Structure and Biomechanics of the Human Optic Nerve Head

描述（由申请人提供）：原发性开角型青光眼（POAG）是一种严重且日益严重的健康问题，约占全球失明的12%。研究已经确定年龄、祖籍群体（种族背景）和眼内压（IOP）是POAG发生和发展的重要危险因素。我们的长期目标是了解这些已确定的危险因素与视网膜神经节细胞的反应性丧失之间的关系，这是这种疾病的特征。目前的观点认为，视神经头（ONH）和网层（LC）的生物力学特性在确定POAG的病理中起着关键作用。在初步研究中，我们已经确定易受青光眼改变影响的LC区域（下、上）比LC的其他区域（鼻和颞）含有更少的胶原蛋白，并表现出更多的压力诱导变形（更柔顺）。在这些发现的基础上，本提案的目标是通过微观重建LC的结构成分和生物力学特性来定义ONH的三维生物力学特性，并将这些特性与POAG风险因素联系起来。根据我们的初步研究，我们提出以下可检验的假设：1)LC的结构和压力致变形存在区域差异，导致早期青光眼易感区域胶原减少，变形增加；2) LC结构和压力变形的区域差异随着年龄的增长而增大，并随祖先群的不同而变化，年龄越大、祖先越易发生POAG的个体结构变化越大、压力变形越大；3) LC结构和压力致变形的区域差异与三维微观弹性模量的差异直接相关，因此LC最易发生青光眼损伤的区域（与年龄和血统有关）的弹性模量与其他区域相比存在显著差异。为了验证这些假设，我们开发了创新的、最先进的技术，以高分辨率全面评估人类ONH的三维（3D）结构和生物力学特性。这些技术利用了已知的非线性光学效应，当超快激光产生的高强度光子与组织相互作用时，就会发生非线性光学效应。利用这些新技术，我们拟对正常人和不同祖先、不同年龄的离体人眼进行研究，其具体目的如下：1)利用人工压力室和超快激光在4个维度（时间和空间）动态映射IOP诱导的离体人眼胶原纤维和弹性纤维结构的变化；2)以高分辨率（0.9 mm横向和2mm轴向）三维重建ONH，以体积测量区域结构变化，并将其与同一眼内测量到的压力诱发变形相关联；3)测量离体人体ONH的局部（优势与劣势等）生物力学特性，将结构与生物力学特性和POAG易感性联系起来。我们期望这些研究将提供关于人类ONH的生物力学特性的新的、至关重要的信息，并提供对POAG危险因素的更清晰的理解。

DESCRIPTION (provided by applicant): Primary open angle glaucoma (POAG) represents a serious and growing health problem accounting for ~12% of global blindness. Studies have identified age, ancestral group (racial background), and intra- ocular pressure (IOP) as significant risk factors for the development and progression of POAG. Our long- range goal is to understand the relationship between these established risk factors and the responsive loss of retinal ganglia cells that characterizes this disease. Current wisdom proposes that the biomechanical properties of the optic nerve head (ONH) and lamina cribrosa (LC) play a critical role in defining the pathology of POAG. In preliminary studies, we have identified that regions of the LC susceptible to glaucomatous change (inferior, superior) contain less collagen and show more pressure-induced deformation (more compliant) than other regions of the LC (nasal and temporal). Building on these findings, the objective of this proposal is to define the 3 dimensional biomechanical properties of the ONH by microscopically reconstructing the structural components and biomechanical properties across the LC at a micron scale and relate these properties to POAG risk factors. Based on our preliminary studies we propose the following testable hypotheses:1) That there are regional differences in both the structure and pressure-induced deformation of the LC such that regions susceptible to early glaucomatous change have decreased collagen and increased deformation; 2) That the regional differences in LC structure and pressure-induced deformation increase with age and vary with ancestral group, such that older individuals and those with ancestries more susceptible to POAG will have greater structural changes and show greater pressure induced deformation; 3) That the regional differences in LC structure and pressure-induced deformation are directly related to differences in the 3 dimensional, microscopic elastic modulus such that regions of the LC most susceptible to glaucomatous damage (and related to age and ancestry) will have significant differences in the elastic modulus compared to other regions. To test these hypotheses, we have developed innovative, state of the art technologies to globally assess the three dimensional (3D) structure and biomechanical properties of the human ONH with high resolution. These technologies take advantage of known non-linear optical affects that occur when high intensity photons generated by ultrafast lasers interact with tissue. Using these novel technologies we propose to study ex vivo human eyes from normal individuals and different ancestries at varying ages by the following Specific Aims: 1) Dynamically map in 4 dimensions (time and space) IOP induced changes in collagen fibril and elastic fiber structure in ex vivo human ONH using an artificial pressure chamber and an ultrafast laser; 2) Three dimensionally reconstruct the ONH at high resolution (0.9 mm lateral and 2 mm axial) to volumetrically measure the regional changes in structure and relate these to the measured pressure induce deformations in the same eye; 3) Measure the regional (superior vs. inferior etc.) biomechanical properties of ex vivo human ONH to relate structure to the biomechanical properties and susceptibility to POAG. We expect that these investigations will provide new, and critically important, information concerning the biomechanical properties of the human ONH and provide a clearer understanding of the risk factors for POAG. PUBLIC HEALTH RELEVANCE: In this proposal, we will clarify the role of collagen and elastic components of the lamina cribrosa (LC) in the pathophysiology of axonal injury that occurs with aging and how it may be accelerated by increased IOP. We fully expect these data to lead to critically important information concerning the biomechanical properties of the human optic nerve head (ONH) and provide a clearer understanding of the risk factors for primary open angle glaucoma (POAG). To achieve our goal, we will use innovative, state of the art technologies based on ultrafast lasers that can produce two photon excited fluorescence for identifying elastin, second harmonic generated signals for identifying collagen and laser induced optical breakdown to probe the microscopic biomechanical properties using Acoustic Radiation Force Elastic Microscopy to globally assess the three dimensional structure and biomechanical properties of the ONH.