Intraocular lens power calculations in patients with extreme myopia

Purpose: To determine the variables that might contribute to improved intra ocular lens (IOL) power calculations preoperatively in cataract patients wi th 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 phaco emulsification 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 e yes 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 p atients with minus-power IOLs showed that, on average, emmetropia could hav e 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 axia l length measurement problems were a of IOL calculation errors in these pat ients. Conclusions: In eyes with axial lengths longer than or equal to 27.0 mm, cu rrent third- and fourth-generation lens calculation formulas have a tendenc y to over minus patients between -1.0 and -4.0 D. The formulas appear to pe rform better for plus-power IOL implantation than for minus-power IOL impla ntation. The use of B-scan ultrasonography to locate posterior pole staphyl omas may improve the accuracy of IOL calculations in eyes with extreme myop ia. J Cataract Refract Surg 2000; 26:668-674 (C) 2000 ASCRS and ESCRS.