Comparison of central corneal thickness measurements using three different instruments

Objective To compare the difference in central corneal thickness(CCT) measurements using a Pentacam,an Orb-scan-Ⅱ topography system and A-scan ultrasound pachymetry.Methods The CCTs of 252 healthy eyes(from 126 myopic subjects) were measured with a Pentacam,Orbscan-Ⅱ and A-scan ultrasound pachymetry.The differences between the instruments were evaluated with paired t-tests.The correlation between the measurements was evaluated using Pearson correlation coefficients.Results Of the 252 eyes,the CCT values obtained with the Pentacam,Orbscan-Ⅱ and A-scan ultrasound pachymetry were(546.3±33.6) μm,(550.5±38.5)μm and(538.6±35.4)μm,respectively.There was a high correlation among them.The CCT values obtained with A-scan ultrasound pachymetry were the lowest among the three mea-surements.This sample(252 eyes) was divided into 3 groups according to the CCT measurements obtained with A-scan ultrasound pachymetry.In group 1,71 eyes had CCT values less than 520 μm.The CCT values with A-scan ultrasound pachymetry were thin-ner than those obtained with a Pentacam or A-scan ultrasound pachymetry.The differences were significant(P =0.000,P =0.001).There were no statistically significant differences between Orbscan-Ⅱ and Pentacam measurements.In group 2,154 eyes had CCT values from 520 μm to 580 μm.The CCT values obtained with an Orbscan-Ⅱ were thicker than those obtained with a Pentacam and the CCT values with a Pentacam were thicker than those ob-tained with an A-scan ultrasound pachymetry.The differences were significant(P=0.000,P=0.000).In group 3,27 eyes had CCT values of more than 580 μm.The CCT values with Orbscan-Ⅱ were thicker than those obtained with a Pentacam or A-scan ultrasound pachymetry.The differences were significant(P=0.000,P=0.000).There were no statistically significant differences between A-scan ultrasound pachymetry and Pentacam.Conclusion Pentacam,Orbscan-Ⅱ and A-scan ultrasound pachymetry cannot be used interchangeably when measuring central corneal thickness.