Variability of Central Corneal Thickness Measurements—Comparing Zeiss IOL Master and Tomey Corneal Specular Microscope

PURPOSE: The aim of this study was to compare the intraobserver repeatability and agreement of central corneal thickness (CCT) measurements by 2 commonly available instruments, Zeiss IOL Master 700 (SS-OCT-based optical biometry device) and Tomey corneal specular microscope EM-3000 (Noncontact specular microscopy). DESIGN: Retrospective study. METHODS: This is a retrospective analysis of data from routine clinical practice in which preoperative CCT measurements of 105 patients scheduled for cataract surgery were analyzed. Two consecutive CCT measurements were measured using Zeiss IOL Master 700 and Tomey corneal specular microscope EM-3000 by the same examiner. The repeatability of CCT measurements was analyzed by mean intraobserver difference, coefficient of repeatability (CR), and intraclass correlation. The agreement between the 2 methods was analyzed by mean difference and limits of agreement (LoA) using the Bland-Altman method. RESULTS: The mean absolute intraobserver difference between the 2 measurements by Zeiss and Tomey were 3.41 ± 3.98 μm and 8.62 ± 9.52 μm (P < 0.0001), respectively. For Zeiss, the CR was 10.3 μm with 95% LoA of −10.5 to 10.1 μm. For Tomey, the CR was 25.2 μm with 95% LoA of −25.2 to 25.2 μm. The mean CCT measurements ± standard deviation by Zeiss and Tomey were 544.0 ± 38.1 μm and 532.6 ± 40.0 μm, respectively (P = 0.003). The 95% LoA in CCT between the 2 methods was −15.8 to 38.7 μm. CONCLUSIONS: Zeiss IOL Master 700 has superior intraobserver repeatability and consistency than Tomey EM-3000. Zeiss produced higher CCT measurements than Tomey; hence, in clinical practice, interchangeability between these 2 methods is limited.