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J. Downs, M. D. Roberts, C. F. Burgoyne, R. T. Hart; Finite Element Modeling of the Lamina Cribrosa Microstructure in Normal and Early Glaucoma Monkey Eyes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3301.
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© ARVO (1962-2015); The Authors (2016-present)
To estimate intraocular pressure (IOP)-related strain within regions of the lamina cribrosa microstructure using finite element (FE) analysis.
3D reconstructions (2.5 x 2.5 x 3.0 µm/voxel) were constructed of the optic nerve head (ONH) from both eyes of 3 monkeys (1 eye normal (N), 1 eye early glaucoma (EG), both perfusion-fixed at an IOP of 10 mm Hg) [IOVS, 2004; 45:4388]. 3D, macro-scale continuum FE models of each individual ONH and posterior scleral shell were constructed in which IOP was increased from 10 to 45 mm Hg and the resultant displacement, stress and strain were calculated. The laminar elastic modulus was adjusted such that each continuum model’s laminar displacement matched histologic displacements for N and EG eyes. The 3D-segmented laminar microstructure [IEEE Trans Med Imag, 2006; 25:245] within 4 macro-scale continuum elements from the mid-periphery of each ONH model was surfaced, smoothed and converted into micro-scale FE models of the individual laminar beams in that region. Isotropic material properties derived from the parent continuum model were applied to all micro-FE model elements. Displacements of the parent continuum element were applied as loadings on the micro-FE models at all nodes coincident with the parent element’s faces. Resultant maximum principal strains (MPS) in each micro-FE model were sorted by magnitude, separated into 20 bins of equal volume, and plotted for comparison.
For an IOP increase from 10 to 45 mm Hg, mean laminar MPS (local % stretch) varied substantially within individual beams and by quadrant, with the highest MPS in the superior quadrant in the N eyes and the nasal or inferior quadrants of the EG eyes. MPS averaged 4.1, 3.0, and 2.3% in the EG eyes as compared to 7.6, 2.4, and 2.6% in their contralateral N controls, respectively.
These data suggest that the highest laminar strains shift from the superior quadrant in N eyes to the nasal/inferior quadrants in contralateral EG eyes. This shift indicates that significant connective tissue damage and/or remodeling is present in early glaucoma.
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