Determining the Efficacy of Corneal Cross-Linking Protocols using Brillouin Microscopy

摘要： 圆锥角膜及其相关的角膜扩张性疾病导致生活质量显著下降， 在美国，这是全层角膜移植的原因，并且比以前认为的要普遍得多。 角膜交联（CXL）已成为一种通过硬化来阻止圆锥角膜进展的临床技术 角膜基质。尽管在临床上使用了十多年，但目前无法评估 CXL方案的疗效或预测长期稳定性，因为我们缺乏定量的生物力学指标 为预测模型提供信息。目前可用的表征CXL反应的指标是形态学的， 不能预测临床结果。主要的差距是缺乏测量技术， 准确和非扰动地表征具有三维（3-D）分辨率的角膜力学， vivo.为了满足这一需求，在过去的十年里，我们开创了布里渊显微镜，一种高分辨率的光学显微镜。 该技术可以在不接触或干扰眼睛的情况下以3D方式原位测量角膜纵向模量。 布里渊显微镜提供了第一个也是唯一的直接力学证据，表明在低应变条件下， 圆锥角膜在体内和CXL诱导的角膜硬化的唯一3-D地图。这个项目的总体目标是 研究计划是将联合收割机3-D布里渊角膜图和有限元（FE）建模相结合， 预测CXL方案后的角膜形状结局。在强有力的初步数据中，我们证明， 考虑到组织水化，我们可以建立布里渊测量之间的定量关系， 纵向模量和杨氏模量。因此，我们的中心假设是角膜杨氏的空间图 从定量布里渊显微镜导出的模量将使得能够准确预测角膜形状行为 通过FE建模。这种非侵入性测量角膜硬度的方法的发展也使我们能够使用 第一次，在纵向研究中， 体内，使用无法在人体中进行的实验方案通过直接机械分析进行验证 科目我们将通过以下三个具体目标来检验我们的中心假设：1）测量体内布里渊 CXL后的机械测量; 2）量化新型CXL方案的体内机械结果;以及 3)通过布里渊成像和FE建模将CXL生物力学影响与形态学结局联系起来。这 研究是重要的，因为准确的无损，非扰动弹性为基础的指标将推动一个 CXL方案如何在临床上以及最终进行评估、开发和执行的范式转变 使我们能够制定个性化的CXL治疗方案。

ABSTRACT: Keratoconus and related corneal ectatic diseases cause significantly decreased quality of life, are the leading cause for full thickness corneal transplant in the US, and are significantly more prevalent than previously thought. Corneal cross-linking (CXL) has emerged as a clinical technique to halt keratoconus progression by stiffening the corneal stroma. Despite being used clinically for more than a decade, it is currently impossible to assess CXL protocol efficacy or predict the long-term stability and because we lack quantitative biomechanical measures to inform predictive models. Currently available metrics to characterize CXL responses are morphologic and have not proven predictive of clinical outcomes. The major gap is the lack of measurement techniques that can accurately and non-perturbatively characterize corneal mechanics with three-dimensional (3-D) resolution in vivo. To address this need, in the past decade we have pioneered Brillouin microscopy, a high-resolution optical technology that can measure corneal longitudinal modulus in situ in 3-D without contacting or perturbing the eye. Brillouin microscopy has provided the first and only direct mechanical evidence of decreased modulus in keratoconus corneas in vivo and the only 3-D maps of CXL-induced corneal stiffening. The overall goal of this research program is to combine 3-D Brillouin corneal maps and finite element (FE) modeling to quantitatively predict corneal shape outcomes after CXL protocols. In strong preliminary data, we demonstrated that, by accounting for tissue hydration, we can establish the quantitative relationship between Brillouin-measured longitudinal modulus and Young’s modulus. Thus, our central hypothesis is that spatial maps of corneal Young’s modulus derived from quantitative Brillouin microscopy will enable accurate prediction of corneal shape behavior via FE modeling. The development of this noninvasive measure of corneal stiffness also enables us to use a rabbit model to evaluate, for the first time, both morphologic and mechanical evolution in longitudinal studies in vivo, validated by direct mechanical analysis using experimental protocols that cannot be performed in human subjects. We will test our central hypothesis through the three specific aims: 1) Validate in vivo Brillouin mechanical measurements after CXL; 2) Quantify the in vivo mechanical outcomes of novel CXL protocols; and 3) Link CXL biomechanical impact to morphologic outcome with Brillouin imaging and FE modeling. This research is significant because accurate nondestructive, nonperturbative elasticity-based metrics will drive a paradigm shift in how CXL protocols are evaluated, developed, and performed clinically as well as ultimately allow us to develop individualized CXL treatment protocols.