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Benjamin J. Coldrick, J G. Swadener, Leon N. Davies; Using Finite Element Analysis To Measure The Impact Of Different Crystalline Lens Internal Structure Models During Accommodation. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1348. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the impact of different internal structure models on crystalline lens deformation using Finite Element Analysis (FEA) to provide a more accurate FEA model of the accommodation process.
Four models of the internal lens structure were tested. All were of a de-capsulated, fully accommodated, 30 year old crystalline lens, segmented into the appropriate number of shells. Model A (2 shells) included a nucleus and cortex, as commonly used in previous FEA studies. Model B (10 shells) was based on the stiffness gradient used by Weeber and Van de Heijde (2007). Model C (5 shells) was based on the work of Taylor et al (2006). Model D (4 shells) was based on the work of Dubbelman et al (2003).These were modelled using ANSYS (version 12.1) as being linear elastic and isotropic. The mechanical properties for each segment were taken from the stiffness values for a 30 year old lens as measured by Weeber et al (2007). Each model was spun around its axis at 1000rpm, partially replicating the deformations encountered during disaccommodation. The deformations were compared in terms of optical power, axial thickness, volume and surface area.A further four models (E-H) were created using the same lens forms to allow a comparison between the theoretical data and previously published ex vivo results (Burd et al (2011) spinning lens test). These models were digitally mounted onto a support before being spun.
Models A-D showed relatively minor differences in lens deformation. The maximum power change ranged from 13.8D (C and D) to 14.7D (A). The maximum axial thickness changes ranged from 0.71mm (C and D) to 0.78mm (B). The maximum volume change ranged from 0.77 (A) to 1.04mm3 (D) and the maximum surface area change ranged from 9.71 (D) to 10.71 mm2 (A). For models E-H, the power and thickness changes were closer to those measured by Burd et al.
Altering the internal structure of the crystalline lens FEA model has little impact on axial thickness change, but a larger impact on power change with accommodation. Further work is needed to clarify the relationships between thickness, volume and curvature changes in the different models.
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