The Biomechanics of the Human Lamina Cribrosa and Posterior Sclera: Effects of Age and Glaucoma

Johns Hopkins University, Baltimore MD

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Abstract

? DESCRIPTION (provided by applicant): Glaucoma is a leading cause of blindness in the United States, and the second leading cause worldwide. There is consensus that the level of intraocular pressure generates a biomechanical response in the tissues of the optic nerve head that is fundamental to the early events in glaucoma damage. The level and state of stress and strain in the optic nerve head are determined by the mechanical properties of the posterior sclera and lamina cribrosa and how they differ. Mechanical stresses and deformation of the optic nerve head can damage the retinal ganglion cell axons both directly and indirectly through mechanical activation of the lamina cribrosa cells and disruption of blood ?ow from the distortio of blood vessels. We hypothesize that the biomechanical interaction of the sclera and lamina cribrosa is central to the development glaucomatous optic neuropathy. To investigate this hypothesis, we will develop in Aim 1 an innovative microscopic in?ation experiment to measure the local deformation response of the lamina cribrosa of human post-mortem eyes, and examine the effects of scleral behavior measured for the same eye, age, and glaucoma stage. In Aim 2, we will separate the contributions of the extracellular matrix components by measuring changes to the pressure-induced deformation behavior of the lamina cribrosa cause by chemical modi?cations, either stiffening or softening, of only the sclera or of the sclera and lamina cribrosa. We will measure the collagen and elastin structure of the lamina cribrosa in Aim 3 and evaluate for the effects of the scleral ?ber structure measured for the same eye, age, and glaucoma stage. Aim 4 will integrate the data gathered from the mechanical and structural experiments in computational models of the lamina cribrosa and sclera to study the relationship between microstructure and mechanical properties of the tissues. The proposed Aims will advance both the fundamental scienti?c understanding of the pathogenesis of glaucoma and the development of new diagnostic and neuroprotection strategies. The outcomes of Aim 1 will provide the physiological and pathological levels of mechanical stimuli to the tissues of the op- tic nerve head for studies of blood ?ow and mechanical activation of lamina cribrosa cells. The outcomes of Aim 2 will measure the effect of selective scleral stiffening or softening on the stresses and strains in the optic nerve head, thus will guide the development of new scleral neuroprotection strategies. Aims 3 and 4 will provide an understanding of the relationship between the microstructure and mechanical behavior of the lamina cribrosa. This will allow us to predict features that can be identi?ed as biomechanical markers in in vivo optical coherence tomography imaging for new diagnostic strategies. The proposed work will provide the ?rst study of the biomechanics of the lamina cribrosa and the peripapillary sclera in relation to each other in the same eye. It will also provide the ?rst detailed measurements of the effect of selective scleral stiffening and softening on the strain state of the optic nerve head.