Corneal pachymetry measurement with ORBSCAN-II Topography System vs ultrasonic pachymetry

Objective:To evaluate corneal thickness measurement with Orbscan Ⅱ topography System vs ultrasonic pachmetry,try to find out the regularity of the difference between them.Method:The central corneal thickness of 222 patients (423 eyes) with simple refractive errors were measured with Orbscan Ⅱ topography system and ultrasonic pachymetry.The results were treated statistically and the differences were analysed.Results:Of the 423 eyes,the central corneal thickness measured with A scan was (544 52±32 43) μm,and that with Orbscan Ⅱ,(515 39±35 77)μm.The difference between them was significant (P0 05).The difference of the results between these two methods was -18～64μm,with a mean value (29 15±13 61) μm,and 54 38% was between 20～40μm.The difference in 2 eyes (0 47%) was ≥60μm;in 26 eyes (6 15%) 50～59 μm,in 65 eyes (15 37%) 40～49 μm,in 126 eyes (29 79%) 30～39 μm,in 104 eyes (24 59%) 20～29 μm,in 67 eyes (15 84%) 10～19 μm,in 24 eyes (5 67%) 0～9 μm,and 9 eyes (2 13%) less than 0 μm.Conclusion:When to measure the central corneal thickness,the value obtained with Orbscan Ⅱ topography was lower than that with ultrasonic pachymetry about 20～40 μm.Ultrasonic pachymetry is still the most accurate method in corneal pachymetry.