BACKGROUND It is well known that the biomechanical properties change after LASIK refractive surgery. One reason is the impact of flap creation on the residual stroma. The results have revealed that the change is closely related with the flap thickness in several studies. However, the quantitative relationships between the distributions of displacement and stress on the corneal surface and flap thickness have not been studied. The aim of the study was to quantify evaluate the biomechanical change caused by the LASIK flap. METHODS By building a finite element model of the cornea, the displacement, the stress and the strain on the corneal surface were analyzed. RESULTS The results showed that the corneal flap could obviously cause the deformation of the anterior corneal surface. For example, the displacement of the corneal vertex achieved 15 μm more than that without corneal flap, when the thickness of corneal flap was 120 μm thick. This displacement was enough to cause the change of aberrations in the human eyes. In the central part of the cornea, the stress on the anterior corneal surface increased with flap thickness. But the change in the stress on the posterior corneal surface was significantly less than that on the anterior surface. In addition, the stress in the central part of the anterior corneal surface increased significantly as the intra-ocular pressure (IOP) increase. Furthermore the increase of IOP had a clearly less effect on stress distribution at the edge of the cornea. Distributions of strain on the corneal surface were similar to those of stress. CONCLUSIONS The changes in the biomechanical properties of cornea after refractive surgery should not be ignored.

中文翻译：

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LASIK皮瓣厚度对角膜生物力学行为的影响：有限元分析。

背景技术众所周知，在LASIK屈光手术后，生物力学性质发生变化。原因之一是皮瓣产生对残留基质的影响。结果表明，在一些研究中，这种变化与皮瓣厚度密切相关。但是，尚未研究角膜表面位移和应力分布与皮瓣厚度之间的定量关系。这项研究的目的是量化评估由LASIK皮瓣引起的生物力学变化。方法通过建立角膜的有限元模型，分析角膜表面的位移，应力和应变。结果结果表明，角膜瓣明显引起角膜前表面的变形。例如，当角膜瓣的厚度为120μm时，角膜顶点的位移比没有角膜瓣的位移大15μm。这种位移足以引起人眼中像差的改变。在角膜的中央部分，角膜前表面的应力随着皮瓣厚度的增加而增加。但是，角膜后表面的应力变化明显小于前表面。此外，随着眼内压（IOP）的增加，角膜前表面中央部分的应力显着增加。此外，眼压的增加对角膜边缘应力分布的影响明显较小。角膜表面的应变分布与应力分布相似。