Posterior corneal topographic changes after retreatment LASIK

To evaluate posterior corneal topographic changes after retreatment after myopic laser in situ keratomileusis (repeat LASIK). Retrospective nonrandomized comparative self-controlled trial. Thirty-three eyes of 23 patients who underwent repeat LASIK for residual myopia. Retreatments were performed. Slit-scanning corneal topography was performed before and at 1, 3, and 6 months after repeat LASIK. Posterior corneal topographic changes before and after repeat LASIK were correlated with central corneal pachymetry (preoperatively, before repeat LASIK, after repeat LASIK), residual bed thickness (RBT) and ablation depth (after primary laser in situ keratomileusis (LASIK) and repeat LASIK). On the basis of the amount of posterior corneal elevation after repeat LASIK, the eyes were divided into two groups: group 1 (>66 μm) and group 2 (≤66 μm). Student’s t test/Mann–Whitney rank-sum test was used to determine the significant difference of mean level of each variable between the two groups. After primary LASIK, an increase in posterior corneal elevation had significant positive correlation with attempted correction ( P = 0.02), ablation depth ( P = 0.008), and significant negative correlation with preoperative central pachymetry ( P = 0.0003), RBT ( P = 0.0003), and postoperative central pachymetry ( P = 0.00008). After repeat LASIK, the mean increase in posterior corneal elevation had significant negative correlation with preoperative central pachymetry ( P = 0.03). However, its correlation with the ablation depth ( P = 0.43) during repeat LASIK and RBT after repeat LASIK ( P = 0.11) was statistically insignificant. On multiple linear regression analysis, the attempted correction ( P < 0.01) and RBT after primary LASIK ( P < 0.001) were two independent significant determinants of an increase in posterior corneal elevation after primary LASIK. However, for increase in posterior corneal elevation after repeat LASIK, preoperative central pachymetry ( P < 0.01) and posterior corneal elevation increase after primary LASIK ( P < 0.05) were the two significant determinants. Compared with group 2, group 1 had significantly high values of posterior corneal elevation both after primary LASIK ( P = 0.0037) and after repeat LASIK ( P = 0.0000). This group also had significantly low values of central pachymetry preoperatively ( P = 0.0003) and after primary LASIK ( P = 0.0001) and repeat LASIK ( P = 0.0001) surgeries. The mean RBT after primary LASIK ( P = 0.0006) and after re