Department of Mechanical Engineering, Johns Hopkins University, 3400 North Charles St., Latrobe 125, Baltimore, MD 21218, USA.
Exp Eye Res. 2010 Dec;91(6):866-75. doi: 10.1016/j.exer.2010.09.009. Epub 2010 Sep 22.
The purpose of this research was to develop a reliable and repeatable inflation protocol to measure the scleral inflation response of mouse eyes to elevations in intraocular pressure (IOP), comparing the inflation response exhibited by the sclera of younger and older C57BL/6 mice. Whole, enucleated eyes from younger (2 month) and older (11 month) C57BL/6 mice were mounted by the cornea on a custom fixture and inflated according to a load-unload, ramp-hold pressurization regimen via a cannula connected to a saline-filled programmable syringe pump. First, the tissue was submitted to three load-unload cycles from 6 mmHg to 15 mmHg at a rate of 0.25 mmHg/s with ten minutes of recovery between cycles. Next the tissue was submitted to a series of ramp-hold tests to measure the creep behavior at different pressure levels. For each ramp-hold test, the tissue was loaded from 6 mmHg to the set pressure at a rate of 0.25 mmHg/s and held for 30 min, and then the specimens were unloaded to 6 mmHg for 10 min. This sequence was repeated for set pressures of: 10.5, 15, 22.5, 30, 37.5, and 45 mmHg. Scleral displacement was measured using digital image correlation (DIC), and fresh scleral thickness was measured optically for each specimen after testing. For comparison, scleral thickness was measured on untested fresh tissue and epoxy-fixed tissue from age-matched animals. Comparing the apex displacement of the different aged specimens, the sclera of older animals had a statistically significant stiffer response to pressurization than the sclera of younger animals. The stiffness of the pressure-displacement response of the apex measured in the small-strain (6-15 mmHg) and the large-strain (37.5-45 mmHg) regime, respectively, were 287 ± 100 mmHg/mm and 2381 ± 191 mmHg/mm for the older tissue and 193 ± 40 mmHg/mm and 1454 ± 93 mmHg/mm for the younger tissue (Student t-test, p<0.05). The scleral thickness varied regionally, being thickest in the peripapillary region and thinnest at the equator. Fresh scleral thickness did not differ significantly by age in this group of animals. This study presents a reliable inflation test protocol to measure the mechanical properties of mouse sclera. The inflation methodology was sensitive enough to measure scleral response to changes in IOP elevations between younger and older C57BL/6 mice. Further, the specimen-specific scleral displacement profile and thickness measurements will enable future development of specimen-specific finite element models to analyze the inflation data for material properties.
本研究旨在开发一种可靠且可重复的膨胀方案，以测量小鼠眼球巩膜对眼内压（IOP）升高的膨胀反应，比较年轻和老年 C57BL/6 小鼠巩膜的膨胀反应。将来自年轻（2 个月）和老年（11 个月）C57BL/6 小鼠的整个去眼组织通过角膜安装在定制夹具上，并通过连接到充满生理盐水的可编程注射器泵的套管进行加载-卸载、斜坡保持加压方案进行充气。首先，组织在 0.25mmHg/s 的速率下从 6mmHg 到 15mmHg 经历三个加载-卸载循环，每个循环之间有十分钟的恢复时间。接下来，组织进行了一系列斜坡保持测试，以测量不同压力水平下的蠕变行为。对于每个斜坡保持测试，组织以 0.25mmHg/s 的速率从 6mmHg 加载到设定压力，并保持 30 分钟，然后将标本卸载至 6mmHg 10 分钟。该序列针对设定压力重复进行：10.5、15、22.5、30、37.5 和 45mmHg。使用数字图像相关（DIC）测量巩膜位移，并在测试后使用光学方法测量每个标本的新鲜巩膜厚度。为了比较，对年龄匹配动物的未经测试的新鲜组织和环氧固定组织进行了巩膜厚度测量。比较不同年龄标本的顶点位移，发现老年动物的巩膜对加压的反应明显比年轻动物的巩膜更硬。在小应变（6-15mmHg）和大应变（37.5-45mmHg）范围内分别测量顶点的压力-位移响应的刚度，分别为 287±100mmHg/mm 和 2381±191mmHg/mm 为老年组织，193±40mmHg/mm 和 1454±93mmHg/mm 为年轻组织（学生 t 检验，p<0.05）。巩膜厚度存在区域性差异，在视盘周围区域最厚，在赤道处最薄。在这群动物中，新鲜巩膜厚度与年龄无显著差异。本研究提出了一种可靠的膨胀测试方案，用于测量小鼠巩膜的力学性能。该膨胀方法足够灵敏，可以测量年轻和老年 C57BL/6 小鼠之间眼内压升高引起的巩膜反应。此外，特定标本的巩膜位移曲线和厚度测量将能够为未来的特定标本有限元模型开发提供支持，以分析膨胀数据的材料特性。
