Department of Radiology, Weill Cornell Medicine, New York, NY, USA.
Vision Sciences, School of Psychological Sciences, College of Engineering, Science, and Environment, The University of Newcastle, Callaghan, NSW, Australia.
Exp Eye Res. 2022 Nov;224:109165. doi: 10.1016/j.exer.2022.109165. Epub 2022 Jul 8.
Myopia alters the microstructural and biomechanical properties of the posterior sclera, which is characterized as a layered structure with potentially different inter-layer collagen fibril characteristics. Scanning acoustic microscopy (SAM) has been used to investigate how the micron-scale bulk mechanical properties of the posterior sclera are affected by myopia. Other investigators have employed second harmonic generation (SHG) imaging to characterize the collagen microstructure of tissues. In the present study, SAM and SHG imaging were used to investigate the existence of biomechanically-distinct scleral layers and identify relationships between mechanical properties and tissue microstructure in myopic guinea pig (GP) eyes. Diffusers were worn over the right eyes of six, 1-week-old GPs for one week to induce unilateral form-deprivation myopia. GPs were euthanized, enucleated, and eyes were cryosectioned. Twelve-micron-thick adjacent vertical cryosections were scanned with SAM or SHG. SAM maps of bulk modulus, mass density, and acoustic attenuation were estimated. A fiber-extraction algorithm applied to SHG images estimated collagen fiber length, width, straightness, alignment, and number density. Results revealed that the posterior sclera may exhibit biomechanically distinct layers that are affected differently in myopia. Specifically, a layered structure was observed in the mechanical-parameter maps of control eyes that was less apparent in myopic eyes. Collagen fibers in myopic eyes had smaller diameters and were more aligned. Myopia-associated biomechanical changes were most significant in the outermost and innermost scleral layers. SAM-measured mechanical parameters were correlated with collagen fiber microstructure, particularly fiber length, alignment, and number density, which may imply the biomechanical parameters estimated from SAM measurements are related to tissue microstructure. Interestingly, some changes were greatest in more-peripheral regions, suggesting interventions to strengthen the sclera may be effective away from the optic nerve and efficacy may be achieved best when intervention is applied to the outermost layer.
近视改变了后巩膜的微观结构和生物力学特性，后巩膜具有分层结构，各层之间的胶原纤维特征可能存在差异。扫描声学显微镜（SAM）已被用于研究近视如何影响后巩膜的微米级整体力学性能。其他研究人员采用二次谐波产生（SHG）成像来描述组织的胶原微观结构。在本研究中，SAM 和 SHG 成像用于研究是否存在具有不同生物力学特性的巩膜层，并确定近视豚鼠（GP）眼中机械特性和组织微观结构之间的关系。为了诱导单侧形觉剥夺性近视，在 6 只 1 周龄 GP 的右眼上佩戴扩散器一周。处死 GP，眼球摘出，冷冻切片。用 SAM 或 SHG 对 12 微米厚的相邻垂直冷冻切片进行扫描。估计了体模量、质量密度和声衰减的 SAM 图谱。应用于 SHG 图像的纤维提取算法估计了胶原纤维长度、宽度、直度、取向和数量密度。结果表明，后巩膜可能表现出具有不同生物力学特性的分层，近视对这些分层的影响不同。具体而言，在对照眼的力学参数图中观察到分层结构，而在近视眼中则不太明显。近视眼中的胶原纤维直径较小，取向更一致。近视相关的生物力学变化在外层和最内层巩膜层最为显著。SAM 测量的力学参数与胶原纤维微观结构相关，特别是纤维长度、取向和数量密度，这可能意味着从 SAM 测量估计的生物力学参数与组织微观结构有关。有趣的是，一些变化在外周区域最大，这表明强化巩膜的干预措施可能在远离视神经的部位有效，并且当干预应用于最外层时，可能会获得最佳效果。
