Central Corneal Thickness Measurements with Different Imaging Devices: Ultrasound Pachymetry, Noncontact Specular Microscopy, and Tono-Pachymetry

Objectives: Investigation of the compatibility between central corneal thickness (CCT) measurements in healthy eyes by comparing standard ultrasound pachymetry (USP) with noncontact tono-pachymetry (NCT) and specular microscopy (SM) devices was aimed. Methods: Forty-five eyes of 45 healthy volunteers aged between 18 and 60 years were included in this study. CCT of all cases was evaluated with USP, NCT, and SM devices. The same examiner performed all examinations. Bland–Altman plots and intraclass correlation coefficients were used to evaluate the agreement between instruments. Results: The mean age of the patients was 31±10.2 years. Fifteen (33.3%) cases were male and 30 (66.7%) were female. The mean CCT measured using NCT (559.3±39 µm) was significantly higher than those measured using SM (534.8±41 µm) and USP (542.6±43 µm, p<0.001). Bland–Altman analysis showed that the difference between the first, second, and third measurements was evenly dispersed around the mean, with no clear trend toward over- or underestimation by either NCT, USP, or SM. The 95% limits of agreements were 0.30–48.72 µm for NCT, –12.63–46.04 µm for the USP, and –24.41–8.80 µm for the SM. Correlation analysis between the three devices showed a very strong positive correlation (p<0.001). Conclusion: Significant differences were observed between CCT measurements in healthy individuals used in ophthalmology practice and performed with different devices. This situation should draw attention to the fact that in diseases such as glaucoma and endothelial insufficiency, corneal thickness monitoring should be done with the same device and the devices should not be used interchangeably.