College of Medicine, The Ohio State University, Ohio, USA.
Exp Eye Res. 2011 Dec;93(6):825-32. doi: 10.1016/j.exer.2011.09.018. Epub 2011 Oct 5.
Intraocular pressure (IOP) fluctuations have gained recent clinical interest and thus warrant an understanding of how the sclera responds to dynamic mechanical insults. The objective of this study was to characterize the regional dynamic viscoelastic properties of canine sclera under physiological cyclic loadings. Scleral strips were excised from the anterior, equatorial, and posterior sclera in ten canine eyes. The dimensions of each strip were measured using a high resolution ultrasound imaging system. The strips were tested in a humidity chamber at approximately 37 °C using a Rheometrics Systems Analyzer. A cyclic strain input (0.25%, 1 Hz) was applied to the strips, superimposed upon pre-stresses corresponding to an IOP of 15, 25, and 45 mmHg. The cyclic stress output was recorded and the dynamic properties were calculated based on linear viscoelasticity. Uni-axial tensile tests were also performed on the same samples and the results were compared to those reported for human eyes. The results showed that the sclera's resistance to dynamic loading increased significantly while the damping capability decreased significantly with increasing pre-stresses for all regions of sclera (P < 0.001). Anterior sclera appeared to have a significantly higher damping capability than equatorial and posterior sclera (P = 0.003 and 0.018, respectively). The secant modulus from uni-axial tensile tests showed a decreasing trend from anterior to posterior sclera, displaying a similar pattern as in the human eye. In conclusion, all scleral regions in the canine eyes exhibited an increased ability to resist and a decreased ability to dampen cyclic stress insults at increasing pre-stress (i.e., increasing steady-state IOP). The regional variation of the dynamic properties differed from those of uni-axial tensile tests. Dynamic testing may provide useful information to better understand the mechanical behavior of the sclera in response to dynamic IOP.
眼压（IOP）波动近来受到临床关注，因此有必要了解巩膜对动态力学损伤的反应。本研究旨在表征犬巩膜在生理循环负荷下的区域性动态粘弹性特性。从前部、赤道部和后部巩膜切取 10 只犬眼的巩膜条。使用高分辨率超声成像系统测量每条带的尺寸。在大约 37°C 的湿度室中，在 Rheometrics Systems Analyzer 上进行测试。将循环应变输入（0.25%，1Hz）施加到条带上，叠加在对应于 15、25 和 45mmHgIOP 的预应力度上。记录循环应力输出，并根据线性粘弹性计算动态特性。还对相同的样本进行了单轴拉伸测试，并将结果与报告的人类眼睛结果进行了比较。结果表明，随着所有巩膜区域的预应力度增加，巩膜对动态加载的抵抗力显著增加，而阻尼能力显著降低（P<0.001）。与赤道部和后部巩膜相比，前部巩膜似乎具有更高的阻尼能力（P=0.003 和 0.018）。单轴拉伸测试的割线模量显示出从前部到后部巩膜的降低趋势，与人类眼睛的模式相似。总之，犬眼的所有巩膜区域在增加的预应力度（即稳态 IOP）下表现出抵抗能力增加和阻尼能力降低的能力，以抵抗循环应力损伤。动态特性的区域变化与单轴拉伸测试不同。动态测试可能提供有用的信息，以更好地了解巩膜对动态 IOP 的机械行为。
