Pentacam及OrbscanⅡ角膜地形图在可疑圆锥角膜的诊断特点分析

Comparison of Pentacam and Orbscan II systems for the diagnosis of keratoconus suspects

目的比较Pentacam及OrbscanⅡ在正常人及各期圆锥角膜的测量值及形态学特点，并进一步分析两者早期筛查可疑圆锥角膜的敏感性及有效性。方法选取正常人196只眼、可疑圆锥角膜50只眼、完成期圆锥角膜73只眼，分别行两种角膜地形图检查。观察角膜前、后表面曲率、最佳拟合球面（BFS）、I-S值（Inferior—Superior）（3及5mm）、高度图分类、高度值、角膜厚度等指标变化。采用单因素方差分析及秩和检验对数据进行统计学分析。结果Pentacam和OrbscanⅡ测量正常人角膜后表面的Kmax分别为（-6．5±0．2）、（-6．7±0．8）D，Kmin分别为（-6．0±0．9）、（-6．1±0．5）D，差异有统计学意义（Z=-10．5，-．1；P〈0．05）；其他如角膜前后表面BFS、高度值、厚度值等的测量值Pentacam也较小。高度图形态Pentacam正常组、可疑组均以递减为主，其递增型前表面分别为14．4％（28／196）及20．0％（10／50），后表面为2．0％（4／196）及26．0％（13／50）；完成期组前表面91．7％（67／73）、后表面94．5％（69／73）为递增型。Orbscan正常组80．4％（165／196）递增型，可疑、完成期圆锥角膜组全递增型。ROC曲线敏感指标及cutoff值：Orbscan角膜前、后表面I—s值（3mm及5mm）对可疑圆锥角膜的诊断灵敏，角膜前表面5mm的cutoff值为1．15D，后表面为0．65D。Pcntacam除I-S值敏感外，角膜前、后表面高度值亦具良好的诊断价值；角膜前表面高度cutoff值4．5μm，角膜后表面7．5μm。结论两仪器在正常人多个指标差异有统计学意义，Pentacam数值小。两仪器I—s值对可疑圆锥角膜筛查灵敏，而结合高度图形态及高度值Pentacam诊断价值更高，高度图递增型角膜前突危险增大。

Objective To compare the sensitivity of Pentacam and Orbscan Ⅱ and to analyze the morphology characteristic of topography in normal eyes and different stages of keratoconus, to provide the basis for early screening of keratoeonus suspects. Methods One hundred and ninety six normal eyes, 50 eyes with keratoconus suspect and 73 eyes with clinical keratoconus were enrolled. The changes of corneal anterior/posterior curvature, best fitting sphere （BFS）. Inferior-Superior value （I-S） （3 mm and 5 ram） , classification of elevation maps and corneal thickness were measured. Results There were significant differences including posterior curvature, anterior/posterior BFS, elevation value and corneal thickness in normal eyes between the data measured by these two different instruments, values obtained by Pentacam were less than those by OrbscarL Concerning the elevation maps pattern, the progressively decreasing pattern was dominant in Pentacam with normal eyes and keratocomus suspects, with the progressively increasing pattern accounting for 14. 4% （28/196） and 20. 0% （10/50） respectively in anterior surface, and 2. 0% （41/96） and 26. 0% （13/50） in posterior surface. The progressively increasing pattern was in dominant with clinical keratoeonus, accounting for 91.7% （67/73） and 94.5% （69/73） respectively in anterior and posterior surface. Progressively increasing pattern in Orbsean was presented in 80. 4% （165/196） normal eyes and suspected or clinical stage keratoconus. As to the receiver-operating-characteristic （ROC） curves and cutoff value, Orbsean I-S value （3 mm and 5 mm） of anterior and posterior surface was sensitive for the diagnosis of keratoconus suspects, with the cutoff value of anterior and posterior 5 mm I-S at 1. 15 D and 0. 65 D, respectively. In addition to the sensitivity of I-S values in Pentacam, the elevation value of anterior and posterior surface also displayed important diagnostic meaning. The cutoff of anterior, posterior elevation values was 4. 5 μm and 7.5 μm, respectively. Conclsuions Numerous measured indicators revealed obviously difference between the two instruments in normal eyes, with slightly smaller values in Pentacam. In addition to I-S values, pattern changes and elevation values in elevation map of Pentacam represent remarkable advantages for the screening of keratoconus suspects. There is an incremental risk of corneal ectasia in the increasing pattern of elevation map.