Intraocular lens power calculation after corneal refractive surgery: Double-K method

Abstract

Purpose: To determine the accuracy of a method of calculating intraocular lens (IOL) power after corneal refractive surgery. Setting: Department of Ophthalmology, Hospital de Gipuzkoa, San Sebastián, Spain. Methods: The SRK/T formula was modified to use the pre refractive surgery K-value (Kpre) for the effective lens position (ELP) calculation and the post refractive surgery K-value (Kpost) for IOL power calculation by the vergence formula. The Kpre value was obtained by keratometry or topography and the Kpost, by the clinical history method. The formula was assessed in 9 cases of cataract surgery after laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) in which all relevant data were available. Refractive results of the standard SRK/T and the double-K SRK/T were compared statistically. Results: The mean IOL power for emmetropia and the achieved refraction (mean spherical equivalent [SE]), respectively, were +17.85 diopters (D) ± 3.43 (SD) and +1.82 ± 0.73 with the standard SRK/T and +20.25 ± 3.55 D and +0.13 ± 0.62 D with the double-K SRK/T. No case in the standard SRK/T group and 6 cases (66.66%) in the double-K group achieved a ±0.5 D SE. Conclusion: Double-K modification of the SRK/T formula improved the accuracy of IOL power calculation after LASIK and PRK.