Abstract

We present a patient-specific finite element model of the human cornea that accounts for the presence of the epithelium. The thin anterior layer that protects the cornea from the external actions has a scant relevance from the mechanical point of view, and it has been neglected in most numerical models of the cornea, which assign to the entire cornea the mechanical properties of the stroma. Yet, modern corneal topographers capture the geometry of the epithelium, which can be naturally included into a patient-specific solid model of the cornea, treated as a multi-layer solid. For numerical applications, the presence of a thin layer on the anterior cornea requires a finer discretization and the definition of two constitutive models (including the corresponding properties) for stroma and epithelium. In this study, we want to assess the relevance of the inclusion of the epithelium in the model of the cornea, by analyzing the effects in terms of uncertainties of the mechanical properties, stress distribution across the thickness, and numerical discretization. We conclude that if the epithelium is modeled as stroma, the material properties should be reduced by 10%. While this choice represents a sufficiently good approximation for the simulation of in vivo mechanical tests, it might result into an under-estimation of the postoperative stress in the simulation of refractive surgery.

中文翻译：

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将上皮纳入人类角膜的数值模型中

摘要

我们提出了一个特定于患者的人类角膜有限元模型，该模型解释了上皮的存在。从机械角度来看，保护角膜免受外部作用的薄前层几乎没有相关性，并且在大多数角膜数值模型中都忽略了它，这些模型将基质的机械特性分配给整个角膜。然而，现代角膜地形图仪捕获了上皮的几何形状，可以将其自然地包含到患者特定的角膜实体模型中，并将其视为多层实体。对于数值应用，前角膜上存在薄层需要更精细的离散化以及基质和上皮的两个本构模型（包括相应的属性）的定义。在本研究中，我们希望通过分析机械性能的不确定性、厚度上的应力分布和数值离散化的影响，评估角膜模型中包含上皮的相关性。我们得出的结论是，如果将上皮建模为基质，则材料特性应降低 10%。虽然这种选择代表了体内机械测试模拟的足够好的近似值，但它可能会导致屈光手术模拟中术后应力的低估。