Moffat B A, Atchison D A, Pope J M
Centre for Medical, Health and Environmental Physics, Queensland University of Technology, G.P.O. Box 2434, 4001, Brisbane, Australia.
Vision Res. 2002 Jun;42(13):1683-93. doi: 10.1016/s0042-6989(02)00078-0.
We report a new technique for non-invasively mapping the refractive index distribution through the eye lens using magnetic resonance micro-imaging. The technique is applied to map the refractive index distribution throughout the sagittal plane of 18 human eye lenses ranging in age from 14 to 82 years in vitro. The results are compared with standard models for the human eye lens. They confirm that the refractive index distribution, when plotted as a function of normalised lens radius, is a function of lens age and differs both between the equatorial and axial directions and between the anterior and posterior halves of the optical axis. The refractive index of the lens nucleus exhibits a significant reduction with age amounting to 3.4+/-0.6 x 10(-4) years(-1). The contribution of the gradient index (GRIN) to the lens power decreases by 0.286+/-0.067 D/year, accounting almost entirely for the estimated overall change in lens power with age for these lenses, which were probably in their most accommodated state. The results provide experimental verification of hypothesised changes in the GRIN that have previously been invoked as contributing to presbyopia and support the hypothesis that changes in the GRIN are sufficient to offset effects of increasing curvature of human lenses with age in their unaccommodated state.
我们报告了一种利用磁共振显微成像技术非侵入性地绘制人眼晶状体折射率分布的新技术。该技术被应用于体外绘制18个人眼晶状体矢状面的折射率分布，这些晶状体年龄从14岁到82岁不等。将结果与人类晶状体的标准模型进行比较。结果证实，当将折射率分布绘制为归一化晶状体半径的函数时，它是晶状体年龄的函数，并且在赤道方向和轴向之间以及光轴的前半部分和后半部分之间均有所不同。晶状体核的折射率随年龄显著降低，降低幅度为3.4±0.6×10⁻⁴/年。梯度折射率（GRIN）对晶状体屈光力的贡献每年降低0.286±0.067 D，几乎完全解释了这些晶状体（可能处于最调节状态）随年龄增长的晶状体屈光力总体变化。这些结果为先前被认为与老花眼有关的GRIN假设变化提供了实验验证，并支持GRIN变化足以抵消人晶状体在非调节状态下随年龄增长曲率增加的影响这一假设。
