Accuracy of sixteen axial length adjusted intraocular lens power calculation formulas in long Caucasian eyes

To compare the accuracy of sixteen intraocular lens (IOL) power calculation formulas incorporating targeted adjustments or regression-based modifications of axial length (AL) in eyes longer than 26.00 mm. Retrospective observational study. The data of myopic patients with cataract who underwent uneventful phacoemulsification with in-the-bag implantation of a PARTIAL−RoF narrow IOL between January 2020 and June 2025 were reviewed. Preoperative IOL power was calculated using the IOLMaster 700 with six formulas: Barrett Universal II (BU II), Haigis, Hoffer Q, Holladay 1, Holladay 2, and SRK/T. The implanted IOL power was selected from BU II or SRK/T recommendations. Refraction was measured three months postoperatively. Postoperative IOL power predictions were generated using the following formulas or formula variants: K6, PEARL-DGS, Castrop, Eom, VRF CMAL; Holladay 1 with Wang-Koch 2 center optimization (WK2), modified Wang-Koch (MWK), non-linear regression (NLR), and Fam-adjusted method (F2); SRK/T WK2, SRK/T MWK, SRK/T F2; Holladay 2 NLR; Hoffer Q WK2; Haigis WK2; and Barrett True AL. The primary outcome measures were root mean square absolute error (RMSAE) and the percentage of eyes with prediction error (PE) within ± 0.25 D, ± 0.50 D, ± 0.75 D, and ± 1.00 D. One hundred sixty-four eyes with ALs ranging from 26.04 mm to 29.72 mm were included. RMSAE values across the sixteen formulas ranged from 0.393 (Holladay 1 NLR and SRK/T WK2) to 0.803 (Haigis WK2). The percentage of eyes with PE within ±0.50 D ranged from 35.98% (Haigis WK2) to 81.1% (Holladay 1 NLR). Holladay 1 NLR—followed by SRK/T WK2, Holladay 1 MWK, VRF CMAL, PEARL-DGS, and Eom—demonstrated significantly higher accuracy than most other formulas. Haigis WK2 and Hoffer Q WK2 were the least accurate. Certain modified third-generation formulas (Holladay 1 NLR, SRK/T WK2) achieve accuracy comparable to that of new-generation formulas (PEARL-DGS, K6, VRF CMAL) in IOL power calculations for long eyes. However, some third- and fourth-generation formulas—even after AL-based modification (Hoffer Q WK2, Haigis WK2)—continue to yield suboptimal results in this anatomical range.