This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.Permanent posterior cupping of the optic nerve head (ONH) is the chief clinical hallmark of Glaucoma. In order to advance the hypothesis that the structure of an individual nerve head determines the damage-causing level of intra ocular pressure (IOP) parallel finite element computations of the stresses and strains are carried out on micron-scale voxel based reconstructions of the lamina (connective tissue in the ONH) from monkeys. The work begins with refinements to the computational scheme followed by testing of the two approaches to applying the IOP load on the lamina from a normal monkey eye: (a) Via a linear translaminar gradient in pressure on the lamina, (b) Via a fixed pressure equal to the IOP anteriorly on (elastically weak) tissue anterior to and filling the pores within the lamina that model neural tissue. In addition to pressure loading the boundary of the lamina is stretched by interpolating displacements from 'continuum' finite element computations done for the posterior pole (halfglobe including the ONH) with large elements with regionalized elastic constants. The continuum computations use the experimental estimate of global anterior-to-posterior laminar deformation as a fitting parameter to determine the overall scale of the elastic constant. Comparing the elastic constant derived from the voxel-based computations for a similar fit to that derived from the continuum computations a validation/standardization of the IOP loading procedure is attempted: The smaller value of elastic constant derived from (a), that is argued as being due to the reduction in the total anterior-to-posterior force derived from a pressure gradient, suggests that (b) is the validated procedure as it predicted the same value of elastic constant.
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