Pant Anup D, Kagemann Larry, Schuman Joel S, Sigal Ian A, Amini Rouzbeh
Department of Biomedical Engineering, The University of Akron, Akron, OH, USA.
Lead Reviewer and Biomedical Engineer, Division of Ophthalmic and ENT Devices, Off ice of Device Evaluation, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD, USA.
J Model Ophthalmol. 2017;1(3):100-111.
Previous studies have shown that the trabecular meshwork (TM) is mechanically stiffer in glaucomatous eyes as compared to normal eyes. It is believed that elevated TM stiffness increases resistance to the aqueous humor outflow, producing increased intraocular pressure (IOP). It would be advantageous to measure TM mechanical properties , as these properties are believed to play an important role in the pathophysiology of glaucoma and could be useful for identifying potential risk factors. The purpose of this study was to develop a method to estimate TM mechanical properties using clinically available exams and computer simulations.
Inverse finite element simulation.
A finite element model of the TM was constructed from optical coherence tomography (OCT) images of a healthy volunteer before and during IOP elevation. An axisymmetric model of the TM was then constructed. Images of the TM at a baseline IOP level of 11, and elevated level of 23 mmHg were treated as the undeformed and deformed configurations, respectively. An inverse modeling technique was subsequently used to estimate the TM shear modulus (). An optimization technique was used to find the shear modulus that minimized the difference between Schlemm's canal area in the images and simulations.
Upon completion of inverse finite element modeling, the simulated area of the Schlemm's canal changed from 8,889 µm to 2,088 µm, similar to the experimentally measured areal change of the canal (from 8,889 µm to 2,100 µm). The calculated value of shear modulus was found to be 1.93 kPa, (implying an approximate Young's modulus of 5.75 kPa), which is consistent with previous measurements.
The combined imaging and computational simulation technique provides a unique approach to calculate the mechanical properties of the TM without any surgical intervention. Quantification of such mechanical properties will help us examine the mechanistic role of TM biomechanics in the regulation of IOP in healthy and glaucomatous eyes.
以往研究表明，与正常眼相比，青光眼患者的小梁网（TM）机械硬度更高。据信，小梁网硬度升高会增加房水流出阻力，导致眼压（IOP）升高。测量小梁网的机械性能将具有重要意义，因为这些性能被认为在青光眼的病理生理学中起重要作用，并且可能有助于识别潜在风险因素。本研究的目的是开发一种利用临床可用检查和计算机模拟来估计小梁网机械性能的方法。
逆向有限元模拟。
根据一名健康志愿者在眼压升高前后的光学相干断层扫描（OCT）图像构建小梁网的有限元模型。然后构建小梁网的轴对称模型。将眼压基线水平为11mmHg和升高水平为23mmHg时的小梁网图像分别视为未变形和变形构型。随后使用逆向建模技术估计小梁网剪切模量（）。采用优化技术找到使图像和模拟中小梁网区域差异最小的剪切模量。
逆向有限元建模完成后，小梁网模拟区域从8889μm²变为2088μm²，与实验测量的小梁网区域变化（从8889μm²变为2100μm²）相似。计算得到的剪切模量值为1.93kPa（意味着近似杨氏模量为5.75kPa），这与先前的测量结果一致。
联合成像和计算模拟技术提供了一种无需任何手术干预即可计算小梁网机械性能的独特方法。对这些机械性能进行量化将有助于我们研究小梁网生物力学在健康眼和青光眼眼中眼压调节中的作用机制。
