Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
Institute of Applied Physics, Vienna University of Technology, Vienna, Austria.
Invest Ophthalmol Vis Sci. 2018 Nov 1;59(13):5579-5588. doi: 10.1167/iovs.18-25311.
We demonstrate segmentation and mapping of corneal layers (epithelium, Bowman's layer, and stroma) across the entire cornea (limbus to limbus), using additional contrast provided by polarization-sensitive optical coherence tomography (PS-OCT) and analyze the reproducibility of the procedure.
A custom built PS-OCT system operating at 1045 nm central wavelength with conical scanning was used for image acquisition. Conical scanning allows for almost perpendicular beam incidence on the corneal surface and provides good signal quality over the entire field of view. Epithelium, Bowman's layer, and stroma were segmented using the additional contrast provided by PS-OCT. Thickness maps were computed and analyzed in sectors. Both eyes of 20 healthy volunteers were imaged at least three times to test this method and to quantify reproducibility.
Thickness maps of the epithelium show significant (P < 0.001) superior thinning and an inferior thickening. Bowman's layer appears homogeneous within the central 7 to 8 mm diameter of the cornea and gets thinner toward the periphery until this layer disappears between 4 and 5.5 mm eccentricity from the center. Intersubject variations of the measured thicknesses of epithelium (coefficient of variation [CV] ∼8%), Bowman's layer (CV∼25%), and stroma (CV∼10%) were observed. Very good reproducibility of thickness measurements of epithelium (CV < 3%), Bowman's layer (CV < 5%), and stroma (CV < 2%) was found. Furthermore, a significant correlation (P < 0.001) between layer thicknesses of the right and left eyes of the same subject was found.
PS-OCT with conical scanning is a feasible approach for determining thickness maps of corneal layers on a large field of view with high reproducibility.
我们使用偏光敏感光学相干断层扫描（PS-OCT）提供的额外对比度，演示整个角膜（从角膜缘到角膜缘）的角膜层（上皮、Bowman 层和基质）的分割和映射，并分析该过程的重现性。
使用在 1045nm 中心波长下工作的定制 PS-OCT 系统进行图像采集。圆锥扫描允许光束几乎垂直入射到角膜表面，并在整个视场中提供良好的信号质量。使用 PS-OCT 提供的额外对比度对上皮、Bowman 层和基质进行分割。计算并分析了扇区的厚度图。对 20 名健康志愿者的双眼进行了至少三次成像，以测试该方法并量化其重现性。
上皮的厚度图显示出明显的（P<0.001）上变薄和下变厚。Bowman 层在角膜中央 7 到 8mm 直径范围内呈现均匀性，并向周边变薄，直到在离中心 4 到 5.5mm 的偏心处该层消失。测量的上皮厚度（变异系数 [CV]∼8%）、Bowman 层（CV∼25%）和基质（CV∼10%）的个体间变化。上皮（CV<3%）、Bowman 层（CV<5%）和基质（CV<2%）的厚度测量具有非常好的重现性。此外，还发现同一受试者右眼和左眼的层厚度之间存在显著相关性（P<0.001）。
圆锥扫描的 PS-OCT 是一种可行的方法，可以在大视场中具有高重现性地确定角膜层的厚度图。
