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J. C. Downs, M. D. Roberts, J. Grimm, C. F. Burgoyne, R. T. Hart; Stress and Strain in the Lamina Cribrosa Microstructure of the Monkey Eye. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6393.
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© ARVO (1962-2015); The Authors (2016-present)
To estimate IOP-related stress and strain in the lamina cribrosa microstructure of monkey eyes using finite element (FE) analysis, and to compare those results to values obtained from continuum-based models of the lamina as a solid, homogenized structure in the same eyes.
The optic nerve head (ONH) from one normal eye in each of 3 monkeys perfusion-fixed with IOP set to 10 mmHg were 3D reconstructed at 1.5 µm/voxel [IOVS 50(1):224-234, 2009]. 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 mmHg and the resultant displacement, stress and strain were calculated [Roberts et al. IOVS ePub ahead of print, 2009]. The 3D-segmented laminar microstructure within 4 continuum elements from the mid-periphery of each ONH model was surfaced, smoothed and converted into FE models of the laminar microstructure in that region [Downs et al. IEEE Conf Proc EMBS, in press, 2009]. 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. Resultant maximum principal (tensile) strain and von Mises stress were volume averaged for both the parent continuum elements and their laminar microstructure FE models for comparison.
For an IOP increase from 10 to 45 mmHg, mean laminar Von Mises stress and tensile strain were an average of 1527% and 68% higher in the laminar microstructure models than in their respective parent continuum elements, respectively. These results held for each of the 12 continuum model-to-microstructure model comparisons.
These results suggest that while solid, homogenized continuum models of the lamina cribrosa work well for generating regional, macro-scale distribution patterns of IOP-related stress and strain, they are likely to substantially underestimate the actual stress and strain in the laminar microstructure.
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