# Accurate finite element analysis of an intraocular lens in a postcatarctous capsular bag during accommodation

Souéla Toumi, C. Cavinato, Amélie Lurton, Fabien Gayic, Fannie Castignoles, Philippe Sourdille, Denis Delage, Franck Jourdan

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## To cite this version:

Souéla Toumi, C. Cavinato, Amélie Lurton, Fabien Gayic, Fannie Castignoles, et al.. Accurate finite element analysis of an intraocular lens in a postcatarctous capsular bag during accommodation. Multidisciplinary Biomechanics Journal, 2025, 50th congress of the.., 10.46298/mbj.16246. hal-05191801v2

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Submitted on 23 Oct 2025

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# Accurate Finite Element Analysis of an Intraocular Lens in a Postcatarctous Capsular Bag During Accommodation

Souéla Toumi<sup>a*</sup>, Cristina Cavinato<sup>a</sup>, Amélie Lurton<sup>b</sup>, Fabien Gayic<sup>b</sup>, Fannie Castignoles<sup>b</sup>, Philippe Sourdille<sup>c</sup>, Denis Delage<sup>b</sup>, Franck Jourdan<sup>a</sup>

<sup>a</sup> LMGC, Université de Montpellier, CNRS, Montpellier, France

<sup>b</sup> Cristalens Industrie, Lannion, France

<sup>c</sup> Consultant for Cristalens Industrie

Received date: 06/04/2025

Accepted date: 27/06/2025

Publication date: 27/10/2025

**Keywords:** accommodation, numerical model, finite element, intraocular lenses

© 2025 The Authors
Licence CC-BY 4.0
Published by Société de Biomécanique

## 1. Introduction

Cataract is a pathological condition characterized by lens opacification, leading to reduced visual quality. The primary treatment involves the surgical replacement of the native lens (composed of the cortex and nucleus) with an intraocular lens (IOL) implanted in the capsular bag. The most effective IOLs provide vision at multiple distances by modulating light into multiple focal points. However, this process induces photic effects due to circles of confusion from defocused objects on the retina.

A more effective solution is an IOL capable of adjusting its focal point in response to visual demands through axial movement of its optical component via physiological accommodation.

Our final aim is to restore accommodation by designing a novel Accommodating IOL (AIOL). The objective of this study is to develop an accurate numerical model to predict the mechanical behavior of AIOLs within the capsular bag during accommodation.

## 2. Methods

The model (Fig. 1a) was created using an average on in vivo geometric measurements (Dubbelman, Van der Heijde, & Weeber, 2005; Wagner, Zrenner, & Strasser, 2019). We decided to model the iris in this simulation to verify that it does not hinder the movement of the optics during accommodation.

All components of the model exhibit linear isotropic elastic behavior, except for the capsular bag, which has a hyper elastic behavior (Krag & Andreassen, 2003). The IOL is made of CBK1.8 polymer (Cristalens Industrie), characterized by uniaxial tensile tests and inflation tests conducted during our investigation. All mechanical properties were defined based on the average values of the experimental data.

The iris is bonded to the capsular bag with frictionless contact, while the IOL is bonded to the capsular bag with a friction coefficient of 0.1. The ciliary body and ciliary muscle, the capsular bag and cortex, and the cortex and nucleus are defined as fully bonded.

According to Helmholtz's theory, accommodation relies on zonular tension to modulate the lens shape. For far vision, the zonules apply tension to the capsular bag, flattening the lens. For near vision, contraction of the ciliary muscle releases this tension, allowing the lens to curve and increase its refractive power.

The ciliary muscle contraction is simulated as a displacement of its internal surface (the one in contact with the ciliary body), calculated from in vivo measurements of the ciliary muscle thickness at near and far vision (Wagner, Zrenner, & Strasser, 2019).

The simulations were performed using the ARTIS SYMBIOSE IOL (® Cristalens Industrie) using ANSYS workbench 2024 in a quarter of the model with a symmetric assumption.
## 3. Results and discussion

First, simulations were conducted to validate the numerical model. Then we evaluated the positioning and the response of the IOL under physiological conditions.

### 3.2 Model evaluation

To be confident with the model, we conducted two steps based on comparisons with in vivo data of crystalline lens deformation during accommodation.

In Simulation A, the lens was deformed by applying a 40 mN zonular load to assess the adequacy of the selected geometry and mechanical properties for both the lens and capsular bag. In Simulation B, the lens deformation was driven by the full accommodative process, allowing us to evaluate the accuracy of the ciliary muscle contraction modeling.

The results obtained for simulations A and B (Table 1) show good agreement with experimental in vivo data, supporting the consistency of our accommodation model with physiological accommodation.

### 3.2 Behavior of the IOL at accommodative rest

First, we validated the mechanical behavior of the IOL, comparing the axial displacement of the IOL optic in a radial clamping device measured experimentally using optical coherence imaging with a similar simulation. The measured displacement, 1.49 mm, and the calculated displacement, 1.42 mm, are very close.

Once the numerical model of the capsular bag and the mechanical behavior of the implant were verified, the crystalline lens was replaced with an IOL. We can now predict the axial displacement of the optic within the capsular bag (0.2 mm in this case, Fig. 1b) at the rest state. For a more robust validation, it would be relevant to compare the positioning of the IOL in a capsular bag with post-operative in vivo images.

## 4. Conclusions

The numerical model accurately predicts the mechanical behavior of IOLs within the capsular bag. It not only provides an essential foundation for the development of a new IOL but also can be used to prevent refractive errors and instabilities in existing IOLs. The next step is to simulate the behavior of the IOL within the capsular bag during accommodation.

<figure><img src="image_3.png" /><figcaption>**Figure 1.** (a) Geometry of the numerical model of accommodation, (b) Simulation of the ARTIS SYMBIOSE IOL positioned in the capsular bag, with the undeformed position outlining in black.</figcaption></figure>

<table><caption>**Table 1.** Comparison between the dimensional variations (diameter: Δd, thickness: Δt) of the crystalline lens measured in vivo and numerically calculated.</caption><thead><tr><th></th><th>In vivo</th><th>A</th><th>B</th></tr></thead><tbody><tr><td>Δd (mm)</td><td>0,23</td><td>0,27</td><td>0,21</td></tr><tr><td>Δt (mm)</td><td>0,26</td><td>0,28</td><td>0,30</td></tr></tbody></table>

## Conflict of Interest Statement

None.

## Funding

This work was funded by Cristalens Industrie.

## References

Dubbelman, M., Van der Heijde, G. L., & Weeber, H. A. (2005). Change in shape of the aging human crystalline lens with accommodation. *Vision*
*Research, 45*, 117–132. https://doi.org/10.1016/j.visres.2004.07.032

Hermans, E. A., Dubbelman, M., van der Heijde, G. L., & Heethaar, R.M. (2006). Estimating the external force acting on the human eye lens during accommodation by finite element modelling. *Vision Research*, *46*, 3642–3650. https://doi.org/10.1016/j.visres.2006.04.012

Krag, S., & Andreassen, T. T. (2003). Mechanical properties of the human lens capsule. *Progress in Retinal and Eye Research*, *22*, 749–767. https://doi.org/10.1016/S1350-9462(03)00063-6

Wagner, S., Zrenner, E., & Strasser, T. (2019). Emmetropes and myopes differ little in their accommodation dynamics but strongly in their ciliary muscle morphology. *Vision Research*, *163*, 42–51. https://doi.org/10.1016/j.visres.2019.08.002