Elastic Properties of Human Lens Zonules as a Function of Age in Presbyopes

Venetsanos

et al. 2017

Sci Rep

The lens provides refractive power to the eye and is capable of altering ocular focus in response to visual demand. This capacity diminishes with age. Current biomedical technologies, which seek to design an implant lens capable of replicating the function of the biological lens, are unable as yet to provide such an implant with the requisite optical quality or ability to change the focussing power of the eye. This is because the mechanism of altering focus, termed accommodation, is not fully understood and seemingly conflicting theories require experimental support which is difficult to obtain from the living eye. This investigation presents finite element models of the eye lens based on data from human lenses aged 16 and 35 years that consider the influence of various modelling parameters, including material properties, a wide range of angles of force application and capsular thickness. Results from axisymmetric models show that the anterior and posterior zonules may have a greater impact on shape change than the equatorial zonule and that choice of capsular thickness values can influence the results from modelled simulations.

Section: Methodsmentioning

confidence: 96%

The importance of parameter choice in modelling dynamics of the eye lens

Venetsanos

et al. 2017

Sci Rep

Invest. Ophthalmol. Vis. Sci.

“…10 During accommodation, this tension is released via ciliary muscle contraction, allowing the lens to elastically recoil to a rounder shape. The ciliary muscle remains active into old age [11][12][13][14] and the mechanical properties of zonules are independent of age, 15 implying that the human lens capsule may experience cyclic tension even after the onset of presbyopia. In the context of presbyopia, younger lenses exhibit a large magnitude in focal length changes during stretching, while lenses above the age of 60 showed no changes in focal length with stretching, such that the eye is only able to focus on distant objects.…”

mentioning

confidence: 99%

Lens Stretching Modulates Lens Epithelial Cell Proliferation via YAP Regulation

Kumar

Chandler

Plageman

et al. 2019

PURPOSE. The continuous growth of the lens throughout life may contribute to the onset of age-related conditions in the lens (i.e., presbyopia and cataract). Volumetric growth is the result of continuous proliferation of lens epithelial cells (LECs). The driving factors controlling LEC proliferation are not well understood. This study tested the hypothesis that mechanical stretching modulates LEC proliferation. METHODS. Biomechanical regulation of LEC proliferation was investigated by culturing whole porcine lenses and connective tissues ex vivo under varying physiologically relevant stretching conditions using a bespoke lens stretching device. Additionally, some lenses were treated with a YAP function inhibitor to determine the Hippo signaling pathway's role in regulating lens growth. Resulting changes in LEC labeling index were analyzed using EdU incorporation and flow cytometry for each lens. RESULTS. LEC proliferation was found to be modulated by mechanical strain. Increasing both the magnitude of static stretching and the stretching frequency in cyclic stretching resulted in a proportional increase in the labeling indices of the LECs. Additionally, treatment with the YAP function inhibitor effectively eliminated this relationship. CONCLUSIONS. These data demonstrate that LEC proliferation is regulated in part, by the mechanotransduction of stresses induced in the lens capsule and that YAP plays an important role in mechanosensing. These results have important implications for understanding lens growth and morphogenesis. The model may also be used to identify and evaluate targets for modulating lens growth.

“…Poisson's ratio of 0.49 was used for the lens [22] and 0.47 for the capsule and zonular fibres [11,27]. Young's moduli of the lens capsule [11] and zonular fibres [28,29] are also given in Table 2. The lens nucleus and cortex were meshed using 8-node axisymmetric elements PLANE 183 in ANSYS mechanical APDL.…”

Section: Methodsmentioning

confidence: 99%

Contributions of shape and stiffness to accommodative loss in the ageing human lens: a finite element model assessment

et al. 2019

Ageing changes to the various components of the accommodative system of the eye lens contribute to the loss of focusing power. The relative contributions of each ageing component, however, are not well defined. This study investigates the contribution of geometric parameters and material properties on accommodation simulated using models based on human lenses aged 16, 35 and 48 years. Each model was tested using two different sets of material properties and a range of zonular fibre angles and compared to results from in vivo measurements. The geometries and material parameters of older and younger lens models were interchanged to investigate the role of shape and material on accommodative capacity. Results indicate that geometry has the greater role in accommodation.