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From the UCLA Laser Refractive Center (MES, JD, DRH), Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, California; the Cornea and Refractive Surgery Division (AR-M), Instituto de Oftalmologia, Mexico City, Mexico; the Cornea Division and Eye Research Center (SZ-G), Mashad University of Medical Sciences, Mashad, Iran; and the Cornea and External Disease Division (JE), Department of Ophthalmology, University of Colorado School of Medicine, Aurora, Colorado.
Dr. Hamilton has received honoraria for educational lectures from Ziemer Ophthalmic Systems. The remaining authors have no financial or proprietary interest in the materials presented herein.
Accurate imaging of the anterior and posterior cornea is essential for the refractive surgeon to screen patients effectively for surgery.1 Tomography systems currently available in the United States include the Orbscan IIz (Bausch & Lomb, Rochester, NY) (scanning slit-beam [SSB] technology, and Placido imaging); Pentacam (Oculus Optikgeraete GmbH, Wetzlar, Germany) (single rotating Scheimpflug [SRS] system); Galilei (Ziemer Ophthalmic Systems, Port, Switzerland) (dual rotating Scheimpflug [DRS] system and Placido imaging); and Visante Omni (Carl Zeiss Meditec, Dublin, CA) (anterior segment optical coherence tomography and Placido imaging). Abnormal posterior corneal elevation has been shown to aid in the identification of forme fruste keratoconus and early detection of postrefractive keratectasia.2,3 However, most of the studies that evaluated posterior corneal elevation changes after refractive surgery were based on SSB measurements.4-10 The SSB system uses both slit scanning and a Placido system to measure anterior and posterior elevation as well as anterior curvature.11 Several studies conducted with SSB technology suggested that the posterior corneal surface moves forward after LASIK,4,6,9 although these findings may be artifactual.12 Studies using the Pentacam, an SRS system, showed no difference in posterior corneal elevation after refractive surgery.13-16 The DRS system may provide more accurate corneal measurements in eyes after refractive surgery.17 This study compared maximum posterior elevation (MPE) measurements obtained preoperatively and after myopic LASIK surgery with SSB and DRS technologies.
Patients and Methods
Patient Selection
A retrospective chart review was performed after institutional review board approval was obtained at the University of California, Los Angeles (UCLA), on patients who underwent LASIK surgery at the UCLA Laser Refractive Center, Jules Stein Eye Institute, David Geffen School of Medicine at UCLA. Seventy-eight eyes of 78 patients who underwent myopic...