Intraocular lens power calculations in patients with extreme myopia

Purpose: To determine the variables that might contribute to improved intraocular lens (IOL) power calculations preoperatively in cataract patients with extreme myopia. Methods: This retrospective study included 50 patients with extreme myopia and axial lengths longer than 27.0 mm. All patients had clear corneal phacoemulsification by the same surgeon and implantation of the Domilens SiFlex 1 IOL (power range -6.0 to +5.0 diopters [D]). The performances of the SRK/T, Hoffer Q, Holladay 1, and Holladay 2 formulas in predicting an IOL power that would meet the target refraction of +/- 1.00 D were compared. Results: The formulas tended to suggest underpowered IOLs, more severe in eyes with axial lengths greater than 30.00 mm. These eyes accounted for most of the minus-power IOLs implanted, Back calculations of axial lengths in patients with minus-power IOLs showed that, on average, emmetropia could have been predicted by choosing shorter axial lengths (up to 2.72 mm shorter) than those used in the original IOL power calculations. Preoperative B-scan ultrasonography demonstrated the presence of a staphyloma temporal to the optic nerve in several patients who required IOLs, which suggests that axial length measurement problems were a of IOL calculation errors in these patients. Conclusions: In eyes with axial lengths longer than or equal to 27.0 mm, current third- and fourth-generation lens calculation formulas have a tendency to over minus patients between -1.0 and -4.0 D. The formulas appear to perform better for plus-power IOL implantation than for minus-power IOL implantation. The use of B-scan ultrasonography to locate posterior pole staphylomas may improve the accuracy of IOL calculations in eyes with extreme myopia. J Cataract Refract Surg 2000; 26:668-674 (C) 2000 ASCRS and ESCRS.