Central corneal thickness measurements with partial coherence interferometry, ultrasound, and the Orbscan system☆
Received 8 January 2003; accepted 5 September 2003.
Abstract
Objective
To compare the reliability of central corneal thickness measurements (CCT) obtained with partial coherence interferometry (PCI), ultrasound pachymetry, and the Orbscan system.
Design
Cross-sectional study.
Participants
Twenty healthy subjects with CCT measurements in both eyes.
Methods
The CCT measurements were obtained with PCI, ultrasound pachymetry, and the Orbscan system. In each eye, 2 investigators performed 5 repeated measurements with each pachymetric device. Intraclass correlation coefficients (κ) were calculated and mean CCT measurements were compared.
Main outcome measures
The CCT measurements obtained with ultrasound pachymetry, the Orbscan system (Orbtek Inc., Salt Lake City, UT), and PCI.
Results
Mean CCT values measured with ultrasound pachymetry were significantly thicker than those measured with PCI (21.5 μm; P<0.001) or the Orbscan system (19.8 μm; P<0.001). The correlation coefficients for the intraobserver variability were 0.999 for PCI measurements, 0.983 for ultrasound pachymetry measurements, and 0.988 for Orbscan system measurements. The correlation coefficients for the interobserver variability were 0.998 for PCI measurements, 0.980 for ultrasound pachymetry measurements, and 0.988 for Orbscan system measurements. There was a slightly better consistency between ultrasound pachymetry and PCI (κ = 0.96) than between the Orbscan system and PCI (κ = 0.92) and between ultrasound pachymetry and the Orbscan system (κ = 0.89).
Conclusions
Partial coherence interferometry was the method with the least intraobserver or interobserver variability. Mean CCT as measured with ultrasound pachymetry was approximately 20 μm thicker than with the Orbscan system and PCI. However, corneal thickness measurements with ultrasound pachymetry and PCI were slightly more consistent than those of the Orbscan system and PCI. This slightly better consistency, however, may be important, especially in corneal refractive surgery.
1Department of Ophthalmology, University of Vienna, Vienna, Austria
2Institute of Medical Physics, University of Vienna, Vienna, Austria
3Department of Clinical Pharmacology, University of Vienna, Vienna, Austria
Correspondence to Georg Rainer, MD, Department of Ophthalmology, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria.
ABSTRACT