The comparison of reliability and repeatability of four different non contact devices in regardi̇ng of central corneal thickness measurement

Purpose: The aim of this study is to compare central corneal thickness measurement values within four different devices that make non-contact measurement. Materials and Methods: In this study, 130 healthy individuals without ophthalmologic pathology except refractive error, who applied to Manisa Celal Bayar University Faculty of Medicine, Department of Ophthalmology, have been included. Detailed ophthalmologic examination has been performed for all cases. Data have been recorded by performing three repeated measurements with devices which are Scheimpflug camera (Pentacam, Oculus Optik gerate GmbH, Wetzlar, Germany), Specular microscope Cellchek XL (Konan Medical USA, Torrance, CA, USA), Lenstar LS 900®, (Haag-Streit AG, Switzerland) and ÖS-OKT Cirrus (Carl Zeiss Meditec, Inc. Dublin, CA). All measurements have been analyzed by intragroup correlation (ICC), Anova-Friedman test and Bland-Almant plot. Results: The average age of patients included in this study is 27,81 ± 8,28 (min: 20; max: 71). 44 of the people are male (33,8%), 86 of them are female (66,2%). Mean CCT measurement values are 553,61 ± 42,71 μm with SM, 546,42 ± 34,77 μm with Pentacam, 543,48 ± 35,45 μm with Lenstar, and 538,96 ± 35,97 μm with OS-OCT. There has been no statistically significant difference between three repeated measurements within these four devices (respectively; p: 0,449, p: 0,270, p: 0,540, p: 0,881). ICC values were 0,972, 0,997, 0,998 and 0,998, respectively. The mean difference between OS-OCT and Lenstar measurements is 14,66 μm and the 95% confidence interval limits are 10,14 μm to -19.18 μm. The mean difference between OS-OCT and SM measurements is 31,86 μm and the 95% confidence interval limits are 46,50 μm and -17,22 μm. The mean difference between OS-OCT and Pentacam measurements is 12,87 μm and the 95% confidence interval limits are 20,33 μm to -5,41 μm. The mean difference between Pentacam and Lenstar measurements is 17,28 μm and the 95% confidence interval limits are 20,22 μm to -14,34 μm. The mean difference between Pentacam and SM measurements is 30,22 μm and the 95% confidence interval limits are 37,40 μm and -23,04 μm. The mean difference between SM and Lenstar measurements is 31,92 μm and the 95% confidence interval limits are 42,04 μm to -21,80 μm. Conclusion: The CCT measurement values of four different devices are very compatible and reproducible. The highest CCT values have been obtained with the SM device and the lowest CCT values have been obtained with the OS-OKT device. The least difference in mean CCT measurement values has been observed between OS-OCT and Pentacam devices. Measurements with Pentacam and Lenstar are also close to each other. The greatest difference in average CCT measurement values is between SM and Lenstar devices. In clinical practice, CCT measurements obtained with SM and values measured with the other three devices should not be used interchangeably. Keywords: Central corneal thickness, pachymeter, repeatability, Bland-Altman plot