Background and Objective. Evaluation of agreement, repeatability, and reproducibility of central and minimal corneal thickness (CCT and MCT) measurements obtained by SOCT, the Scheimpflug system, and ultrasound pachymetry. Materials and Methods. 28 eyes of healthy patients were enrolled. Pachymetry measurements were performed with SOCT, the Scheimpflug system, and ultrasound instrument. Each measurement was taken by 3 operators on 3 devices providing a total of 2100 measurements. Results. The mean CCT for SOCT, Scheimpflug system, and ultrasound instrument was 537.92, 545.94, and 555.74？μm, respectively, ( ). The respective mean coefficients of repeatability for CCT were 0.61, 0.82 and 0.80, whereas mean coefficients of interoperator reproducibility for CCT were 0.91, 1.11, and 1.25. Conclusions. CCT and MCT measurements show moderate agreement between instruments. The repeatability and interoperator reproducibility of the results obtained by SOCT are somewhat higher. The operator's impact on CCT and MCT measurements is insignificant in all devices. 1. Introduction Central corneal thickness (CCT) measurement plays a major role in diagnostic and therapeutic approaches to corneal pathology and has an important impact on intraocular pressure readings. An ideal method of corneal thickness measurement should be accurate, repeatable, reproducible, and safe, as well as easy and quick to perform. CCT can be assessed by means of many instruments, including specular microscopy, confocal microscopy, ultrasound pachymetry, ultrasound biomicroscopy (UBM), slit-scanning corneal topography, the Scheimpflug system, optical biometry, and spectral optical coherence tomography (SOCT). Ultrasound pachymetry, which used to be a gold standard for measuring corneal thickness, is a contact method where the place of measurement is strongly dependent on the operator [1]. Therefore, other noninvasive methods have gained popularity; nevertheless, the accuracy of some of these methods has not been thoroughly examined. The most important features of a measuring technique are accuracy and precision. Because the true value of the corneal thickness of a particular eye is unknown, it is impossible to calculate the accuracy of measurements. Therefore, the agreement between new devices and an instrument considered to be a gold standard should be used. The precision of measurements may be stratified into repeatability and reproducibility. Repeatability is defined as the variability of results obtained from one object in the same measurement conditions (time, instrument, technique, place,
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