Comparison Of Central Corneal Thickness Measured By Orbscan â…¡ System, Specular Microscopy And Ultrasonic Pachymetry In Myopia

Objective To evaluate the veracity of Orbscan Ⅱ system, specular microscopy in measuring central corneal thickness(CCT) compared with ultrasonic pachymetry. Methods CCT was measured in 650 eyes of 650 myopic patients with above three systems. The data were analyzed by T-test, linear regression and correlation. Results The mean CCT of Orbscan Ⅱ system, specular microscopy and ultrasonic pachymetry were 536.03±43.83μm,561.48±40.30μm and 532.62±38.59μm respectively. The results of Orbscan Ⅱ system and specular microscopy were both higher than ultrasonic pachymetry and the differences were 3.411±14.96μm and 28.88±29.84μm respectively(p<0.01).The subjects were divided into 4 groups based on the CCT measured by ultrasonic pachymetry:group1(=490μm),group2(490～ 540μm),group3 (540～590μm) group4(>590μm).The CCT of Orbscan Ⅱ system measurement were 6.66±16.82μm thinner than ultrasonic pachymetry in group 1 (t=3.74,p<0.01),while the CCT measured by Orbscan Ⅱ system were thicker in other groups (t=5.09,6.49,3.72, p<0.01) .The CCT measured by specular microscopy were thicker than ultrasonic pachymetry in all groups (p<0.01). Conclusions The outcomes of Orbscan Ⅱ system in measuring CCT are comparable to ultrasonic pachymetry measurement. Thus Orbscan Ⅱ system can be used as a veracious corneal pachymetry in normal subjects. But the readings are lower than ultrasonic pachymetry when the CCT is under 490μm and higher when the CCT is up to 590μm.The outcomes of specular microscopy are approximately 30μm higher than ultrasonic pachymetry, the consistency between these two methods increase when the CCT is thicker.