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Yik Tung Tracy Ling, Arina Korneva, Harry A Quigley, Thao D. Nguyen; Computational Model of the Stress and Deformation Response of the Mouse Astrocytic Lamina to Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1653.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a computational biomechanical model of the mouse astrocytic lamina (AL) and investigate the effect of the AL network structure on the local stress and strain response to increased intraocular pressure (IOP).
An unmyelinated optic nerve section of a 6-month old GFP-GLT1 mouse was immunolabeled for GFAP and stained for actin and nuclei(Ling et al. 2020, Fig 1a). The non-GFAP and non-actin regions in the acquired confocal image were segmented as axonal compartments(ACs). A finite element model(FEM) was created using the GFAP, actin and AC labels in Gibbon Toolbox(Fig 1b). Nodal displacements were applied to the side surface of the AL using average of measured boundary displacements from 7 mouse eye explants that were inflated from 10 to 30 mmHg(Korneva et al. 2020). A pressure of 20 mmHg was applied on the anterior surface of the model to simulate the inflation test(Fig 1c). The GFAP, actin and ACs were assumed to be incompressible Neo-Hookean materials with shear moduli of 2.4MPa(Guzman et al. 2006), 21.2MPa(Janmey et al. 1991) and 1.9kPa(Budday et al. 2015), respectively. Bulk modulus for each material was assumed to be 100 times larger than the shear modulus. The effect of axonal area on strains simulated in FEBio was analyzed using a linear regression model in MATLAB.
Preliminary results showed that the average nasal-temporal strain(Exx=0.033, Fig 2a) in the AL was higher than the inferior-superior strain(Eyy=0.026), while the anterior-posterior strain was compressive(Ezz=-0.021). This agreed with the inflation test results. The maximum principal strain(Emax) was larger in the ACs(0.03±0.10) compared to that experienced by GFAP and actin structures in the astrocyte processes(0.01±0.02 and 0.02±0.01, p<0.01, Fig 2b&d). However, the maximum principal stress(σmax) was lower in the ACs (0.0058 MPa) when compared to that in GFAP(0.77 MPa) and actin(1.64 MPa, p<0.01, Fig 2c). Greater tensile strains Exx and Eyy and greater compressive strains Ezz were obtained for larger ACs(Fig 2e&f, p<0.05). The model will be applied to examine the effects of fiber tortuosity and aspect ratio on the stress and strain response in the astrocyte processes and AC.
A specimen-specific FEM of the AL suggested that larger ACs experienced higher strain magnitudes. Variations in AL network structure may be related to the susceptibility of axonal damage in glaucoma.
This is a 2021 ARVO Annual Meeting abstract.
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