Comparison of different corneal residual bed thickness after small incision lenticule extraction (SMILE)

Purpose To evaluate the corneal biological parameters stability between the different corneal residual bed thickness (RBT) after Small Incision Lenticule Extraction (SMILE). Methods In this prospective clinical trial, 127 eyes of 64 patients underwent SMILE. According to the corneal RBT, the patients were divided into the 250-270 & mu;m, 270-290 & mu;m and 290-310 & mu;m groups. Corvis ST (Oculus Optikgerate GmbH, Wetzlar, Germany) and Scheimpflug camera (Pentacam; Oculus Optikgerate GmbH, Wetzlar, Germany) measurements were performed preoperatively, 1 day, 1week, 1month and 3 months after surgery. Results The keratometer values among the three groups were no significant differences in postoperative periods (each P > 0.05), except the corneal thickness values (each P < 0.05). In the 250-270 & mu;m and 270-290 & mu;m groups, the keratometer and corneal thickness values were decreased at postoperative 1 week and increased at 1 and 3 months. The 290-310 & mu;m group significantly higher posterior maximum elevation (PME) than the 250-270 & mu;m group at 1 and 3 months (P = 0.022, 0.022, respectively), and higher preoperative thinnest point (PTE) at 1 week and 1 month (P = 0.013, 0.035, respectively). The PME of the 290-310 & mu;m group was higher than the 270-290 & mu;m group at 3 months (P = 0.045), and higher PTE at 1 week and 3 months (P = 0.022, 0.02, respectively). In all three groups, the maximal deformation amplitude (DA) was significantly higher at 1 and 3 months compared to postoperative 1 day and 1 week, and the IOP was decreased at 1 month then recovered at 3 months (each P < 0.05).The DA of the 250-270 & mu;m group was significantly higher than the 290-310 & mu;m group at postoperative 1 week, 1 and 3 months (P = 0.001, 0.01, 0.02, respectively). The change of the posterior corneal elevation and biomechanical parameters values were no significant differences among the three groups in postoperative periods (each P > 0.05). Conclusions The range of 250-310 & mu;m RBT was safe and stable at the early postoperative of SMILE. The RBT may be positively correlated with the posterior corneal elevation.