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E. Albe, S. Miglior, M. Guareschi, G. Mandelli, S. Gomarasca, N. Orzalesi; Intra- and Inter-observer Reproducibility in the Measurement of Central Corneal Thickness . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4372.
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Purpose: To assess intra- and inter-observer reproducibility of central corneal thickness (CCT) measurement. Methods: 51 volunteers (31 normals, 18 OHT and 2 POAG) underwent three sessions of CCT measurement performed on the same day by three independent observers, for a total of nine measurements. Each session consisted of three repeated CCT measurements separated by a short time interval. The time span between each session was few minutes and the sequence of the three observers was randomly chosen. Each session was performed after a single instillation of topical anesthetic. The Altair (Optikon, Italy) ultrasonic pachimeter was used in the study. The result of each measurement, performed by maintaining the probe perpendicular to the central corneal surface, is expressed as the mean of nine single measurements with the standard deviation (sd). For study purposes, only measurements whose sd was <= 10 micra were considered valid for the analysis. Intra- and inter-observer reproducibility was calculated by means of Intra-class correlation coefficient (ICC). The expected range of variability between two independent evaluations experiment was calculated by the scatter-plots of each test-retest difference vs their mean. The sd of the mean test-retest score differences was used to describe the spread of score differences Results: The ICC ranged between 0.95 and 0.97 for intra-observer evaluation, and between 0.89 and 0.95 for inter-observer evaluation. The expected variability was low (95% confidence interval, <= ± 1% for intra-observer and <= ± 2% for inter-observer evaluation). Conclusions: Measurement of CCT by means of ultrasonic pachimetry is highly repeatable and reproducible. In absolute terms, using the conversion factor suggested by Ehlers et al (1975), the variability induced by CCT evaluation (< ± 1 mmHg) is definitely smaller than the variability observed in IOP measurement (± 2 mmHg) by Goldmann tonometry (Sudesh et al, 1993).
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