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J. Chen, G. Brent, S. Evans, F. Manns, J.–M. Parel, A. Ho; Finite Element Modelling the Influence of Capsule Property on the Accommodation of a Refilled Crystalline Lens . Invest. Ophthalmol. Vis. Sci. 2005;46(13):726.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Lens refilling technique is an emerging surgical option for restoring accommodation in presbyopes. However, the influence of many ocular parameters on this technique is not known. We modelled the influence of lens capsule modulus on accommodation. Methods: A 2–D, axisymmetric model was constructed using finite element package MSC Marc. The model consisted of 5809 elements. The capsular layer was modelled by modifying the properties of the surface elements. Lens content was modelled using 4–noded axisymmetric incompressible elements and the zonules by three 2–noded membrane elements attached symmetrically about the equator of the lens. The intersection of the three zonular elements was adopted as the ‘stretching point’ of the ciliary body. For the surface profiles we adopted the 5th–order polynomial model developed by Burd (2002). Capsule thickness profile was taken from the results of Fisher & Pettet (1972). The properties of the capsule and zonules were based on values from Krag et al (1996) and Fisher (1971). To test the influence of capsule stiffness on accommodation, five different capsule moduli were tested being 0.25×, 0.5×, 1×, 2×, and 4× (Krag et al, 1996) published mean values. For each capsule modulus, the lens model was stretched (disaccommodated) radially at the ciliary body ‘stretching point’ from its fully relaxed (accommodated) state to a total displacement of 0.5 mm over 30 equidistant increments. The anterior and posterior curvatures of the lens in the relaxed and stretched states were fitted with 6th–order even polynomials and the axial thickness change was computed. Results: There was a progressive decrease in the change of thickness from 0.54 mm to 0.30 mm as capsule modulus increased from 0.25× to 4× reference value suggesting that lower capsule modulus is associated with higher accommodative range. This is supported by the stretched surface profiles for the 0.25× (front=0.2.r6 –1.2.r4 –48.8.r2, back=–1.4.r6 +9.r4 +113.r2 in µm) and 4× (front=0.06.r6 +1.r4 –75.3.r2, back=–0.8.r6 +5.2.r4 +129.6.r2) where –2mm<r<2mm. Conclusions: The lens model predicts that accommodative range following lens refilling is greater with decreasing capsule modulus. This has implications with respect to the effect of ageing on performance with lens refilling.
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