No forward shifting of posterior corneal surface in eyes undergoing LASIK

Purpose: To evaluate structural changes in the cornea and anterior chamber (AC) after LASIK for myopia. Design: Retrospective nonrandomized study. Participants: One hundred sixty-one eyes of 83 patients (mean age, 34.5 +/- 8.3 years) who underwent uneventful LASIK for myopia and myopic astigmatism. The preoperative refractive error (spherical equivalent) and corneal thickness were -6.02 +/- 2.10 diopters (D) and 549.9 +/- 29.3 mu m, respectively. Methods: The AC volume (ACV), AC depth (ACD), corneal thickness, central corneal true net power, and posterior corneal tangential curvature were measured using a rotating Scheimpflug camera before and 1 week and 1 month after surgery. In 84 eyes of 42 cases, anterior and posterior corneal elevations and corneal thicknesses also were measured by scanning-slit topography before and 1 month after surgery. Main Outcome Measures: Time course of the ACV, ACD (central, midperiphery, periphery), corneal thickness, central corneal true net power, posterior corneal tangential curvature using the Scheimpflug camera, and amount of forward shifting of the posterior corneal surface at the center of the difference map using scanning-slit topography. Results: Preoperative and 1-month postoperative mean ACVs were 198.1 mm(3) and 196.4 mm(3), respectively, and preoperative and postoperative mean ACDs (center, midperiphery, periphery) were 3.24, 2.65, and 1.89 mm, and 3.21, 2.63, and 1.87 mm, respectively. The corneal thickness within the optical zone, subjective refraction, and central corneal true net power significantly changed by tissue subtraction after LASIK (P<0.0001). There were no significant differences in the ACV, ACDs (center, midperiphery, periphery), peripheral corneal thickness, and posterior corneal tangential curvature from preoperatively to 1 month after LASIK. However, using scanning-slit topography, the posterior corneal surface displayed a mean forward shift of 29.0 +/- 19.0 mu m 1 month after surgery. Conclusion: The posterior corneal curvature, peripheral corneal thickness, ACDs, and ACV were consistent. These observations indicated that neither forward shifting of the central posterior corneal surface (bulging) nor backward shifting of the peripheral posterior corneal surface due to corneal swelling after ablation occurred after LASIK.