Contribution of the gradient refractive index and shape to the crystalline lens spherical aberration and astigmatism
Contribution of the gradient refractive index and shape to the crystalline lens spherical aberration and astigmatism
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DOI：
10.1016/j.visres.2013.04.004
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发表时间：
2013-06-28
期刊：
影响因子：
1.8
通讯作者：
Marcos, Susana
中科院分区：
文献类型：
--
作者：
Birkenfeld, Judith;de Castro, Alberto;Marcos, Susana
晶体透镜的光学性能是由其形状和折射率分布决定的。然而，到目前为止，这些特性还没有在同一个透镜中一起测量，因此它们对光学像差的相对贡献还没有完全了解。采用光学相干断层扫描（optical Coherence Tomography）和激光示踪（laser ray tracing）技术，在体外测量了10只6月龄左右的猪晶体的形状、光程差和焦距。采用基于遗传算法的优化方法重构了三维梯度折射率分布。该优化方法在18条不同经络中寻找最适合晶状体变形后表面的4变量GRIN模型参数。利用等效均匀折射率重构的GRIN透镜，利用计算射线追迹估计了透镜的球差和像散。所有晶状体的后曲率半径均明显大于前曲率半径，前、后正表面的圆锥常数均为正。平均而言，测量焦距随瞳孔直径的增大而增大，与晶状体负球差一致。在633 nm处，重建了原子核和表面的折射率平均值，分别为1.427和1.364。GRIN重建结果显示，所有透镜样品的折射率分布都很广。与均匀指数相比，GRIN将球差移向负值。负球差与GRIN被发现在10个镜头中的8个。GRIN的存在也使大多数透镜的散光总量减少，而散光轴受GRIN的影响很小。据我们所知，这项研究是第一个系统的实验研究几何形状和GRIN对哺乳动物晶状体像差的相对贡献。(C) 2013 Elsevier Ltd.版权所有。
The optical properties of the crystalline lens are determined by its shape and refractive index distribution. However, to date, those properties have not been measured together in the same lens, and therefore their relative contributions to optical aberrations are not fully understood. The shape, the optical path difference, and the focal length of ten porcine lenses (age around 6 months) were measured in vitro using Optical Coherence Tomography and laser ray tracing. The 3D Gradient Refractive Index distribution (GRIN) was reconstructed by means of an optimization method based on genetic algorithms. The optimization method searched for the parameters of a 4-variable GRIN model that best fits the distorted posterior surface of the lens in 18 different meridians. Spherical aberration and astigmatism of the lenses were estimated using computational ray tracing, with the reconstructed GRIN lens and an equivalent homogeneous refractive index. For all lenses the posterior radius of curvature was systematically steeper than the anterior one, and the conic constant of both the anterior and posterior positive surfaces was positive. In average, the measured focal length increased with increasing pupil diameter, consistent with a crystalline lens negative spherical aberration. The refractive index of nucleus and surface was reconstructed to an average value of 1.427 and 1.364, respectively, for 633 nm. The results of the GRIN reconstruction showed a wide distribution of the index in all lens samples. The GRIN shifted spherical aberration towards negative values when compared to a homogeneous index. A negative spherical aberration with GRIN was found in 8 of the 10 lenses. The presence of GRIN also produced a decrease in the total amount of lens astigmatism in most lenses, while the axis of astigmatism was only little influenced by the presence of GRIN. To our knowledge, this study is the first systematic experimental study of the relative contribution of geometry and GRIN to the aberrations in a mammal lens. (C) 2013 Elsevier Ltd. All rights reserved.