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Richard Regueiro, Louis Foucard, Franck Vernerey, Christopher Bay; Large deformation indentation of porcine ocular lenses: experiments and computational modeling. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1081.
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© ARVO (1962-2015); The Authors (2016-present)
Mechanical characterization and modeling of the human lens can lead to increased understanding of trauma suffered (e.g., by Intra-Ocular Foreign Body (IOFB) penetration) and effects of surgical procedures on the lens, thus possibly leading to better surgical treatments and vision correction methods.
Fresh 2+ year-old porcine eyes obtained <1 day post-mortem are dissected to extract the lens, which is then immersed for testing in a cup full of Balanced Salt Solution (BSS) warmed to 39.2°C (pig body temperature) to attempt to reduce the non-physiological effects of testing in-vitro. A puncture tip (6 different geometries) indents the lens (anteriorly and posteriorly) along its anterior-posterior axis at a displacement rate of 0.3 mm/s to 80% nominal strain. The capsule fails, either by puncture at the tip or by bulging rupture along the equatorial region. Force is measured and digital videos are taken of the indented lenses. Computational modeling using a coupled Lagrangian-Eulerian approach simulates the internal fiber cells as an isotropic viscous fluid (for now, see image), and the lens capsule as a hyperelastic impermeable membrane undergoing large deformation (no failure at the moment). The constitutive behavior of the capsule is derived using a multi-scale homogenization analysis of the deformation of a two-dimensional lattice approximation of the underlying type IV collagen meshwork structure. Axisymmetric conditions are assumed in the simulations up to puncture.
The experimentally-measured and computationally-simulated force-displacement curves for extracted lenses, and membrane-fluid interaction of the capsule and internal substance, are matched up to large deformation before puncture.
Indentation loading is meant to mimic perforation by an IOFB. Currently, the experimental method is limited in that it ignores relaxation and tension in the zonules attached to the equatorial region of the lens capsule, and in turn the attachment of the zonules to the ciliary body. The method, however, successfully represents the puncture response of the whole lens. The coupled Eulerian-Lagrangian computational method allows for the first time the simulation of large indentation of the lens, accounting for capsule-substance interaction.
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