewed. Preoperative IOL power was calculated using the IOLMaster 700 with six formulas: Barrett Universal II, Haigis, Hoffer Q, Holladay 1, Holladay 2, and SRK/T. Three months postoperatively, refraction was measured. Postoperative IOL power calculations were then performed using fourteen additional formulas: Castrop, EVO 2.0, Hoffer QST, K6, Kane, Karmona, Ladas Super Formula AI (LSF AI), Naeser 2, Olsen (OLCR), Olsen (standalone), PEARL-DGS, T2, VRF CMAL, and VRF-G. The main outcome measures included standard deviation (SD) of the prediction error (PE) and the percentage of eyes with PE within ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D. Results: Ninety-five eyes with axial lengths ranging from 24.52 mm to 25.97 mm were included. SD values among the twenty formulas ranged from 0.179 (SRK/T) to 0.468 (Olsen OLCR). The percentage of eyes with PE within ±0.50 D ranged from 75.79% (Olsen OLCR) to 98.95% (SRK/T). The SRK/T formula, followed by Holladay 1, demonstrated significantly higher accuracy than most other formulas, while Olsen (OLCR) and Castrop were the least accurate. Conclusions: SRK/T provided the highest accuracy in medium-long eyes, with Holladay 1 performing similarly well. All evaluated formulas achieved PE within ±0.50 D in over 74% of cases.