Department of Optometry and Vision Sciences, University of Auckland, Building 502, Level 4, 85 Park Road, Grafton, Auckland, New Zealand.
Biomed Eng Online. 2012 Sep 19;11:69. doi: 10.1186/1475-925X-11-69.
It has been proposed that in the absence of a blood supply, the ocular lens operates an internal microcirculation system. This system delivers nutrients, removes waste products and maintains ionic homeostasis in the lens. The microcirculation is generated by spatial differences in membrane transport properties; and previously has been modelled by an equivalent electrical circuit and solved analytically. While effective, this approach did not fully account for all the anatomical and functional complexities of the lens. To encapsulate these complexities we have created a 3D finite element computer model of the lens.
Initially, we created an anatomically-correct representative mesh of the lens. We then implemented the Stokes and advective Nernst-Plank equations, in order to model the water and ion fluxes respectively. Next we complemented the model with experimentally-measured surface ionic concentrations as boundary conditions and solved it.
Our model calculated the standing ionic concentrations and electrical potential gradients in the lens. Furthermore, it generated vector maps of intra- and extracellular space ion and water fluxes that are proposed to circulate throughout the lens. These fields have only been measured on the surface of the lens and our calculations are the first 3D representation of their direction and magnitude in the lens.
Values for steady state standing fields for concentration and electrical potential plus ionic and fluid fluxes calculated by our model exhibited broad agreement with observed experimental values. Our model of lens function represents a platform to integrate new experimental data as they emerge and assist us to understand how the integrated structure and function of the lens contributes to the maintenance of its transparency.
有人提出，在没有血液供应的情况下，眼球晶状体内部运行着一个微循环系统。这个系统为晶状体输送营养物质、清除代谢废物并维持离子平衡。该微循环是由膜转运特性的空间差异产生的；此前，它已通过等效电路模型和解析方法进行了建模。虽然这种方法有效，但它并没有完全考虑到晶状体的所有解剖学和功能复杂性。为了包含这些复杂性，我们创建了一个晶状体的 3D 有限元计算机模型。
首先，我们创建了一个具有代表性的晶状体解剖结构网格。然后，我们实现了 Stokes 和对流 Nernst-Plank 方程，以分别模拟水和离子通量。接下来，我们用实验测量的表面离子浓度作为边界条件来补充模型，并对其进行了求解。
我们的模型计算出了晶状体中的离子浓度和静息电位梯度。此外，它生成了细胞内和细胞外空间离子和水通量的向量图，这些通量被认为在整个晶状体中循环。这些场仅在晶状体表面进行了测量，我们的计算结果首次给出了它们在晶状体内部的方向和大小的 3D 表示。
我们的模型计算出的稳态静息场值，包括浓度和电势能以及离子和流体通量，与观察到的实验值具有广泛的一致性。我们的晶状体功能模型代表了一个平台，可以整合新的实验数据，帮助我们了解晶状体的整体结构和功能如何有助于其透明度的维持。
