Clinical Study of Forward Shift of Posterior Corneal Surface after LASIK and LASEK in High Myopia

Objective To compare the forward shift of posterior corneal surface after laser in situ keratomileusis (LASIK) and laser subepithelial keratomileusis (LASEK) in high myopia. Methods 31 eyes of 17 patients with LASIK and 28 eyes of 15 patients with LASEK were included in this study, whose spherical equivalent were more than -6.0 diopters (D). Corneal topography was obtained with Orbscan Ⅱ preoperatively and 1day, 2 week, 1 month, 3 months and 6 months postoperatively. The amount of forward shift of the posterior corneal surface were assessed using the difference map of an Orbscan Ⅱ, which was generated from the preop-erative and subsequent postoperative elevation map. Results The posterior corneal surface had shifted for-ward significantly after LASIK or LASEK (P0.05). In LASIK group the forward shift of the posterior corneal surface at 1, 3 and 6 months were less than that at 1 day and 2 weeks postoperatively. Furthermore, the forward shift of the posterior corneal surface in LASIK group was more than that in LASEK group at 2 weeks postopera-tively (P0.05). Conclusions Refractive surgery induced a forward shift of the posterior corneal surface after LASIK or LASEK in high myopia, and this change after LASIK was more than that after LASEK early postoperatively.