Accuracy of intraocular lens calculation formulas in aphakic eyes undergoing simultaneous silicone oil removal and intraocular lens implantation

PURPOSE: To evaluate the accuracy of intraocular lens (IOL) power calculation formulas in aphakic eyes undergoing simultaneous silicone oil removal (SOR) and IOL implantation, including in-the-bag implantation and ciliary sulcus implantation, and assess the effect of 'Rule of 9s' adjustment for ciliary sulcus implantation. METHODS: The performance of six formulas (BUII, EVO, LSF, Hoffer Q, Holladay 1, SRK/T) was evaluated. Outcomes were assessed using mean prediction error (ME) for trueness, standard deviation (SD) for precision, and median absolute error (MedAE) for accuracy. Ciliary sulcus implantation was analysed with and without the 'Rule of 9s' adjustment. RESULTS: This study included 282 eyes (143 in-the-bag, 139 sulcus). For in-the-bag implantation, new-generation formulas (EVO, LSF, BUII) demonstrated higher precision (SD: 0.58 D) and accuracy (MedAE: 0.46-0.47 D) compared to traditional formulas (SD: 0.62-0.71 D; MedAE: 0.50-0.62 D; p < 0.05). Unadjusted sulcus implantation showed low trueness with a significant myopic shift (ME: -0.88 D to -1.12 D). The 'Rule of 9s' adjustment significantly improved trueness (ME: -0.32 D to -0.54 D). Post-adjustment, EVO achieved the best accuracy (MedAE: 0.53 D), significantly better than traditional formulas. CONCLUSIONS: New-generation formulas provide improved precision and accuracy in combined SOR-IOL surgery. The 'Rule of 9s' adjustment optimized trueness for sulcus-placed IOLs, where new-generation formulas maintained higher accuracy and precision.