In this study, data on corneal posterior elevation were obtained from the Pentacam software. The reference BFS was determined by the central 8.0-mm zone of the preoperative cornea (i.e., the BFS for both preoperative and postoperative maps were identical and were determined from the preoperative data), so that it was the same across all examinations. The corneal posterior elevation and changes were obtained at the center, paracenter (4 points, 1 mm from the center, at 45°, 135°, 225°, and 315° semimeridians), midperiphery (8 points, 2 mm from the center at 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° semimeridians), and peripheral regions (14 points 3 mm from the center at 15°, 45°, 60°, 90°, 120°, 135°, 165°, 195°, 225°, 245°, 270°, 295°, 315°, and 345° semimeridians). In all mathematical analyses, we set 0° at a point on the right and moved counterclockwise in both eyes. All these points were divided symmetrically into superior and inferior hemispheres by the 0° to 180° meridian, with the exception of the center values. Changes in the posterior surface were determined by subtracting the preoperative elevation data from the postoperative elevation data (difference map). The difference in elevation was determined to be the displacement of the posterior corneal surface. An ectatic change (forward protrusion of the posterior corneal surface) would result in a positive number.