Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA.
Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.
Acta Biomater. 2018 Oct 1;79:113-122. doi: 10.1016/j.actbio.2018.08.020. Epub 2018 Aug 21.
The collagen fiber architecture of the peripapillary sclera (PPS), which surrounds the scleral canal, is a critical factor in determining the mechanical response of the optic nerve head (ONH) to variations in intraocular pressure (IOP). Experimental and clinical evidence point to IOP-induced deformations within the scleral canal as important contributing factors of glaucomatous neural tissue damage and consequent vision loss. Hence, it is imperative to understand PPS architecture and biomechanics. Current consensus is that the fibers of the PPS form a closed ring around the canal to support the delicate neural tissues within. We propose an alternative fiber architecture for the PPS, in which the scleral canal is supported primarily by long-running fibers oriented tangentially to the canal. We present evidence that this tangential model is consistent with histological observations in multiple species, and with quantitative measurements of fiber orientation obtained from small angle light scattering and wide-angle X-ray scattering. Using finite element models, we investigated the biomechanical implications of a tangential fiber PPS architecture. We found that the tangential arrangement of fibers afforded better mechanical support to the tissues within the scleral canal as compared to a simple circumferential ring of fibers or a combination of fibers oriented radially and circumferentially. We also found that subtle variations from a tangential orientation could reproduce clinically observed ONH behavior which has yet to be explained using current theories of PPS architecture and simulation, namely, the contraction of the scleral canal under elevated IOP.
It is hypothesized that vision loss in glaucoma is due to excessive mechanical deformation within the neural tissue inside the scleral canal. This study proposes a new model for how the collagen of the peripapillary sclera surrounding the canal is organized to support the delicate neural tissue inside. Previous low-resolution studies of the peripapillary sclera suggested that the collagen fibers are arranged in a ring around the canal. Instead, we provide microscopic evidence suggesting that the canal is also supported by long-running interwoven fibers oriented tangentially to the canal. We demonstrate that this arrangement has multiple biomechanical advantages over a circular collagen arrangement and can explain previously unexplained experimental findings including contraction of the scleral canal under elevated intraocular pressure.
围绕着巩膜管的视盘周围巩膜（PPS）的胶原纤维结构是决定视神经头（ONH）对眼内压（IOP）变化的机械反应的关键因素。实验和临床证据表明，巩膜管内的IOP 诱导变形是青光眼神经组织损伤和随后视力丧失的重要因素。因此，了解 PPS 结构和生物力学至关重要。目前的共识是，PPS 的纤维形成围绕着管的封闭环，以支撑管内的精细神经组织。我们提出了一种 PPS 的替代纤维结构，其中巩膜管主要由沿管切线方向延伸的长纤维支撑。我们提出的证据表明，这种切线模型与多种物种的组织学观察结果以及从小角度光散射和广角 X 射线散射获得的纤维取向定量测量结果一致。使用有限元模型，我们研究了切线纤维 PPS 结构的生物力学意义。我们发现，与简单的环形纤维或径向和环形纤维组合相比，纤维的切线排列为巩膜管内的组织提供了更好的机械支撑。我们还发现，从切线方向的细微变化可以再现临床上观察到的 ONH 行为，而目前的 PPS 结构和模拟理论尚未对此进行解释，即，在眼压升高下巩膜管的收缩。
据推测，青光眼的视力丧失是由于巩膜管内的神经组织发生过度机械变形所致。这项研究提出了一种新的模型，用于解释围绕管的视盘周围巩膜的胶原如何组织以支撑管内的精细神经组织。先前对视盘周围巩膜的低分辨率研究表明，胶原纤维呈环形排列在管周围。相反，我们提供了微观证据，表明管也由沿管切线方向延伸的交织长纤维支撑。我们证明，与圆形胶原排列相比，这种排列具有多个生物力学优势，并且可以解释以前无法解释的实验结果，包括在眼压升高下巩膜管的收缩。
