Correlation between estimated and measured corneal ablation and refractive outcomes in laser in situ keratomileusis for myopia

Purpose: To evaluate the difference between the measured and the intended postoperative central corneal thickness (CCT) by optical low-coherence reflectometry (OLCR) for 3 months after myopic laser in situ keratomileusis (LASIK) and correlate it with refractive outcomes. Setting: Center for Refractive Therapy, Department of Ophthalmology, Ludwig-Maximilians-University Munich, Germany. Methods: The CCT was measured by OLCR before and 6 weeks and 3 months after myopic LASIK. The correlation between the difference in pachymetry and the difference in the measured and planned postoperative refraction was proven by linear regression and Pearson product moment correlation analysis (P<.05). In a subset of eyes with a 7.0 mm optical zone, the effect of the calculated ablation depth on the difference in pachymetry was evaluated. Based on the laser algorithm data, the intended ablation was 100 μm or less in Subgroup 1 and 100 μm or more in Subgroup 2. Results: Forty-three eyes of 25 patients were evaluated, with 25 eyes in the subset. The difference between the measured and intended postoperative CCT was 11.1 μm ± 8.1 (SD) at 6 weeks and 13.8 ± 7.5 μm at 3 months. The correlation between this difference and the difference in refraction was poor (r² = 0.005 μm and r² = 0.009, respectively). With greater ablation depth (Subgroup 2), the difference in pachymetry decreased by 3 months postoperatively. Conclusion: The lack of correlation between differences in the measured and intended CCT and the final refraction shows the complexity of intraoperative variables in LASIK and the effect of individual wound healing.