Impact of Zonular Laxity on the Accuracy of Intraocular Lens Power Calculation Formulas in Cataract Patients With Retinitis Pigmentosa

Purpose To evaluate the performance of 12 intraocular lens (IOL) calculation formulas and investigate the impact of zonular laxity on refractive accuracy in patients with retinitis pigmentosa (RP). Design Retrospective study to compare formulas for IOL selection. Methods The study enrolled patients with RP who underwent phacoemulsification and IOL implantation between December 2018 and November 2025. The prediction accuracy of 12 formulas were evaluated. Preoperative average zonular length (AZL) and the difference between the maximum and minimum of zonular length (AZL (max-min) ) were measured by ultrasound biomicroscopy. Multivariate regression and mediation analysis were conducted to explore the factors associated with prediction error. Result A total of 127 eyes from 104 patients were included. The Cooke K6, BUII, Kane, and EVO 2.0 formulas showed no systematic bias and had lower mean absolute errors (0.50–0.51 D), whereas the Hoffer Q, Hoffer QST, Holladay 1, LISA, SRK/T, and T2 formulas showed myopic shifts (-0.21 to -0.12 D, P < 0.05) and Pearl-DGS displayed a hyperopic shift (0.15D, P = 0.009). AZL was positively correlated with PE (β = 0.328, P = 0.019), mediated by postoperative deepening of the anterior chamber ( P < 0.05). For eyes with AZL ≥ 1.8 mm or AZL (max-min) ≥ 1.0 mm, most formulas showed hyperopic shift and reduced refractive prediction accuracy. Conclusion The Cooke K6, BUII, Kane, and EVO 2.0 formulas showed higher predictive accuracy in patients with RP. As zonular laxity predisposes these eyes to a postoperative hyperopic shift, clinicians should fine-tune the target refraction according to zonular length in these eyes.