Orbscan角膜地形图系统测量误差的分析

目的：探讨Orbscan角膜地形图系统（Orbscan系统）的测量误差及其影响因素,为临床使用提供依据。方法：使用Orbscan系统和A超仪,测量200例（400只眼）行准分子激光原位角膜磨镶术（laser in situ keratomileusis,LASIK）患者和50例（100只眼）行准分子激光屈光性角膜切削术（photorefractive keratectomy,PRK）患者手术前、后的角膜厚度和中央前房深度;分别于PRK和LASIK手术前、后使用Orbscan系统测量患者的角膜后表面屈光力,并对测量值进行分析比较。结果：Orbscan系统测量的角膜厚度值LASIK和PRK术前低于A超仪的测量值,差值为18.83-24.29μm;LASIK和PRK术后与A超仪测量值的差值为56.32-139.52μm,明显高于术前。LASIK和PRK手术前、后Orbscan系统测量的中央前房深度值与A超仪测量值的差值为0.16-0.25mm,无临床意义。LASIK手术前、后Orbscan系统测量的角膜后表面屈光力差值约为-0.60D;PRK手术前、后Orbscan系统测量的角膜后表面屈光力差值低度组为-0.51D,中度组为-1.12D。结论：Orbscan系统测量值的精确性尚待进一步提高;LASIK和PRK术后角膜雾状混浊和角膜前表面屈光力的改变是导致Orbscan系统测量误差较大的主要原因;Orbscan系统的测量误差是临床工作不可忽视的重要问题。

An analysis of measurement error in Orbscan topography system

OBJECTIVE: To discuss the measurement error and the influence factor of Orbscan Topography to provide more accurate data for clinical application. METHODS: Orbscan Topography System and A-scan ultrasonography were used to measure the corneal thickness and anterior chamber depths pre-operatively and post-operatively, including 200 cases (400 eyes) undergoing laser in situ keratomileusis (Lasik) and 50 cases (100 eyes) undergoing photorefractive keratectomy (PRK). The curvature of posterior corneal surface was measured by Orbscan topography before and after the operations, and the result of measurement was compared. RESULTS: Pre-operatively, the value of corneal thickness was (18.83 - 24.29) microm lower measured by Orbscan topography than that by A-ultrasonography, and post-operatively the value was (56.32 - 139.52) micro m lower than that by A-ultrasonography. The postoperative value was obviously higher than the pre-operative one. The value of central anterior chamber depth was (0.16 - 0.25) mm lower measured by Orbscan system than that by A-ultrasonography pre-operatively and post-operatively. There was no clinical significance. The difference in the comparison of posterior corneal surface curvature before and after Lasik was -0.60 D measured by Orbscan System. The difference in the comparison of posterior corneal surface curvature before and after PRK was -0.51 D in the lower diopter group and -1.12 D in medium diopter group. CONCLUSIONS: It is necessary to improve the accuracy of Orbscan Topography System. The Haze and the change of anterior corneal surface curvature after Lasik and PRK are the main causes of measurement error in Orbscan Topography System. Clinically, it is an un-negligible important problem in the measurement of Orbscan system.