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J Crawford C Downs, Christopher A Girkin, Seyed Mohammadali Rahmati, Rafael G Grytz, Alireza Karimi; Microstructural Finite Element Modeling of the Entire Lamina Cribrosa in the Human Optic Nerve Head. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1655.
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© ARVO (1962-2015); The Authors (2016-present)
The microstructure of the lamina cribrosa (LC), including the size, volume fraction, and orientation of the LC beams likely play a crucial role in protecting the retinal ganglion cell axons passing through the scleral canal. Prior computational models have been limited to multiscale approaches, in which a small chunk of the LC microstructure is subjected to displacement boundary conditions predicted from a parent mesoscale model. This regional approach cannot calculate the stresses and strains across the entire LC, and is unable to accurately represent the relatively compliant neural tissues (NT).
A finite element (FE) model of posterior pole of the eye was developed, including the LC microstructure that is constructed directly from the binary images of the LC microstructure (Figure). Models of three human donor eye were used to estimate the stresses and strains in the LC and NT under acute IOP elevation, and compared with identical models in which the LC was represented as a single material with either mapped connective tissue volume fraction (CTVF) and anisotropic properties based on local LC beam direction, or homogeneous isotropic neo-Hookean properties. The models were subjected to an IOP elevation to 45 mmHg after pre-stressing from 0 to 10 mmHg, and solved in CalculiX. ONH and LC displacements were matched across the three modeling approaches within each eye, and stresses and strains were compared for the LC and NT combined (continuum material and microstructural), and the LC and NT separately.
The regional volumetric average von Mises stress, and 1st, 2nd, and 3rd principal stresses and strains showed that the microstructural model with neo-Hookean properties yielded similar results to our prior approach using an LC continuum representation with mapped CTVF/anisotropy, but the microstructural modeling approach allows analysis of the stresses and strains in the LC and NT separately. In the microstructural models, the LC beams carried most of the IOP load but exhibited less strain, while the encapsulated NT exhibited lower stresses and much higher strains. Strain levels matched prior experimental studies.
Microstructural modeling will provide greater insight into the biomechanical factors driving damage to the axons (NT) and connective tissue remodeling of the LC that occur in glaucoma.
This is a 2021 ARVO Annual Meeting abstract.
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