Correlational study of central corneal thickness measurements on Hong Kong Chinese using optical coherence tomography, Orbscan and ultrasound pachymetry

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Abstract
Background Central corneal thickness (CCT) of 74 eyes from 39 normal Hong Kong Chinese subjects with ages ranging from 39 to 86 years were studied. Aim & Purpose To compare the measurements of different devices and to compare the results of ethnic groups in other studies. Methods Non-contact measurements by Orbscan and Optical Coherence Tomography (OCT) were first carried out, followed by contact measurement using Ultrasound Pachymetry. The results of five measurements of Ultrasound Pachymetry and three measurements of OCT and Orbscan were each averaged and compared using correlation, linear regression and one-way analysis of variance methods. Results The measurements of three devices were significantly correlated (P < 0.01). The mean CCT in our study group measured by Orbscan (with an acoustic factor set at 0.92), Ultrasound Pachymetry and OCT were 555.96 ± 32.41, 555.11 ± 35.30 and 523.2 ± 33.54 μm respectively. A linear regression model (using ultrasound measurements as standard) was presented. Conclusions When a correction factor of 32 μm was applied to OCT measurements, the means of three devices became significantly equal. The adjusted OCT measurements were less precise within subjects but more accurate than Orbscan when compared with ultrasound pachymetry as a reference standard. The mean CCT measurement of our sample was comparable to some studies on Hong Kong Chinese, Caucasians and Japanese but higher than those on some Europeans, Asian and North Americans of African origin.