Significance: Corneal diseases is a major cause of reversible blindness in the world. Monitoring the progression of human corneal edema or corneal scarring to prevent the disease entering into the end stage is crucial. Aim: We present a method for sensing human corneal composition at different depths, namely focused on the epithelium and stromal layer, using high-sensitivity terahertz (THz) broadband spectroscopy. Approach: From the proposed methodology, the THz temporal and absorption spectra of human corneas at different edema stages have been studied. THz wave signals were collected from the direct reflection and four other collection points along the THz wave propagation direction as reviewed from the simulation THz electrical field. Result: Our results show that the epithelium layer acts as a good barrier to maintain hydration level of the stroma, and the quality of the epithelium can be used to predict the level of corneal swelling in corneal edema. At the detection points near to the incident point, the THz frequency spectra demonstrated interference oscillation behavior. At the final edema observing time, results showed that the epithelium lose its barrier properties. The intactness of the epithelium can be used to predict the edema severity in the final stage. When the detection points are further away from the incident point, the THz spectra are believed to contain information from stromal layer. Stromal absorption spectra demonstrated correlation with optical coherence tomography thickness results. Conclusion: The hydration concentration from stromal layer was further quantitatively calculated. At the end of the experiment, all the corneal hydration levels reach to the same value which shows that the edema hydration has reached maximum saturation. The information of individual sublayers of the cornea is obtained by characterizing noninvasively with the use of THz spectroscopy. To our knowledge, this is the first report of using THz for noninvasive characterization of sublayers of the cornea.

中文翻译：

---

人角膜亚层的太赫兹光谱分析

意义：角膜疾病是全球可逆性失明的主要原因。监测人角膜水肿或角膜瘢痕的进展以防止疾病进入终末期至关重要。目的：我们提出了一种使用高灵敏度太赫兹 (THz) 宽带光谱检测不同深度的人体角膜成分的方法，即聚焦于上皮和基质层。方法：根据所提出的方法，研究了人眼角膜在不同水肿阶段的太赫兹时间和吸收光谱。太赫兹波信号是从直接反射和沿太赫兹波传播方向的其他四个收集点收集的，如从模拟太赫兹电场中回顾的那样。结果：我们的结果表明，上皮层作为维持基质水化水平的良好屏障，上皮的质量可用于预测角膜水肿时角膜肿胀的程度。在靠近入射点的检测点，太赫兹频谱表现出干扰振荡行为。在最后的水肿观察时间，结果显示上皮失去了其屏障特性。上皮的完整性可用于预测最后阶段的水肿严重程度。当检测点远离入射点时，认为太赫兹光谱包含来自基质层的信息。基质吸收光谱证明与光学相干断层扫描厚度结果相关。结论：进一步定量计算基质层的水合浓度。在实验结束时，所有角膜水化水平达到相同的值，这表明水肿水化已达到最大饱和。角膜各个亚层的信息是通过使用太赫兹光谱进行非侵入性表征来获得的。据我们所知，这是第一次使用太赫兹对角膜亚层进行无创表征的报告。