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H. Subramaniam, J. R. Kuszak, G. P. Gray, R. W. Frey; Finite Element Analysis of the Accommodation Process in the Whole Globe. Invest. Ophthalmol. Vis. Sci. 2007;48(13):987.
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To understand the mechanisms involved in accommodation using a finite element (FE) model which incorporates the key anatomical structures known to play a role in the accommodation process: crystalline lens, lens capsule, zonules, ciliary muscle, and choroid and elements contained within the globe including the cornea, aqueous and vitreous.
A 3-D model of the whole globe has been constructed and FE analysis was performed using the nonlinear finite element program LS Dyna. Lagrangian membrane elements are used for the cornea, sclera, lens capsule, and choroid, Lagrangian brick elements for the lens cortex and nucleus, and ciliary muscle, and Eulerian brick elements for the aqueous and vitreous. The lens was modeled using the fiber ultrastructure details of suture geometry based on Kuszak et al (2004). The ciliary muscle was stretched and the resulting lens capsule surface profile was analyzed to determine refractive power as a function of ciliary muscle displacement within the aqueous/vitreous environment.
The results shows how multiple attributes of the human accommodation apparatus act together to result in crystalline lens central curvature flattening under zonule tension according to Helmholtz, including agreement with accommodation dynamics (several hundred milliseconds) found by Glasser et al (1998, 2001 and 2006) and others. The results also show how the effects of aging and geometrical changes play a role in accommodation decline over time. The results show smaller zonular force compared to Burd (2002) model for equivalent equatorial displacement, while amplitudes of accommodation (9.7 Diopter for the 29 year old and 3.5 Diopter for the 45 year old) agree with Duane (1922).
FE Modeling has shown that the human accommodation system is unique from a mechanical engineering viewpoint and considerations of many anatomical elements are required to properly understand the complex mechanism of accommodation and accommodative loss.
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