基于Zemax接口技术的人眼晶状体模型研究

对人眼模型中晶状体的面型和折射率分布进行了研究,基于晶状体的光学特性,利用光学设计软件Zemax接口技术的调入,采用不同连续公式法分别给出了晶状体不同的梯度渐变折射率分布形式;结合晶状体不同的非球面面型,比较分析了晶状体不同面型和不同梯度折射率分布的组合模型对人眼模型重现实测像差的影响;给出了重现我国人眼实测像差误差最小的晶状体模型.结果显示:晶状体的面型越复杂得到人眼模型的像差与真实人眼的测量像差就越接近;当晶状体采用Zernike面,梯度渐变折射率采用分段函数公式形式时,重现实测像差误差最小.     

基于主观式测量人眼波前像差的眼模型研究

通过主观式光线追踪波前像差测量方法得到用Zernike系数描述的人眼波前像差;在Gullstrand-Le Grand眼模型的基础上,引入用医用角膜地形图仪测量并用高次非球面函数拟合的实际人眼角膜形状数据,又引入角膜、前房及玻璃体厚度等个体化的眼结构参数;在光学建模软件Zemax中用所测Zernike系数建立评价函数,并对用Zernike矢高面描绘的晶状体表面进行优化.由此建立了个体化眼模型,并由此模型中可以计算得到与实际测量的波前像差值完全相同的各项Zernike系数值,从而可用于描述实际人眼的光学特性.     

封面故事

<正>Luneburg透镜,一个经典的渐变折射率分布的球形透镜,具有无像差理想成像和理想聚焦的新奇物性。通过三维空间中渐变折射率介质调控其光传输特性,从而实现传统单一的均匀介质透镜器件所不具有的消像差、大视场的功能,在纳米光子学、集成光学、通信光纤等领域具有重要应用潜力。根据有效介质近似理论,其内部渐变的折射率分布可通过渐变超材料等效为渐变折射率介质来实现,但受现有微纳加工方法的限制,目前已     

双变形镜人眼视网膜高分辨率显微成像系统

如何有效校正随人群起伏很大的人眼像差,提高视网膜高分辨率成像技术的人群适用范围是临床应用面临的最大难题。现有的单一波前校正器无法同时清除高阶和低阶视觉像差。针对人眼高阶像差校正需求,研制成功了169单元3 mm极间距分立式压电变形镜,并与大行程Bimorph变形镜组合,建立了一套双变形镜的人眼视网膜成像系统。系统可实现对离焦小于±4.5 D、散光小于±3.0 D的低阶像差及前8阶Zernike像差的有效校正,极大地提高了系统的人群适用范围和成像质量。以低阶像差大小作为入选标准,进行小样本量人眼视网膜成像实验,获得了近衍射极限的视网膜图像。该系统适用范围明确,便于后续临床应用。     

用特殊眼模型研究人眼像差与色差对视觉的影响

在光轴和视轴不重合的眼球模型中,设计了一种仅消轴向色差(LCA)而保持横向色差(TCA)不变的元件,建立了仅有TCA的眼模型。进而将实测的人眼高阶像差数据沿视轴方向引入眼模型,用以研究色差和高阶像差的相互作用。建立了三款个性化眼球模型,研究了明视觉状态下高阶像差、色差(LCA+TCA)、LCA和TCA对视觉的影响以及它们之间的相互作用。结果表明:对于多数人眼,色差对视觉的影响远大于高阶像差的影响,并且色差的存在进一步抑制了高阶像差的影响。在色差对视觉的影响中,LCA是具有统治地位的因素;对于多数人眼,TCA的影响可以忽略。     

眼波前像差仿真实验研究

像差是衡量光学仪器成像质量的主要指标,在眼科临床波前像差检测对视觉质量评估具有重要作用。本文介绍了波前像差的基本理论,基于Zernike多项式通过仿真分别给出人眼1-4阶共14项波前像差图,可为教学服务,也可为临床医师提供科学参考。     

基于个体眼光学结构的角膜与晶状体的像差补偿

研究角膜对晶状体波前像差的影响对现行的个性化视觉矫正手术有-定的参考价值.运用光学设计软件Zemax,根据个体人眼的角膜地形图、眼内各部分轴向间距和全眼波前像差数据,为22只人眼构建了个体眼光学结构.基于个体眼光学结构和衍射光学理论计算了眼内、外不同位置处的波前,获得了角膜对晶状体波前像差的影响.结果表明,角膜和品状体像差存在补偿和叠加两种关系.大多数眼睛,角膜对晶状体像差有一定补偿作用.总体像散的均方根(RMS)值比品状体像散的RMS值减小0.08～1.48μm,相当于10.1%～77.5%.总体高阶像差的RMS值比晶状体高阶像差的RMS值减小了0.06～0.85 μm,相当于3.8%～79.4%,平均减小了50.7%.其中,球差和彗差的Zernike系数绝对值总体比晶状体分别减小了0.02～0.60μm和0.01～0.39μm,相当于4.3%～98.4%和2.5%～91.4%.     

人眼模型中各折射面对人眼像差的贡献

将计算光学系统各个折射面对系统像差贡献的理论应用于人眼中.用C语言编制光线追迹程序,计算了人眼各个折射面对眼睛像差的贡献及各种像差经过眼睛不同折射面的变化.给出了眼睛中各个折射面对眼睛彗差的贡献,并发现角膜与晶状体对眼睛彗差的贡献有相互补偿的作用.在眼睛中,角膜前表面对人眼像差的贡献最大,晶状体后表面对眼睛像差的贡献次之,这两个折射面比其他两折射面对眼睛像差的贡献大得多.这说明晶状体后表面也是改善人眼像差的参数之一.     

基于均方根误差和相关系数评价人眼像差对视网膜像质的影响

视网膜成像质量的下降会减弱视力等视觉功能,直接影响人们的日常生活。人眼像差是影响其像质的主要因素,为了提高视网膜像质,常用自适应光学矫正人眼像差,以获得接近衍射极限的分辨力或理想像质。矫正波前像差的过程需要以分辨力或像质的评价作为依据。其评价方法大致分为基于瞳孔面和成像面两种,这两种方法主要表征成像系统的分辨力,但不能直观和定量地评价像质。而基于成像面的光学传递函数(OTF)法需要借助曲线面积等才能定量地评价像质,且不同空间频率的像质不同。为此,计算携带人眼像差的OTF,以此模拟人眼成像过程,直观地表征了像质变化。并重新定义均方根误差和相关系数,分析人眼像差对它们的影响,量化地反映各项像差矫正前后的像质变化。     

高频采样下人眼波像差特性研究

为提高自适应光学人眼波像差校正和视网膜成像效果,研究了人眼动态波像差的特性。利用采样频率为300Hz、曝光时间为3ms的哈特曼传感器,搭建波像差探测系统。误差分析和模拟人眼实验表明,该系统对动态波像差的测量误差均方根(RMS)均值仅为0.01λ。人眼波像差探测结果表明,人眼存在150Hz以上的波像差,可能对自适应波像差校正造成影响。这种影响可通过延长探测和成像曝光时间的方法来抑制。为了达到衍射极限,对于稳定盯视状态下的人眼,3ms探测曝光、探测校正周期不超过45ms的自适应系统,其校正残差均方根在λ/14以下;当曝光时间增加到6ms时,该周期可放宽至62ms。研究了倾斜像差的波动对成像的影响,确定了高分辨率人眼眼底成像中,成像曝光时间最长不能超过9ms。上述结果表明,将自适应光学视网膜成像的探测曝光与成像曝光时间均定在6ms左右,可获得更好的校正和成像效果。     

An anatomically accurate eye model with a shell-structure lens

A human eye model based on anatomically accurate eye model previously proposed by Liou, has been transformed into a new eye model, in which laminated structure of the lens is considered. The crystalline lens is presented in the form of hundreds of shells with rotational symmetry, and with constant index within each shell. The refractive index increases from the cortical shell to the inner one, according to the equation proposed by Smith G. et al. The anterior surface of the lens is prolate, whereas the posterior surface of the lens is oblate which is consistent with the anatomical data. A ray tracing procedure has been applied to study the refractive structure of the eye. The optical characters of the model have been studied. The reason that the wings occur on the spherical aberration curve has been given. And we found that the lens with gradient refractive index and lens with shell structure can give same longitudinal spherical aberration results.     

Optical aberrations of the cornea and the crystalline lens

The wave-front aberrations of the anterior corneal surface, the posterior corneal surface and the complete eye have been measured by a corneal topographic system (Orbscan II) and a Hartmann-Shack wave-front sensor. We have calculated the aberrations for both the corneal surfaces with the discrete set of corneal elevation data, and with which to acquire the aberrations of the whole cornea. The aberrations of the crystalline lens are calculated by subtracting the aberrations of the cornea from that of the complete eye. The aberration combination between the anterior and the posterior corneal surface, between the cornea and the crystalline lens is complicated, either compensation or addition. For individual Zernike terms, astigmatism and quatrefoil in the anterior corneal surface are added by the posterior corneal surface, while some other terms show compensation between the two surfaces. And for complete eye, astigmatism and spherical aberrations in the cornea are partially compensated by the crystalline lens, and other terms show addition between the two parts. Individual eye shows different combinations of compensation and addition across different Zernike terms.     

Effect of crystalline lens surfaces and refractive index on image quality by model simulation analysis

The surfaces and refractive index of crystalline lens play an important role in the optical performance of human eye.On the basis of two eye models,which are widely applied at present,the effect of lens surfaces and its refractive index distribution on optical imaging is analyzed with the optical design software ZEMAX (Zemax Development Co.,San Diego,USA).The result shows that good image quality can be provided by the aspheric lens surfaces or (and) the gradient-index (GRIN) distribution.It has great potential in the design of intraocular lens (IOL).The eye models with an intraocular implantation are presented.     

Individual eye model based on wavefront aberration

Based on the widely used Gullstrand-Le Grand eye model, the individual human eye model has been established here, which has individual corneal data, anterior chamber depth and the eyeball depth. Furthermore, the foremost thing is that the wavefront aberration calculated from the individual eye model is equal to the eye's wavefront aberration measured with the Hartmann-shack wavefront sensor. There are four main steps to build the model. Firstly, the corneal topography instrument was used to measure the corneal surfaces and depth. And in order to input cornea into the optical model, high-order aspheric surface-Zernike Fringe Sag surface was chosen to fit the corneal surfaces. Secondly, the Hartmann-shack wavefront sensor, which can offer the Zernike polynomials to describe the wavefront aberration, was built to measure the wavefront aberration of the eye. Thirdly, the eye's axial lengths among every part were measured with A-ultrasonic technology. Then the data were input into the optical design software–ZEMAX and the crystalline lens's shapes were optimized with the aberration as the merit function. The individual eye model, which has the same wavefront aberrations with the real eye, is established.     

Contributions of the cornea and the lens to the aberrations of the human eye

The relative contributions of optical aberrations of the cornea and the crystalline lens to the final image quality of the human eye were studied. The aberrations of the entire eye were obtained from pairs of double-pass retinal images, and the aberrations of the cornea were obtained from videokeratographic data. Third-order spherical aberration and coma were significantly larger for the cornea than for the complete eye, indicating a significant role of the lens in compensating for corneal aberrations. In a second experiment retinal images were recorded in an eye before and after we neutralized the aberrations of the cornea by having the subjects wear swimming goggles filled with saline water, providing a direct estimate of the optical performance of the crystalline lens.     

具有层状晶状体的人眼模型的光学性质

为了更加符合眼睛的解剖学结构,用建立的层状结构晶状体模型代替了Hway-Lan Liou眼模型中的折射率连续变化的晶状体模型。从而建立了新的眼睛模型。在这个新的层状晶状体模型中,最外层前后表面的非球面系数与解剖学数据相符。由于层状结构使光线追迹具有特殊性。因此用C语言编制了光线追迹程序,并对此眼睛模型的光学性质进行了研究。结果表明,晶状体层数较少时,眼睛的球差曲线出现翼状结构．即层状晶状体的引入使眼睛具有多焦性．并对这种现象进行了解释;具有层状结构晶状体的眼睛和具有折射率连续变化的晶状体的眼睛能够给出等价的球差结果。     

Subjective evaluation of intraocular lenses by visual acuity measurement using adaptive optics

We present a new method for subjectively evaluating intraocular lenses (IOLs) without implantation surgery. To illustrate the method, three types of single-piece IOL (equispherical monofocal, rotational symmetric aspheric monofocal, and diffractive bifocal) were assembled into a model eye and evaluated using an ocular adaptive optics system by a single subject. To separate the spherical aberration of the crystalline lens, the subject's corneal topography and wavefront aberrations were measured and modeled. Three levels of Zernike spherical aberration were generated and superposed on the IOLs and the subject's eye. The corrected distance visual acuity was measured by psychophysical visual procedure.