Comparison of formulas and methods for high myopia patients requiring intraocular lens powers less than six diopters.

Purpose: To determine the best method to minimize postoperative hyperopia and achieve mild myopia in patients requiring low-powered (<6.00 D) MN60MA intraocular lenses (IOLs).
Methods: This retrospective non-comparative case series consists of 32 eyes (20 patients). Postoperative spherical equivalent (SE) refractions were compared using four methods: standard formulas with varying target refractions (Haigis -1.00 D, Hoffer Q -1.75 D, Holladay 1 -1.50 D and SRK/T -1.00 and -1.25 D), axial length adjustment methods for standard formulas targeted for both plano and -0.50 D, Barrett Universal II formula and the Haigis formula using separate constants for plus and minus IOLs (Haigis +/-). SE (mean, standard deviation, median, range), median absolute error (MedAE), prediction errors, percentage SE less than 0.25 D and greater than -1.00 D, percentage SE within ±0.50 and ±1.00 D of the targeted refraction were calculated.
Results: All methods and formulas gave acceptable mean SE refractions ranging from -0.04 to -0.68 D. The Barrett Universal II, Haigis +/-, standard Haigis formula targeted for -1.00 D and the Holladay 1 formula targeted for -1.50 D met stricter criteria of final SE between 0.25 and -1.00 D in 94-100% of eyes and MedAE between 0.37 and 0.51 D. Other methods had more myopic or hyperopic outliers.
Conclusions: For these eyes with high myopia, the Barrett Universal II, Haigis +/-, standard Haigis targeted for -1.00 D and the standard Holladay 1 targeted for -1.50 D formulas produce the best results exceeding established benchmark criteria and minimizing hyperopic surprises.