IEEE Trans Med Imaging. 2018 Nov;37(11):2463-2473. doi: 10.1109/TMI.2018.2836304. Epub 2018 May 15.
Identification of objective criteria to correctly diagnose ectatic diseases of the cornea or to detect early stages of corneal ectasia is of great interest in ophthalmology and optometry. Metrics for diagnosis typically employed are curvature maps (axial/sagittal, tangential); elevation map of the anterior surface of the cornea with respect to a reference sphere; and pachymetry (thickness) map of the cornea. We present evidence that currently used curvature maps do not represent the actual curvatures (principal or mean) in a human cornea. A novel contribution of this paper is the computation of the true mean curvature over every point of a central region of the cornea. We show that the true mean curvature can accurately identify the location of the ectasia. We present a quartic smoothing spline algorithm for the simultaneous computation of elevation maps for anterior and posterior corneal surfaces, pachymetry, and true mean curvature. The input to the algorithm is data from a single measurement from imaging devices such as an anterior segment optical coherence tomographer or a Scheimpflug imager. We show that a different combination of metrics is useful for the diagnosis of existing ectasia (true mean curvature and anterior elevation map) as opposed to subclinical ectasia (pachymetry and posterior elevation map). We compare our results with existing algorithms, and present applications to a normal cornea, a forme fruste keratoconic cornea, and an advanced keratoconic cornea.
在眼科和视光学中，准确诊断角膜扩张性疾病或早期发现角膜扩张症具有重要意义。用于诊断的典型指标包括曲率图（轴向/矢状，切向）；角膜前表面相对于参考球面的高度图；以及角膜厚度图。我们提供的证据表明，目前使用的曲率图不能代表人眼角膜的实际曲率（主曲率或平均曲率）。本文的一个新贡献是计算角膜中央区域每个点的真实平均曲率。我们表明，真实平均曲率可以准确识别扩张的位置。我们提出了一种四次样条平滑算法，用于同时计算前、后角膜表面的高度图、角膜厚度和真实平均曲率。该算法的输入是来自成像设备（如前节光学相干断层扫描仪或 Scheimpflug 成像仪）的单次测量数据。我们表明，对于现有的扩张症（真实平均曲率和前表面高度图）与亚临床扩张症（角膜厚度和后表面高度图）的诊断，不同的指标组合是有用的。我们将我们的结果与现有的算法进行了比较，并展示了对正常角膜、轻度圆锥角膜和晚期圆锥角膜的应用。
