Han Shaofeng, He Changyan, Ma Ke, Yang Yang
School of Mechanical Engineering & Automation, Beihang University, 100191, Beijing, China.
Beijing Institute of Ophthalmology, Beijing TongRen Eye Center, Beijing TongRen Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Lab, 100730, Beijing, China.
Comput Methods Programs Biomed. 2021 May;203:106025. doi: 10.1016/j.cmpb.2021.106025. Epub 2021 Feb 28.
During capsulotomy, the force applied to the anterior capsule is a crucial parameter controlling capsule tears, that affects the clinical performance. This study aims to investigate the tear force in capsulotomy and analyze the effects of different tearing conditions on the tear force.
A three-dimensional model of the human lens was constructed based on published clinical data using the finite element (FE) method. The lens model consisted of four layers: the anterior and posterior lens capsule, the cortex, and the nucleus. Distortion energy failure criterion combined with the bilinear interface law was used to express the crack propagation process at the edge of the anterior lens capsule. At the clamping position, a local coordinate system was established to parameterize the capsule tearing. The simulation results were then validated by conducting a capsulorhexis experiment using isolated porcine eyes with force-sensing forceps.
The simulation results showed a good agreement with the experimental data of two porcine specimens (No. 6 and 9) during a stable tearing process (p-values = 0.76 and 0.10). The mean force differences between the experimental data and the simulation were 3.10 ± 2.24 mN and 2.14 ± 1.73 mN, respectively. The tear direction with a minimum mean tear force was at θ = 0° and θ = 30°. The tear velocity was not significantly different to the variation in the tear force. However, an appropriate capsulorhexis diameter was found to contribute to the reduction of tear force.
The outcome of this paper demonstrates that our FE model could be used in modeling lens capsule tearing and the theoretical study of tear mechanism.
在晶状体囊切开术中，施加于前囊膜的力是控制囊膜撕裂的关键参数，会影响临床效果。本研究旨在探究囊切开术中的撕裂力，并分析不同撕裂条件对撕裂力的影响。
基于已发表的临床数据，采用有限元（FE）方法构建人晶状体的三维模型。晶状体模型由四层组成：晶状体前囊膜和后囊膜、皮质和核。采用畸变能失效准则结合双线性界面定律来表达晶状体前囊膜边缘的裂纹扩展过程。在夹持位置建立局部坐标系，对囊膜撕裂进行参数化。然后使用带有力传感镊子的离体猪眼进行撕囊实验，对模拟结果进行验证。
在稳定撕裂过程中，模拟结果与两个猪标本（6号和9号）的实验数据显示出良好的一致性（p值分别为0.76和0.10）。实验数据与模拟结果的平均力差分别为3.10±2.24 mN和2.14±1.73 mN。平均撕裂力最小的撕裂方向为θ = 0°和θ = 30°。撕裂速度与撕裂力的变化无显著差异。然而，发现合适的撕囊直径有助于降低撕裂力。
本文结果表明，我们的有限元模型可用于模拟晶状体囊膜撕裂及撕裂机制的理论研究。
