Intraocular lens power calculation and optimized constants for highly myopic eyes.

PURPOSE To determine the accuracy of intraocular lens (IOL) power calculations in eyes with high myopia and to suggest adjusted constants for these cases. SETTING Centre for Ophthalmology, Eberhard-Karls-University, Tuebingen, Germany. METHODS Patients with high myopia having phacoemulsification with implantation of an AcrySof MA60MA IOL (power range +5.00 to -5.00 diopters [D]) were evaluated. Optical biometry (IOLMaster) and IOL calculations were performed before and after IOL implantation. Because of different optic principal planes of negative-diopter and positive-diopter IOLs, separate constants were calculated for these groups. RESULTS Fifty eyes (32 patients) were evaluated. Thirty eyes (mean AL 31.15 mm +/- 1.69 [SD]) had implantation of a positive-diopter IOL (mean power +3.10 +/- 1.50 D) and 18 eyes (mean AL 33.20 +/- 2.25 mm), a negative-diopter IOL (mean power -3.20 +/- 1.70 D). Postoperatively, the mean spherical equivalent was -1.42 +/- 1.33 D and -0.41 +/- 1.81 D, respectively. The difference in optimized constants between positive- and negative-diopter IOLs was significant for all formulas. Power calculation with the SRK II formula showed a wide range of deviation of postoperative refraction from target refraction. Calculation with the Haigis, SRK/T, Holladay 1, and Hoffer Q formulas showed a mean deviation of 0.00 D with an SD of 0.88, 0.92, 1.03, and 1.15, respectively. CONCLUSIONS Results indicate that the SRK II formula cannot be recommended for IOL power calculation in highly myopic patients. With optimized constants, the SRK/T, Haigis, Hoffer Q, and Holladay 1 formulas produced small deviation of postoperative refraction from target refraction.