Coudrillier Baptiste, Pijanka Jacek, Jefferys Joan, Sorensen Thomas, Quigley Harry A, Boote Craig, Nguyen Thao D
J Biomech Eng. 2015 Jul;137(7):0710071-07100710. doi: 10.1115/1.4029986. Epub 2015 Jun 2.
The effects of diabetes on the collagen structure and material properties of the sclera are unknown but may be important to elucidate whether diabetes is a risk factor for major ocular diseases such as glaucoma. This study provides a quantitative assessment of the changes in scleral stiffness and collagen fiber alignment associated with diabetes. Posterior scleral shells from five diabetic donors and seven non-diabetic donors were pressurized to 30 mm Hg. Three-dimensional surface displacements were calculated during inflation testing using digital image correlation (DIC). After testing, each specimen was subjected to wide-angle X-ray scattering (WAXS) measurements of its collagen organization. Specimen-specific finite element models of the posterior scleras were generated from the experimentally measured geometry. An inverse finite element analysis was developed to determine the material properties of the specimens, i.e., matrix and fiber stiffness, by matching DIC-measured and finite element predicted displacement fields. Effects of age and diabetes on the degree of fiber alignment, matrix and collagen fiber stiffness, and mechanical anisotropy were estimated using mixed effects models accounting for spatial autocorrelation. Older age was associated with a lower degree of fiber alignment and larger matrix stiffness for both diabetic and non-diabetic scleras. However, the age-related increase in matrix stiffness was 87% larger in diabetic specimens compared to non-diabetic controls and diabetic scleras had a significantly larger matrix stiffness (p = 0.01). Older age was associated with a nearly significant increase in collagen fiber stiffness for diabetic specimens only (p = 0.06), as well as a decrease in mechanical anisotropy for non-diabetic scleras only (p = 0.04). The interaction between age and diabetes was not significant for all outcomes. This study suggests that the age-related increase in scleral stiffness is accelerated in eyes with diabetes, which may have important implications in glaucoma.
糖尿病对巩膜胶原结构和材料特性的影响尚不清楚，但对于阐明糖尿病是否是青光眼等主要眼部疾病的危险因素可能很重要。本研究对与糖尿病相关的巩膜硬度和胶原纤维排列变化进行了定量评估。对来自5名糖尿病供体和7名非糖尿病供体的后巩膜壳施加30毫米汞柱的压力。在充气测试期间，使用数字图像相关技术（DIC）计算三维表面位移。测试后，对每个标本进行广角X射线散射（WAXS）测量，以分析其胶原组织。根据实验测量的几何形状生成后巩膜的特定标本有限元模型。通过匹配DIC测量的和有限元预测的位移场，开发了一种逆有限元分析来确定标本的材料特性，即基质和纤维硬度。使用考虑空间自相关的混合效应模型估计年龄和糖尿病对纤维排列程度、基质和胶原纤维硬度以及机械各向异性的影响。对于糖尿病和非糖尿病巩膜，年龄较大与较低的纤维排列程度和较大的基质硬度相关。然而，与非糖尿病对照组相比，糖尿病标本中与年龄相关的基质硬度增加要大87%，并且糖尿病巩膜的基质硬度明显更大（p = 0.01）。仅糖尿病标本中，年龄较大与胶原纤维硬度几乎显著增加相关（p = 0.06），仅非糖尿病巩膜中，年龄较大与机械各向异性降低相关（p = 0.04）。年龄和糖尿病之间的相互作用对所有结果均不显著。本研究表明，糖尿病患者的眼睛中，与年龄相关的巩膜硬度增加会加速，这可能对青光眼具有重要意义。
