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J. R. Kuszak, G. Gray, R. Frey; Results From a Finite Element Model Analysis of the Accommodative Process Based on the Human Crystalline Lens Fiber Ultrastructure. Invest. Ophthalmol. Vis. Sci. 2007;48(13):988.
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To study the accommodative process utilizing detailed human crystalline lens fiber geometry and suture development with age in a comprehensive engineering finite element (FE) simulation and analysis.
An anatomically correct geometric model of the human crystalline lens has been constructed utilizing a custom software program based on Kuszak et al (2004). FE analysis was performed using the nonlinear finite element program LS Dyna. Lagrangian brick elements are used to create individual lens fibers which follow the opposite end-curvature and suture formation with age for the lens cortex and nucleus. A model of the zonule connection was stretched and the resulting lens capsule surface profile was analyzed to determine refractive power as a function of zonular forces.
The results shows that forces from the ciliary muscles acting on the equator of the lens capsule through the zonula, convert this radial force to predominately inward polar forces acting to compress the fiber mass. The geometry of the fibers and suture connections reduce the forces required to flatten the lens because the curved fibers can straighten as has been shown in correlative structure/function studies (Kuszak & Zoltoski, 2006). Results show that increasing the material modulus of elasticity is not required at all to account for lens hardening with age. Rather, a reduction in micro sliding as a result of compaction and/or increased friction due to fiber surface morphology changes, or other causes, may be solely responsible for accommodative amplitude loss.
A new and comprehensive anatomically based geometric FE model of the lens which takes into account the development of lens sutures with age produces accommodative amplitude results in agreement with Duane (1922), Glasser et al (1998, 2001 and 2006) and Burd (2002). The impact of fiber sliding is shown to be significant and may have implications for potential treatment of accommodative loss.
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