Ramirez-Garcia Manuel A, Sloan Stephen R, Nidenberg Bennett, Khalifa Yousuf M, Buckley Mark R
a Department of Biomedical Engineering , University of Rochester , Rochester , NY , USA.
b Department of Ophthalmology , Emory University , Atlanta , GA , USA.
Curr Eye Res. 2018 May;43(5):595-604. doi: 10.1080/02713683.2017.1411951. Epub 2017 Dec 28.
Purpose/Aim: Despite their importance in accurate mechanical modeling of the cornea, the depth-dependent material properties of the cornea have only been partially elucidated. In this work, we characterized the depth-dependent out-of-plane Young's modulus of the central and peripheral human cornea with high spatial resolution.
Central and peripheral corneal buttons from human donors were subjected to unconfined axial compression followed by stress relaxation for 30 min. Sequences of fluorescent micrographs of full-thickness corneal buttons were acquired throughout the experiment to enable tracking of fluorescently labeled stromal keratocyte nuclei and measurements of depth-dependent infinitesimal strains. The nominal (gross) out-of-plane Young's modulus and drained Poisson's ratio for each whole specimen was computed from the equilibrium stress and overall tissue deformation. The depth-dependent (local) out-of-plane Young's modulus was computed from the equilibrium stress and local tissue strain based on an anisotropic model (transverse isotropy).
The out-of-plane Young's modulus of the cornea exhibited a strong dependence on in-plane location (peripheral versus central cornea), but not depth. The depth-dependent out-of-plane Young's modulus of central and peripheral specimens ranged between 72.4-102.4 kPa and 38.3-58.9 kPa. The nominal out-of-plane Young's modulus was 87 ± 41.51 kPa and 39.9 ± 15.28 kPa in the central and peripheral cornea, while the drained Poisson's ratio was 0.05 ± 0.02 and 0.07 ± 0.04.
The out-of-plane Young's modulus of the cornea is mostly independent of depth, but not in-plane location (i.e. central vs. peripheral). These results may help inform more accurate finite element computer models of the cornea.
目的/目标：尽管角膜深度依赖性材料特性在角膜精确力学建模中很重要，但目前仅得到部分阐明。在本研究中，我们以高空间分辨率表征了人眼角膜中央和周边区域的深度依赖性面外杨氏模量。
取自人类供体的中央和周边角膜纽扣组织先进行无侧限轴向压缩，然后进行30分钟的应力松弛。在整个实验过程中获取全层角膜纽扣组织的荧光显微图像序列，以便追踪荧光标记的基质角膜细胞细胞核，并测量深度依赖性微小应变。根据平衡应力和整体组织变形计算每个完整标本的名义（总）面外杨氏模量和排水泊松比。基于各向异性模型（横向各向同性），根据平衡应力和局部组织应变计算深度依赖性（局部）面外杨氏模量。
角膜的面外杨氏模量强烈依赖于平面内位置（周边角膜与中央角膜），但与深度无关。中央和周边标本的深度依赖性面外杨氏模量范围分别为72.4 - 102.4 kPa和38.3 - 58.9 kPa。中央和周边角膜的名义面外杨氏模量分别为87±41.51 kPa和39.9±15.28 kPa，而排水泊松比分别为0.05±0.02和0.07±0.04。
角膜的面外杨氏模量大多与深度无关，但与平面内位置有关（即中央与周边）。这些结果可能有助于建立更精确的角膜有限元计算机模型。
