Zernike多项式分析全角膜前后表面和厚度三维不规则分布在圆锥角膜诊断中的价值

Zernike polynomial analysis of corneal tomography and anterior and posterior corneal topography in the diagnosis of keratoconus

目的评价利用Zemike多项式分析全角膜前后表面和厚度三维不规则分布在圆锥角膜中的诊断作用。方法病例对照研究。选取圆锥角膜患者20例（30眼）作为圆锥角膜组和同期健康志愿者30例（30眼）作为正常对照组。应用Pentacam系统测量所有受试者的眼前节形态，记录角膜前后表面高度以及全角膜厚度数据。利用Zemike多项式分析得出2～7阶和高阶系数的均方根（RMS）值。采用独立样本t检验对参数进行统计比较，通过受试者工作特征曲线（ROC）对测量参数的诊断性能进行评估。结果经Zemike多项式分析处理后的2～7阶和高阶系数的RMS值在圆锥角膜组和正常对照组中的差异均有统计学意义（P〈0．001）。角膜前表面高度参数中，以3阶、5阶和高阶系数的RMS值对圆锥角膜的诊断性能较好，曲线下面积（AUC）分别为0．999、0．982、0．994：在角膜后表面高度参数中，以3阶、5阶、7阶和高阶系数的RMS值对圆锥角膜的诊断性能较好，AUC分别为0．997、0．991、0．993、0．981；在全角膜厚度参数中，以3阶、5阶和高阶系数的RMS值对圆锥角膜的诊断性能较好，AUC分别为0．993、0．989、0．992。其中3阶系数的RMS值诊断圆锥角膜的性能最好，在角膜前后表面高度和全角膜厚度中，其AUC均接近1．000。结论基于Pentacam系统的Zemike多项式分析全角膜前后表面高度和厚度三维不规则分布在圆锥角膜的诊断中有一定的临床指导价值。以3阶系数的RMS值诊断性能最高。

Objective To analyze corneal tomography and anterior and posterior corneal topography by Zemike polynomial fitting in the diagnosis of keratoconus. Methods Keratoconus patients （n=20, 30 eyes） and normal subjects （n=30, 30 eyes） were recruited for this case-controlled study. The Pentacam system was used to gather pachymetry data of the entire cornea and the elevations of the anterior and posterior corneal surfaces. Zernike polynomial fitting was used to quantify the 3D distribution of the corneal anterior and posterior surface elevations and thickness to obtain the root mean square （RMS） values for 2nd to 7th order and the higher-order aberration （HOA）. Statistical analysis methods included independent samples t-test and receiver operating characteristic （ROC） curves. Results The 2nd to 7th order and the HOA RMSs of the anterior and posterior surface elevation and pachymetry were significantly different in the keratoconus patients compared to the normal subjects （P〈0.001）. Among the corneal anterior surface elevation and pachymetry parameters, the 3rd, 5th, and HOA RMSs had high diagnostic accuracy. The areas under the ROC curves for anterior surface elevation were 0.999, 0.982, 0.994, and for pachymetry they were 0.993, 0.989, 0.992. The 3rd, 5th, 7th, and HOA higher-order RMSs of the corneal posterior surface elevation also had high diagnostic accuracy. The areas under the ROC curves were 0.997, 0.991, 0.993, 0.981. Among these parameters, the 3rd RMS for the corneal posterior surface elevation had the highest diagnostic accuracy with an area under the ROC curve of almost 1.000. Conclusion Based on Pentacam images to assess the characteristics of the entire corneal topography and tomography, the Zernike polynomial application, especially the 3rd RMS values, had good accuracy in the diagnosis of keratoconus.