Correlation Between Measured and Predicted Keratometry after Myopic Astigmatic LASIK

Abstract

Abstract: : Purpose: To compare the post-LASIK corneal curvature predicted by the Nidek EC-5000 excimer laser to the post-LASIK corneal curvature measured by computed corneal topography. Methods: A retrospective chart review of 100 patients with myopic astigmatism who underwent LASIK by one surgeon (F.T.) using the Nidek EC-5000 excimer laser was performed. The postoperative corneal curvature predicted by the laser program was compared to the postoperative corneal curvature measured by computed corneal topography. Inclusion criteria were myopic astigmatism and pre- and post-surgical topography recorded by the same instrument. Patients who had surgical enhancement, monovision correction, or co-management with postoperative topography performed at other facilities were excluded. Results: Twenty-seven eyes from fourteen patients met criteria for study inclusion. Mean manifest preoperative spherical equivalent was -2.694 +/- 1.12. Mean predicted postoperative corneal curvature was 42.293 +/- 1.914 diopters. Mean measured postoperative corneal curvature was 41.708 +/- 1.915 D. The mean difference (0.584) was statistically significant (P<.0215). There was a statistically significant overestimation of final corneal curvature by the Nidek laser program in patients with astigmatism > 1 cylinder(P< .0002) and in patients with preoperative corneal curvature > 44 D (P< .0004). Conclusions: The Nidek EC-5000 laser program overestimates the postoperative corneal curvature when LASIK is performed on patients with astigmatism > 1 cylinder or preoperative corneal curvature > 44 D. This knowledge may aid the LASIK surgeon in predicting postoperative outcome. Further study with increased sample size, comparison with other surgeons, lasers, and further sub-group analysis may elucidate significant factors in final corneal power prediction.

Keywords: refractive surgery: LASIK