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C.R. Ethier, I.A. Sigal, I. Tertinegg, J.G. Flanagan; Optic Nerve Head (ONH) Deformation and Biomechanics Studied by Finite Element Modeling . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1091.
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Purpose: Retinal ganglion cell loss in glaucomatous optic neuropathy is hypothesized to be due in part to mechanical damage to axons at the level of the lamina cribrosa. Our goal was to quantify the biomechanical environment within the ONH as part of a program to study biomechanical factors in the pathogenesis of glaucoma. Methods: A computer model of the ONH was created, consisting of four components: sclera, lamina cribrosa, pre-laminar nerve tissue, and post-laminar nerve tissue. Tissues were assumed to be incompressible, isotropic and linearly elastic, and were assigned Young’s moduli of 3 MPa, 0.3 MPa, 0.03 MPa and 0.03 MPa, respectively. Tissue deformation in response to different IOP levels was computed using the finite element technique as implemented in a commercial code (ANSYS). Computed deformations of the vitreo-retinal interface were compared with Heidelberg Retinal Tomographic measurements in enucleated human eyes. Results: Peak von Mises strains (% deformation) in the lamina cribrosa were approximately 15% as IOP increased from 15 to 50 mmHg. There was a notable strain concentration at the termination of Bruch’s membrane. The pre-laminar nerve tissue showed significant deformation, including lateral cup enlargement. The magnitude of deformation of the vitreo-retinal interface was consistent with that seen experimentally in normal eyes. The shape of the deformation was also consistent with average topography differences seen between normal and glaucomatous eyes (Swindale et al., IOVS, 2000). Maximal posterior displacement of the anterior retinal surface occurred on the floor of the optic cup, but not at the centre of the optic cup. Conclusions: Strain levels in the lamina cribrosa are biologically significant. Acute patterns of ONH deformation in response to IOP changes are consistent with long-term changes observed in glaucoma patients (Swindale et al.). Surprisingly, the deformation of the vitreo-retinal interface is significantly influenced by deformation of the pre-laminar nerve tissue and is only indirectly related to the deflection of the underlying lamina cribrosa.
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