Comparison of central corneal thickness measurements by specular microscopy, ultrasound pachymetry, and ultrasound biomicroscopy

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Abstract
To compare the reproducibility and mean values of central corneal thickness (CCT) obtained by specular microscopy, ultrasound pachymetry, and ultrasound biomicroscopy (UBM). Department of Ophthalmology, University of Toronto, Toronto, Ontario, Canada. Thirty-one healthy volunteers were recruited for a sample size of 62 eyes. All subjects had pachymetric measurements by specular microscopy, ultrasound pachymetry, and UBM. Three separate measurements meeting criteria for centrality and perpendicularity were recorded for each eye. The mean CCT by specular microscopy was 572 μm (95% confidence interval (CI), 566-578 μm), which was significantly greater than 550 μm (95% CI, 545-556 μm) (P<.001) and 555 μm (95% CI, 550-560 μm) (P<.001) by ultrasound pachymetry and UBM, respectively. The mean standard deviation (SD) of repeated measurements by specular microscopy was 7.82 μm, which was significantly greater than the mean SDs of 4.14 μm (P<.001) and 3.90 μm (P<.001) by ultrasound pachymetry and UBM, respectively. There was no statistically significant difference between the mean SDs by ultrasound pachymetry and UBM (P=.156). Although the CCT measurements by specular microscopy were significantly less reproducible than those by ultrasound pachymetry and UBM, the error levels were clinically acceptable. Both ultrasound pachymetry and UBM produced similar CCT measurements, which were significantly less than those generated by specular microscopy. One should be aware of the advantages and limitations of each machine and of possible differences in the CCT measurements by optical and ultrasound pachymetry.