CLINICAL SCIENCE Comparison of Central Corneal Thickness, Thinnest Corneal Thickness, Anterior Chamber Depth, and Simulated Keratometry Using Galilei, Pentacam, and Sirius Devices Mustafa A. Anayol, MD,* Emre Güler, MD,† Ramazan Ya gcı, MD,‡ Mehmet A. S ¸ ekero glu, MD,* Meltem Yılmazo glu, MD,* Hakan Tırhıs ¸, MD,* Ali E. Kulak, MD,† and Pelin Yılmazbas ¸, MD* Purpose: The aim was to evaluate the agreement in the central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), and mean simulated keratometry (simK) measurements using Pentacam, Galilei, and Sirius Scheimpflug systems in normal eyes. Methods: Anterior segment measurements were performed with Pentacam, Galilei, and Sirius devices in 32 healthy subjects. The right eye of each participant was selected. Measurements obtained with the 3 systems were compared using repeated- measures analysis of variance and Bonferroni multiple compar- isons test. Results: Analysis of variance determined a significant difference in the anterior segment measurements of CCT, TCT, ACD, and simK between the 3 devices (P , 0.001). Pairwise comparisons of CCT and TCT measurements were significantly different except for the comparison between Pentacam and Sirius. All pairwise com- parisons for ACD were statistically significant. The pairwise com- parison results for simK values showed that the Galilei and Sirius systems demonstrated better agreement with each other than with Pentacam. Conclusions: The results of this study suggest that the Pentacam, Galilei, and Sirius Scheimpflug systems should not be accepted as interchangeable for CCT, TCT, ACD, and simK in healthy subjects. Key Words: central corneal thickness, thinnest corneal thickness, anterior chamber depth, simulated keratometry, Pentacam, Galilei, Sirius (Cornea 2014;33:582–586) A ccurate measurements of keratometry, corneal thickness, and anterior chamber depth (ACD) are crucial to the design and ultimate success of vision corrective procedures such as refractive and cataract surgery. 1–5 The introduction of Scheimpflug cameras into clinical practice has significantly improved capabilities of imaging the anterior eye segment that were not possible until a few years ago. In 2002, the first rotating Scheimpflug camera, the Pentacam (Oculus Optikg- eräte GmbH, Wetzlar, Germany), 6,7 was introduced. More recently, the Galilei (Ziemer Ophthalmic Systems AG, Zurich, Switzerland) 8 and the Sirius (Costruzione Strumenti Oftalmici, Florence, Italy), 9 combination of Scheimpflug camera with a Placido topography system, were introduced. To acquire keratometric data of the anterior corneal surface, Pentacam uses only the Scheimpflug images, whereas the Galilei and Sirius use the Placido disk. 10–12 These noncontact methods are able to assess many anterior segment parameters including the total corneal dioptric power (ie, the dioptric power of the whole cornea, including the anterior and posterior surfaces), corneal pachy- metry, the ACD, and volume. Although other studies have assessed the agreement of the Pentacam measurements with Galilei separately 12–14 and the agreement of the Pentacam with Sirius, 15,16 it has not been clear whether the results of these devices are comparable and whether they can be used interchangeably. Therefore, we compared the anterior seg- ment parameters measured with Pentacam, Galilei, and Sirius in healthy corneas. MATERIALS AND METHODS This prospective study was managed in accordance with the Helsinki Declaration. All participants were informed about the aim of the study and had given informed consent. All of the subjects included in this study were healthy except for any refractive error. The exclusion criteria were any ocular or systemic disease or contact lens usage within 2 weeks or history of any ocular surgery or history of any ocular trauma. The right eye of each participant was selected. In 2 cases Galilei and in 1 case Pentacam was unable to obtain a scan of acceptable quality after 5 attempts, whereas the sequential measurements obtained by the other devices were acceptable for these cases. Therefore, we included the left eye of these Received for publication January 13, 2014; revision received February 23, 2014; accepted February 25, 2014. Published online ahead of print April 23, 2014. From the *Department of Ophthalmology, Ulucanlar Eye Training and Research Hospital, Ankara, Turkey; †Department of Ophthalmology, Tur- gut Özal University School of Medicine, Ankara, Turkey; and ‡Department of Ophthalmology, Pamukkale University School of Medicine, Denizli, Turkey. The authors have no funding or conflicts of interest to disclose. Reprints: Emre Güler, Department of Ophthalmology, Turgut Özal University School of Medicine, Alparslan Türkes Cad, No. 57, 06510 Emek, Ankara, Turkey (e-mail: guleremre83@hotmail.com). Copyright © 2014 by Lippincott Williams & Wilkins 582 | www.corneajrnl.com Cornea  Volume 33, Number 6, June 2014