Correlation between factors related with previous myopic laser in situ keratomileusis and refractive error after intraocular lens implantation

Abstract

Purpose: In eyes after myopic laser in situ keratomileusis (LASIK), power of intraocular lens (IOL) is underestimated by using conventional methods of IOL power calculation. Although plenty of calculation methods have been proposed, regression analysis of IOL power underestimation with respect to LASIK correction was rarely performed. This retrospective study was to evaluate factors related with refractive error after IOL implantation in post- myopic LASIK eyes.

Methods: Clinical records of eyes that had previously undergone myopic LASIK and received IOL in cataract surgery were observed. The study comprised of 30 eyes of 20 patients whose mean age was 58.8 years at cataract surgery. Period between LASIK and cataract surgeries was 2 to 13 years (mean: 9.6 years). All target refractions in LASIK were intended to emmetropia. Manifest refractions spherical equivalent (MRSEs) and keratometric refractions (Ks) were recorded before LASIK, and before and 1 month after cataract surgery. Ocular axial length (AXL) was also measured before cataract surgery. Predicted postoperative refraction was obtained by SRK/T and double-K formulas, and the difference from MRSE at 1 month was calculated as refractive error. Correlations between refractive error and, MRSE before LASIK, change in K between before LASIK and cataract surgeries, and AXL were analyzed with linear and multiple regression analyses.

Results: MRSE before LASIK was -2 to -13 D (mean: -7.5 D), and change in K was -1.06 to -8.00 D (mean: -4.37 D). Refractive error was 0.03 to 4.99 D (mean: 1.98 D) in the SRK/T, that was significantly correlated with MRSE before LASIK, change in K, and AXL (P < 0.0001, R² = 0.51, 0.56, 0.52, respectively). Multiple regression analysis showed that refractive error had significant associations with change in K and AXL (P = 0.004 and 0.005, slope = -0.54 and 0.46 D/mm, respectively). In the double-K, significant correlation was found between refractive error and AXL (P = 0.001, slope = 0.38 D/mm).

Conclusions: In post-myopic LASIK eyes, refractive error was highly correlated with the amount of myopic correction in SRK/T formula. Significant correlation with AXL were found in both SRK/T and double-K formulas. This result demonstrated that compensation of K values only is not sufficient for IOL power calculation of post-LASIK eyes.