Department of Ophthalmology, Columbia University Medical Center, New York, NY, 10032, USA; Singapore Eye Research Institute, Singapore National Eye Centre, Duke-NUS Medical School, Singapore.
Lizzi Center for Biomedical Engineering, Riverside Research, New York, NY, 10038, USA.
Exp Eye Res. 2019 Sep;186:107739. doi: 10.1016/j.exer.2019.107739. Epub 2019 Jul 19.
Biomechanical changes in the sclera likely underlie the excessive eye elongation of axial myopia. We studied the biomechanical characteristics of myopic sclera at the microscopic level using scanning acoustic microscopy (SAM) with 7-μm in-plane resolution. Guinea pigs underwent form-deprivation (FD) in one eye from 4 to 12 days of age to induce myopia, and 12-μm-thick scleral cryosections were scanned using a custom-made SAM. Two-dimensional maps of the bulk modulus (K) and mass density (ρ) were derived from the SAM data using a frequency-domain approach. We assessed the effect on K and ρ exerted by: 1) level of induced myopia, 2) region (superior, inferior, nasal or temporal) and 3) eccentricity from the nerve using univariate and multivariate regression analyses. Induced myopia ranged between -3D and -9.3D (Mean intraocular difference of -6.2 ± 1.7D, N = 11). K decreased by 0.036 GPa for every 1.0 D increase in induced myopia across vertical sections (p < 0.001). Among induced myopia right eyes, K values in the inherently more myopic superior region were 0.088 GPa less than the inferior region (p = 0.002) and K in the proximal nasal region containing the central axis were 0.10 GPa less than temporal K (p = 0.036). K also increased 0.12 GPa for every 1 mm increase in superior vertical distance (p < 0.001), an effect that was blunted after 1 week of FD. Overall, trends for ρ were less apparent than for K. ρ values increased by 20.7 mg/cm for every 1.00 D increase in induced myopia across horizontal sections (p < 0.001), and were greatest in the region containing the central posterior pole. ρ values in the inherently more myopic superior region were 13.1 mg/cm greater than that found in inferior regions among control eyes (p = 0.002), and increased by 11.2 mg/cm for every 1 mm increase in vertical distance (p = 0.001). This peripheral increase in ρ was blunted after 1 week of FD. Scleral material properties vary depending on the location in the sclera and the level of induced myopia. Bulk modulus was most reduced in the most myopic regions (both induced myopia and inherent regional myopia), and suggests that FD causes microscopic local decreases in sclera stiffness, while scleral mass density was most increased in the most myopic regions.
巩膜的生物力学变化可能是轴性近视眼球过度伸长的基础。我们使用具有 7 µm 面内分辨率的扫描声学显微镜 (SAM) 在微观水平上研究了近视巩膜的生物力学特性。从 4 到 12 天龄起，豚鼠的一只眼睛经历形觉剥夺 (FD) 以诱导近视，然后使用定制的 SAM 扫描 12 µm 厚的巩膜冷冻切片。使用频域方法从 SAM 数据中得出体积模量 (K) 和质量密度 (ρ) 的二维图。我们使用单变量和多变量回归分析评估了以下因素对 K 和 ρ 的影响：1）诱导的近视程度，2）区域（上方、下方、鼻侧或颞侧）和 3）距神经的偏心度。诱导的近视范围为 -3D 至 -9.3D（Mean 眼内差异为-6.2 ± 1.7D，N = 11）。K 随着垂直截面每增加 1.0D 的诱导近视而降低 0.036GPa（p<0.001）。在诱导性近视的右眼，固有更近视的上方区域的 K 值比下方区域低 0.088GPa（p=0.002），并且包含中央轴的近鼻侧区域的 K 值比颞侧 K 值低 0.10GPa（p=0.036）。K 还随着上方垂直距离每增加 1mm 而增加 0.12GPa（p<0.001），这种影响在 FD 1 周后减弱。总体而言，与 K 相比，ρ 的趋势不太明显。ρ 值在水平切片中随着每增加 1.00D 的诱导近视而增加 20.7mg/cm（p<0.001），并且在包含中央后极的区域最大。在固有更近视的上方区域，ρ 值比对照眼的下方区域高 13.1mg/cm（p=0.002），并且随着垂直距离每增加 1mm，ρ 值增加 11.2mg/cm（p=0.001）。这种在 FD 1 周后减弱的外周 ρ 增加。巩膜材料特性取决于巩膜中的位置和诱导近视的程度。体积模量在最近视的区域（诱导性近视和固有区域性近视）中降低最多，这表明 FD 导致巩膜刚度的微观局部降低，而巩膜质量密度在最近视的区域增加最多。
