During the preparations for phakic intraocular lens (PIOL) removal and cataract surgery, physicians can use different intraocular lens (IOL) calculation formulas. A retrospective study found that the newer Kane formula or traditional formulas with an adjustment for Wang-Koch axial length (WK AL) had the highest accuracies. These findings were published in the American Journal of Ophthalmology.
Researchers reviewed medical records from patients (N=36) who underwent PIOL removal with phacoemulsification and in-the-bag IOL implantation between 2018 and 2021 at Sun Yat-sen University in China. Anatomical features of eyes were remeasured using image analysis based on an IOLMaster® 700 (ZEISS) exam and these features were used for IOL calculations using the newer formulas Barrett Universal II (BUII); Emmetropia Verifying Optical (EVO); Kane; and Ladas Super Formula (LSF); or older formulas Haigis; Hoffer Q; Holladay 1; and Sanders, Retzlaff, Kraff 3 (SRK/T).
Patients ages were approximately 46.94±8.68 years, 50.0% were men, axial length was 31.43±2.15 mm, PIOL implantation occurred 9.64±3.85 years prior to cataract surgery, preoperative acuity was 0.81±0.41 logMAR, and postoperative was 0.16±0.23 logMAR. Eyes with anterior (n=12) and posterior (n=24) chamber PIOL differed significantly for endothelium cell density (P =.001), anterior chamber depth (P =.007), and axial length (P =.021).
The accuracy measuring the anterior chamber depth was 100% among anterior chamber PIOL eyes and 37.50% among posterior chamber PIOL eyes.
For anterior chamber PIOL eyes, the lowest median absolute prediction errors were from SRK/T with a second linear WK AL adjustment (0.21), Holladay 1 with a nonlinear WK AL adjustment (0.24), and Kane (0.29) formulas. The poorest performing formula was Holladay 1 without an adjustment (median absolute prediction error, 1.55).
For posterior chamber PIOL eyes, the lowest median absolute prediction errors were Holladay 1 with a second linear WK AL adjustment (0.29), Holladay 1 with a first linear WK AL adjustment (0.31), and Haigis with a first linear WK AL adjustment (0.31) formulas. The poorest performing formula was Hoffer Q without an adjustment (median absolute prediction error, 1.44).
This study was limited by power due to small, imbalanced sample sizes.
The study authors conclude that IOL calculations are influenced by the accuracy of measuring anterior chamber depth. Among newer formulas, the Kane formula had the most accurate prediction in the study and, among the older formulas, any with a WK AL adjustment were most accurate.
Zhang J, Xia Z, Han X, et al. Accuracy of intraocular lens calculation formulas in patients undergoing combined phakic intraocular lens removal and cataract surgery. Am J Ophthalmol. 2021;S0002-9394(21)00506-7. doi:10.1016/j.ajo.2021.09.035