Comparison of ultrasound pachymetry and partial coherence interferometry in the measurement of central corneal thickness

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Abstract
To compare central corneal thickness (CCT) measurements obtained with 3 ultrasound pachymeters and with partial coherence interferometry (PCI) and evaluate the effect of repeated contact by a pachymetry probe on corneal thickness. Department of Ophthalmology, University of Vienna, Vienna, Austria. Central corneal thickness was measured in 20 eyes of 20 healthy volunteers with 3 different ultrasound pachymeters (DGH 500, DGH Technology Inc.; SP 2000, Tomey Inc.; Paxis, Biovision Inc.) and with PCI. In each eye, 5 measurements with PCI were followed by 5 measurements with each ultrasound pachymetry device and another 5 measurements with PCI. The mean CCT measured with the DGH 500, SP 2000, and Paxis was 541.0 μm, 539.2 μm, and 545.1 μm, respectively. Although the differences among the 3 ultrasound pachymetry devices were within 6.0 μm, they were statistically significant (P< .05). The PCI measurements were significantly smaller (P <.05) than the ultrasound measurements: 518.8 μm before and 517.5 μm after repeated contact with the ultrasound pachymetry probe (P <.05). The mean precision (standard deviation) was 0.77 μm for PCI and between 2.40 μm and 3.58 μm for ultrasound pachymetry measurements. The correlation coefficients for the intraobserver variability were 0.999 for PCI and between 0.987 and 0.995 for ultrasound pachymetry measurements. Partial coherence interferometry was the more precise method of measuring CCT and had better intraobserver variability. Repeated contact by a pachymetry probe reduced corneal thickness by 1.3 μm. However, the reason for the smaller measurements with PCI than with ultrasound pachymetry remains unclear.
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