Noninvasive 3D Microscopic Studies of Corneal Elasticity and Collagen Structure

描述（申请人提供）：角膜生物力学在决定眼睛的结构完整性、光功率和整体视觉质量方面起着重要作用。常见的表现为角膜生物力学异常的情况，如圆锥角膜和lasik后扩张，影响数百万人，通常需要角膜移植。角膜生物力学在治疗性和屈光性角膜手术的术后结果中也发挥着越来越重要的作用，影响着最终视力结果的可预测性、质量和稳定性。增加我们对角膜生物力学如何控制角膜稳定性和屈光的理解的一个关键限制是缺乏显微镜下测量角膜结构和局部生物力学特性的非侵入性技术，例如三维空间内的角膜弹性。我们假设，通过测量飞秒激光产生的空化气泡与声辐射力相互作用时的运动，我们可以在不改变其结构和功能的情况下确定单个角膜的杨氏模量的局部值。我们还假设角膜的不均匀弹性特性受到胶原层微观结构组织的强烈影响，并且具有异常生物力学的角膜也可能与角膜层的异常组织有关。最后，我们假设基于特定角膜的弹性和微观结构数据，可以构建准确描述和预测其生物力学行为的特定有限元模型（FEM）。为了验证我们的假设，我们计划开发一种基于气泡的声辐射力弹性显微镜（ARFEM），并表明它可以无创地用于开发高分辨率的3D角膜弹性图。然后，我们将把角膜弹性的局部变化与基于飞秒激光的二次谐波成像显微镜（SHIM）观察到的微观结构联系起来。我们还将用ARFEM和SHIM研究生物力学紊乱的角膜，并将其弹性图与微观结构观察相关联。我们将基于实测的ARFEM和SHIM数据构建有限元模型，并证明该模型能准确预测特定角膜的生物力学行为。最后，我们将在活兔模型中证明，ARFEM和SHIM都可以安全地在体内进行，而不会对组织造成损伤或对眼睛产生有害影响。本课题的成功完成将为在体内无创测量角膜弹性图谱和微观结构提供实验依据。这也将为角膜弹性受胶原结构影响的理论提供支持，并为ARFEM和SHIM表征的角膜生物力学行为可以通过个体化有限元模型准确预测提供支持。该项目的研究结果将增加我们对角膜生物力学及其对胶原结构的依赖性的理解，并可能为诊断、预防或治疗日益常见的角膜疾病（如圆锥角膜和lasik后扩张）提供新的工具。公共卫生相关性：我们介绍了新的无创方法来定义单个角膜的弹性特性和胶原结构的空间分布。健康眼睛的这些功能和结构测量的相关性将与那些患有常见角膜疾病（如圆锥角膜和lasik术后扩张）或有这些疾病风险的人进行比较。该项目的结果将提高我们对角膜生物力学及其对胶原结构的依赖性的理解，为数百万因这些疾病而面临严重视力丧失风险的人提供新型诊断仪器和最终治疗方式的基础。

DESCRIPTION (provided by applicant): Corneal biomechanics plays an important role in determining the eye's structural integrity, optical power and the overall quality of vision. Common conditions that manifest abnormal corneal biomechanics, such as keratoconus and post-LASIK ectasia affect millions of people and often necessitate corneal transplantation. Corneal biomechanics also plays an increasingly recognized role in the post-operative results of therapeutic and refractive corneal surgery procedures, affecting the predictability, quality and stability of final visual outcomes. A critical limitation to increasing our understanding of how corneal biomechanics controls corneal stability and refraction is the lack of non-invasive technologies that microscopically measure the corneal structure and local biomechanical properties, such as corneal elasticity within the 3D space. We hypothesize that by measuring the movement of a femtosecond laser generated cavitation bubble as it interacts with an acoustic radiation force, we can determine local values for an individual cornea's Young's modulus, without altering its structure and function. We also hypothesize that the inhomogeneous elastic properties of the cornea are strongly influenced by the microstructural organization of collagen lamellae, and that corneas with abnormal biomechanics also may be associated with an abnormal organization of corneal lamellae. Finally, we hypothesize that based on the elasticity and microstructural data for a particular cornea, a specific finite element model (FEM) can be constructed that accurately describes and predicts its biomechanical behavior. To test our hypothesis we plan to develop a bubble-based, acoustic radiation force elastic microscope (ARFEM) and show that it can be used noninvasively to develop a high resolution 3D corneal elasticity map. We will then correlate local variations in corneal elasticity with the microstructure observed by femtosecond laser based second harmonic imaging microscopy (SHIM). We will also investigate biomechanically disordered corneas with both, ARFEM and SHIM, and correlate their elasticity maps with microstructural observations. We will construct a FEM based on the measured ARFEM and SHIM data and show that this model accurately predicts biomechanical behavior for a particular cornea. Finally we will demonstrate in a live rabbit model, that both, ARFEM and SHIM can be performed safely in vivo without tissue damage or harmful effects to the eye. The successful completion of this project will provide experimental evidence that corneal elasticity maps and microstructure can be measured in vivo noninvasively. It will also provide support for the theory that corneal elasticity is influenced by the collagen microstructure, and that the biomechanical behavior of a cornea characterized by ARFEM and SHIM can be accurately predicted by individualized finite element modeling. The results of this project will increase our understanding of corneal biomechanics and its dependence on collagen microstructure and may provide the basis for a novel tool that could be helpful in diagnosing, preventing or treating increasingly common corneal diseases such as keratoconus and post-LASIK ectasia. PUBLIC HEALTH RELEVANCE: We introduce novel noninvasive methods to define spatial distribution of elastic properties and collagen microstructure of individual corneas. The correlation of these functional and structural measurements in healthy eyes will be compared with those that either have common corneal disorders (such as keratoconus and post-LASIK ectasia), or are at risk for them. The results of this project will improve our understanding of corneal biomechanics and its dependence on the collagen microstructure, providing a basis for novel diagnostic instruments and eventual therapeutic modalities for the millions of people that are at risk for severe visual loss from these conditions.