Modeling fluid mixing within the crystalline lens during accommodation

Abstract Purpose: Historically, cataract and presbyopia are treated as separate entities. However, it has recently been hypothesized that as the ageing lens looses its ability to change shape, this reduces the mixing and transport of nutrients and antioxidants within the lens that normally occurs as the young, flexible lens alters its shape during accommodation. Such a loss of antioxidant mixing may render the lens more susceptible to cataract formation. Methods: We have developed a 3D cubic Hermite finite element model of the human lens to investigate the effect of increasing lens stiffness on fluid movement. Data obtained from previous studies are used to construct an anatomically accurate model. A spherical polar coordinate system is used to provide an accurate physical representation and as a framework to examine mechanics. Polynomial functions are used to define the lens surfaces. Lens capsule thickness and material properties of lens tissue are taken from the literature. Tension is applied via zonules to simulate accommodation. Results: Preliminary results verify that the change in shape of the lens surfaces (and the change in optical power) associated with displacement of the lens equator are similar to results from other published models and fall within the physiological range (i.e. using parameters for 30 y.o. lens, approx 25 dioptres per mm change in equatorial radius). We are currently investigating the fluid movements associated with these changes. Conclusions: Our lens model provides a basis for investigating fluid mixing in the young lens during simulated accommodation and also the reduction of fluid movement in stiffer, older lenses.