The shape of posterior corneal surface in normal, post-LASIK, and post-epi-LASIK eyes

PURPOSE. To evaluate the shape of the posterior corneal surface in eyes with normal myopia or myopic astigmatism and the changes after LASIK and epi-LASIK. METHODS. A total of 152 eyes were included in the study. The posterior corneal elevation was measured with Scheimpflug imaging (Pentacam; Oculus, Wetzlar, Germany), before LASIK or epi-LASIK and at 1 and 6 months after surgery, along the four optical zones (center and 2-, 4-, and 6-mm diameters) as a function of the meridian. RESULTS. In normal eyes, the heights were lower in the vertical meridian than in the horizontal meridian and were also lower in the superior hemisphere than in the inferior hemisphere. In post-LASIK eyes, almost all regions protruded 1 month after surgery, except for the 6-mm diameter, which exhibited a slight but not significant (P = 0.731) backward displacement. The various elevations returned to original levels 6 months after LASIK. In the post-epi-LASIK group, there was a significant backward displacement in the center and 2-mm regions after surgery. Moreover, there was no shift at the 4-mm diameter, and the 6-mm diameter showed a progressive forward shift. CONCLUSIONS. The shape of the normal posterior corneal surface exhibited obvious regional disparities and radial asymmetry. The displacement after LASIK was observed as time-dependent changes that protruded at an early stage but then returned to original levels 6 months after surgery. On the other hand, the displacement after epi-LASIK appeared as region-dependent changes that could be divided into central and peripheral parts that displayed backward and forward shift trends, respectively.