Comparison of central corneal thicknesses measured by Orbscan II system and Ultrasonic pachymetry in myopia

Objective To evaluate the corneal thinknesses measured with Orbscan Ⅱ system and A-ultrasonic pachymetry.Methods Two hundred myopic subjects(400eyes) were recruited and divided into four groups according to the diopter and corneal thickness measured by A-ultrasonic pachymetry.Central corneal thicknesses(CCT) were measured with Orbscan Ⅱ topography system and A-ultrasonic pachymetry.Results The mean CCT by Orbscan Ⅱ system and A-ultrasonic pachymetry were(568.06±34.29) μm and(536.25±33.90) μm respertively.The result of Orbscan Ⅱ system was higher than that of A-ultrasonic pachymetry with a difference of(31.81±16.39) μm(P0.01).Firstly,The subjects were divided into four groups according to diopter:low myopia(-0.50～-3.00D),medium myopia(-3.25～-6.00D),high myopia(-6.25 ～9.00D)and supermyopia(-9.25～-15.00D),The results of Orbscan Ⅱ system were higher than those of A-ultrasonic pachymetry respectively(P0.01).Secondly,The subjects were divided into four groups based on the CCT measured by A-ultrasonic pachymetry :group1(≤500 μm),group 2(500～536 μm),group 3(536～572 μm),and group 4(≥572 μm).The results of Orbscan Ⅱ system were higher than those of A-ultrasonic pachymetry(P0.01).Conclusions There were significant differencees between the results of these two apparatus.The outcomes of Orbscan Ⅱ system are approximately 30 μm higher than those of A-ultrasonic pachymetry.Orbscan Ⅱ system cannot totally replace A-ultrasonic pachymetry.