Comparison of Posterior Corneal Imaging Before and After LASIK Using Dual Rotating Scheimpflug and Scanning Slit-Beam Corneal Tomography Systems

Abstract

To compare the maximum posterior elevation (MPE) measurements before and after LASIK using a dual rotating Scheimpflug (DRS) imaging system (Galilei, Ziemer Ophthalmic Systems, Port, Switzerland) and a scanning slit-beam (SSB) imaging system (Orbscan IIz, Bausch & Lomb, Rochester, NY). This retrospective study included 78 eyes from 78 patients who underwent myopic LASIK. Preoperative and postoperative data collected included anterior and posterior best-fit sphere radius and axial curvature readings, posterior central elevation (PCE), and MPE relative to a best-fit sphere using a 7.8-mm region of interest. Data were compared using paired t test analysis. Mean preoperative PCE (5.06 ± 2.29 μm with the DRS system and 12.78 ± 6.90 μm with the SSB system) and MPE (4.87 ± 4 μm with the DRS system and 15.44 ± 9.78 μm with the SSB system) were statistically different (P < .001). Mean postoperative PCE (4.55 ± 2.34 μm with the DRS system and 20.59 ± 8.11 μm with the SSB system) and MPE (4.90 ± 3.35 μm with the DRS system and 24.95 ± 10.15 μm with the SSB system) were statistically different (P < .001). The difference between preoperative and postoperative MPE measurements by DRS was not statistically significant (P = .953), whereas the difference measured by SSB was statistically significant (P < .001). The consistency of DRS measurements suggests that the posterior surface of the cornea does not change appreciably after keratorefractive surgery and is imaged more accurately using DRS compared with SSB. The DRS system affords confidence in interpreting data that are useful for discerning morphologic abnormalities of the cornea, both before and after keratorefractive surgery.