Comparison of central corneal thickness measured with Orbscan-II , Pentacam and ultrasonic pachymetry

Objective To assess the reliability of Orbscan-II , Pentacam and ultrasonic pachymetry （US） for central corneal thickness （CCT） measurements. Methods Central corneal thickness was measured using Orbscan-II , Pentacam and ultrasonic pachymetry in 159 preoperative cases （318 eyes）. Patients were further divided into three groups according to corneal thickness （〈500 um group, 500-570 um group and ≥570 um group） as determined by ultrasonic pachymetry and the differences in the measurements obtained by all three methods were statistically analyzed for the three groups. Results The mean CCT readings with Orbscan-II , Pentacam, and ultrasonic pachymetry were （527.9＋-43.0）um, （526.3＋-38.4）um, and （522.6＋-37.8）um, respectively. No statistically significance differences were found among the three instruments （F=1.491, P=0.226） using analysis of variance. After the patients were divided into three groups based on the ultrasonic pachymetry measurements, the results showed that there was no statistically significant difference in measurements by the three instruments for the 〈500 um group and the 500-570 um group （F=1.546, P=0.215; F=2.107, P= 0.123）, while there was a significant difference for the ≥570 um group （F=5.396, P=0.006）. Differences among the groups using Bonferroni tests show that central corneal thickness （CCT） measured with Orbcan-II was significantly thicker than that obtained with the Pentacam （P=0.029） and uhrasonic pachymetry （P=0.010）. No statistically significant difference was found between measurements with Pentacam and ultrasonic pachymetry. Conclusion There are some differences in the three methods used to measure the CCT of patients before excimer laser myopic surgery, but overall there was no statistically significant difference, and the methods could be concordant in clinics. However, the three instruments still cannot completely replace one other. Key words: Corneal thickness ;  Ultrasonic pachymetry ;  Orbscan- II ;  Pentacam