Karimi Alireza, Razaghi Reza, Kelley Mary J, Acott Ted S, Gong Haiyan
Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97208, USA.
Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97208, USA.
Bioengineering (Basel). 2023 Sep 4;10(9):1038. doi: 10.3390/bioengineering10091038.
More than ~70% of the aqueous humor exits the eye through the conventional aqueous outflow pathway that is comprised of the trabecular meshwork (TM), juxtacanalicular tissue (JCT), the inner wall endothelium of Schlemm's canal (SC). The flow resistance in the JCT and SC inner wall basement membrane is thought to play an important role in the regulation of the intraocular pressure (IOP) in the eye, but current imaging techniques do not provide enough information about the mechanics of these tissues or the aqueous humor in this area.
A normal human eye was perfusion-fixed and a radial wedge of the TM tissue from a high-flow region was dissected. The tissues were then sliced and imaged using serial block-face scanning electron microscopy. Slices from these images were selected and segmented to create a 3D finite element model of the JCT and SC cells with an inner wall basement membrane. The aqueous humor was used to replace the intertrabecular spaces, pores, and giant vacuoles, and fluid-structure interaction was employed to couple the motion of the tissues with the aqueous humor.
Higher tensile stresses (0.8-kPa) and strains (25%) were observed in the basement membrane beneath giant vacuoles with open pores. The volumetric average wall shear stress was higher in SC than in JCT/SC. As the aqueous humor approached the inner wall basement membrane of SC, the velocity of the flow decreased, resulting in the formation of small eddies immediately after the flow left the inner wall.
Improved modeling of SC and JCT can enhance our understanding of outflow resistance and funneling. Serial block-face scanning electron microscopy with fluid-structure interaction can achieve this, and the observed micro-segmental flow patterns in ex vivo perfused human eyes suggest a hypothetical mechanism.
超过70%的房水通过由小梁网（TM）、邻管组织（JCT）、施莱姆管（SC）内壁内皮组成的传统房水流出途径离开眼睛。JCT和SC内壁基底膜中的流动阻力被认为在眼睛眼压（IOP）调节中起重要作用，但目前的成像技术无法提供足够关于这些组织或该区域房水力学的信息。
对一只正常人类眼睛进行灌注固定，从高流量区域切下TM组织的径向楔形块。然后将组织切片并使用连续块面扫描电子显微镜成像。从这些图像中选择切片并进行分割，以创建具有内壁基底膜的JCT和SC细胞的三维有限元模型。用房水代替小梁间隙、孔隙和巨大液泡，并采用流固耦合将组织运动与房水耦合。
在具有开放孔隙的巨大液泡下方的基底膜中观察到更高的拉应力（0.8 kPa）和应变（25%）。SC中的体积平均壁面剪应力高于JCT/SC。当房水接近SC的内壁基底膜时，流速降低，导致水流离开内壁后立即形成小涡流。
改进的SC和JCT建模可以增强我们对流出阻力和漏斗效应的理解。具有流固耦合的连续块面扫描电子显微镜可以实现这一点，并且在离体灌注人眼中观察到的微分段流动模式提示了一种假设机制。
