Shin Andrew, Park Joseph, Demer Joseph L
Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, United States; Wellman Center for Photomedicine, Harvard Medical School & Massachusetts General Hospital, Boston, United States.
Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, United States; Department of Bioengineering, University of California, Los Angeles, United States.
J Biomech. 2018 Apr 27;72:173-179. doi: 10.1016/j.jbiomech.2018.03.017. Epub 2018 Mar 15.
Polarization sensitive optical coherence tomography (PSOCT) is an interferometric technique sensitive to birefringence. Since mechanical loading alters the orientation of birefringent collagen fibrils, we asked if PSOCT can be used to measure local mechanical properties of sclera. Infrared (1300 nm) PSOCT was performed during uniaxial tensile loading of fresh scleral specimens of rabbits, cows, and humans from limbal, equatorial, and peripapillary regions. Specimens from 8 human eyes were obtained. Specimens were stretched to failure at 0.01 mm/s constant rate under physiological conditions of temperature and humidity while birefringence was computed every 117 ms from cross-sectional PSOCT. Birefringence modulus (BM) was defined as the rate of birefringence change with strain, and tensile modulus (TM) as the rate of stress change between 0 and 9% strain. In cow and rabbit, BM and TM were positively correlated with slopes of 0.17 and 0.10 GPa, and with correlation coefficients 0.63 and 0.64 (P < 0.05), respectively, following stress-optic coefficients 4.69, and 4.20 GPa. In human sclera, BM and TM were also positively correlated with slopes of 0.24 GPa for the limbal, 0.26 GPa for the equatorial, and 0.31 GPa for the peripapillary regions. Pearson correlation coefficients were significant at 0.51, 0.58, and 0.69 for each region, respectively (<0.001). Mean BM decreased proportionately to TM from the limbal to equatorial to peripapillary regions, as stress-optic coefficients were estimated as 2.19, 2.42, and 4.59 GPa, respectively. Since birefringence and tensile elastic moduli correlate differently in cow, rabbit, and various regions of human sclera, it might be possible to mechanically characterize the sclera in vivo using PSOCT.
偏振敏感光学相干断层扫描（PSOCT）是一种对双折射敏感的干涉测量技术。由于机械负荷会改变双折射胶原纤维的取向，我们探讨了PSOCT是否可用于测量巩膜的局部力学特性。在对来自兔、牛和人类角膜缘、赤道和视乳头周围区域的新鲜巩膜标本进行单轴拉伸负荷时，进行了红外（1300纳米）PSOCT检查。获取了8只人眼的标本。在温度和湿度的生理条件下，以0.01毫米/秒的恒定速率将标本拉伸至破坏，同时每隔117毫秒从横截面PSOCT计算双折射。双折射模量（BM）定义为双折射随应变的变化率，拉伸模量（TM）定义为0至9%应变之间应力的变化率。在牛和兔中，BM和TM分别与斜率0.17和0.10吉帕呈正相关，相关系数分别为0.63和0.64（P<0.05），应力-光学系数分别为4.69和4.20吉帕。在人巩膜中，BM和TM在角膜缘区域也与斜率0.24吉帕呈正相关，赤道区域为0.26吉帕，视乳头周围区域为0.31吉帕。每个区域的皮尔逊相关系数分别为0.51、0.58和0.69，均具有显著性（<0.001）。从角膜缘到赤道再到视乳头周围区域，平均BM与TM成比例下降，因为应力-光学系数分别估计为2.19、2.42和4.59吉帕。由于双折射和拉伸弹性模量在牛、兔和人巩膜的不同区域中具有不同的相关性，因此有可能使用PSOCT在体内对巩膜进行力学特征描述。
