Daxer A, Misof K, Grabner B, Ettl A, Fratzl P
Universitätsklinik für Augenheilkunde, Innsbruck, Austria.
Invest Ophthalmol Vis Sci. 1998 Mar;39(3):644-8.
Transparency and biomechanical properties of the cornea depend on the structure and organization of collagen fibrils. The authors determined diameter, axial period, and lateral molecular spacing of collagen fibrils in human corneal stroma as a function of age.
Seventeen normal human corneas were investigated in their native state by means of small-angle and wide-angle x-ray scattering.
The mean radius of collagen fibrils, the axial period of collagen fibrils, and the lateral intermolecular Bragg spacing were found to be age dependent. The authors determined fibril radii of 16.1 +/- 0.5 nm in persons older than 65 years of age (n = 10) and 15.4 +/- 0.5 nm (mean +/- SD) in persons younger than 65 years (n = 7) (P < 0.022). The related age-dependent values were 66.4 +/- 0.7 nm (> 65 years) and 65.2 +/- 0.8 nm (< 65 years) for the axial period (P < 0.006) and 1.515 +/- 0.010 nm (> 65 years) and 1.499 +/- 0.013 nm (< 65 years) for the intermolecular Bragg spacing (P < 0.022).
Aging is related to a three-dimensional growth of collagen fibrils in the human corneal stroma. The age-related growth of the fibril diameter was mostly a result of an increased number of collagen molecules and, in addition, to some expansion of the intermolecular Bragg spacing probably resulting from glycation-induced cross-linking. The observed expansion of the fibrils in an axial direction may result from reduction of the molecular tilting angle within collagen fibrils. The observed alterations of the collagen framework may have implications for refractive surgery and ocular tonometry achieved through related changes in the biomechanical properties of the cornea.
角膜的透明度和生物力学特性取决于胶原纤维的结构和组织。作者测定了人角膜基质中胶原纤维的直径、轴向周期和横向分子间距随年龄的变化。
采用小角和广角X射线散射对17个正常人类角膜的天然状态进行研究。
发现胶原纤维的平均半径、胶原纤维的轴向周期和横向分子布拉格间距与年龄有关。作者测定65岁以上人群（n = 10）的纤维半径为16.1±0.5 nm，65岁以下人群（n = 7）为15.4±0.5 nm（平均值±标准差）（P < 0.022）。轴向周期的相关年龄依赖性值在65岁以上人群为66.4±0.7 nm，65岁以下人群为65.2±0.8 nm（P < 0.006）；分子布拉格间距在65岁以上人群为1.515±0.010 nm，65岁以下人群为1.499±0.013 nm（P < 0.022）。
衰老与人角膜基质中胶原纤维的三维生长有关。与年龄相关的纤维直径增长主要是胶原分子数量增加的结果，此外，分子布拉格间距的一些扩大可能是糖基化诱导交联所致。观察到的纤维在轴向上的扩张可能是由于胶原纤维内分子倾斜角减小所致。观察到的胶原框架改变可能对屈光手术和通过角膜生物力学特性的相关变化实现的眼压测量有影响。
