Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA. Electronic address: http://www.OcularBiomechanics.com.
Acta Biomater. 2018 May;72:295-305. doi: 10.1016/j.actbio.2018.03.026. Epub 2018 Mar 21.
Our goal was to quantify and characterize how the collagen fiber crimp waviness of the lamina cribrosa (LC) and peripapillary sclera (PPS) changes with intraocular pressure (IOP). Thirteen sheep (ovine) eyes were immersion and perfusion fixed while maintaining IOP at 0, 10, 15, 20, or 50 mmHg. Coronal optic nerve head (ONH) sections (30 µm) were imaged with polarized light microscopy (PLM) and analyzed for collagen fiber orientation and waviness (SD of fiber orientation). In the LC, the waviness of every LC beam was measured. In the PPS, at least 900 collagen bundles were measured per eye. Using the waviness at 50 mmHg IOP, we defined tissue-specific thresholds to determine the fraction of loaded or recruited fibers. We found that fiber waviness decreased with IOP (P < 0.001). At every IOP, the waviness of the collagen fibers, and the fraction of fibers recruited in the LC were smaller or equal than those of the PPS (P < 0.001). At 15 mmHg IOP, both LC and PPS had ¾ recruited fibers and ¼ left in reserve. The decreased waviness with IOP and associated fiber recruitment is experimental evidence of fiber-based nonlinear biomechanical behavior of the ONH. At all IOPs the PPS had an equal or larger fraction of fibers recruited than the LC. That both LC and PPS had the same fraction of recruited and reserve fibers at normal IOP suggests that this may be an optimal fraction of recruitment for healthy eyes. Whether this extends to human eyes remains unknown.
Collagen fibers exhibit a natural waviness or crimp that largely determine the nonlinear biomechanics of soft tissue. Experimental measurements of crimp morphology in the sheep eye, and how it changes with intraocular pressure (IOP), however, are exceedingly sparse. We quantified how posterior eye crimp changes with increasing IOP. We found that the lamina cribrosa and peripapillary sclera have fundamentally different crimp, and with increasing IOP, have different proportions of fibers that straighten, or get recruited, versus remaining wavy, or in reserve. Interestingly, at physiologic IOP of 15 mmHg, both tissues had about ¾ fibers recruited and ¼ fibers in reserve, indicating there may be an optimal fraction of fibers.
我们的目标是定量和描述小梁网（LC）和视乳头周围巩膜（PPS）的胶原纤维卷曲波纹如何随眼压（IOP）而变化。将 13 只绵羊（羊）的眼睛浸入并灌注固定，同时将 IOP 维持在 0、10、15、20 或 50mmHg。用偏光显微镜（PLM）对冠状视神经头（ONH）切片（30μm）进行成像，并分析胶原纤维取向和波纹（纤维取向的标准差）。在 LC 中，测量了每个 LC 束的波纹。在 PPS 中，每只眼睛至少测量 900 个胶原束。使用 50mmHgIOP 的波纹，我们定义了组织特异性阈值来确定加载或募集纤维的分数。我们发现纤维波纹随 IOP 降低（P<0.001）。在每个 IOP 下，LC 和 PPS 的胶原纤维波纹以及募集纤维的分数均小于或等于 PPS（P<0.001）。在 15mmHgIOP 时，LC 和 PPS 均有 ¾募集纤维和¼纤维处于储备状态。IOP 下的波纹减小和相关纤维募集是 ONH 基于纤维的非线性生物力学行为的实验证据。在所有 IOP 下，PPS 的募集纤维分数都相等或大于 LC。在正常 IOP 下，LC 和 PPS 的募集纤维分数相等或更大，这表明这可能是健康眼睛的最佳募集纤维分数。这是否扩展到人类眼睛尚不清楚。
