Assessment of central corneal thickness and corneal endothelial morphology using ultrasound pachymetry, non-contact specular microscopy, and Confoscan 4 confocal microscopy

Background: The aim was to compare the repeatability, reproducibility and inherent precision of ultrasound pachymetry (USP), noncontact specular microscopy (SP-2000P) and the Confoscan 4 confocal microscope (z-ring CS4) in measuring endothelial cell density (ECD), coefficient of variation of cell size (CV), and central corneal thickness (CCT) in normal eyes. Methods: In this prospective study, one eye was selected from each of 30 subjects for the measurements of ECD, CV and CCT, which were taken by two observers. Results were analyzed statistically by repeated-measures analysis of variance (ANOVA) for intra-observer repeatability, inter-observer reproducibility, unpaired t-test, paired t-test, and Bland-Altman analyses to determine limits of agreement (LOA) between the three instruments. Results: Mean ECD, measured by SP-2000P and z-ring CS4, were 3115.50 +/- 279.70 cells/mm(2) and 3167.50 +/- 264.75 cells/mm(2), respectively (observer 1), and 3192.63 +/- 249.42 cells/mm(2) (z-ring, observer 2). Mean CV measurements were 27.12 +/- 2.51 and 27.10 +/- 2.41 (SP-2000P and z-ring CS4, respectively; observer 1), and 27.17 +/- 2.25 (z-ring, observer 2). Mean CCT values were 555.11 +/- 35.83 mu m (USP), 535.82 +/- 41.10 mu m (SP-2000P) and 552.57 +/- 36.83 mu m (z-ring CS4), and 554.97 +/- 36.34 mu m (z-ring CS4, observer 2). However, pairwise tests in all cases there was good repeatability and reproducibility as shown by inter-observer and intra-observer analysis of variance for each of the instruments. Conclusions: The SP-2000P and the z-ring CS4 can be used interchangeably to measure ECD and CV. For CCT, the sample size was too small to test for differences of the CCT measurements between the three instruments.