人眼视网膜成像自适应光学系统设计

设计一套基于液晶空间光调制器的人眼视网膜成像自适应光学系统,以获得高分辨率视网膜图像,并且使该系统实现体积小,功耗低,成本低等优点.采用夏克-哈特曼探测器和基于硅基板上的液晶器件分别作为波前探测器和波前校正器.系统采用双对准光源以主观方式来使人眼对准,近红外光探测成像以减小对人眼的刺激.使人眼对有限距离对焦,以减小离焦对成像的影响,使该系统既可用于正常眼,又可用于近视眼.用ZEMAX软件对系统进行了模拟分析,认为该系统可获得高于3 μm的视网膜分辨率,该系统设计是合理可行的.     

用于人眼视网膜成像照明的激光消散斑技术研究

以近红外激光(808 nm)作为人眼波前像差探测的信号光和视网膜成像的照明光,液晶空间光调制器(LCOS)作为波前校正器,用哈特曼波前探测器探测人眼像差,构建了人眼像差自适应校正的视网膜成像系统.利用模拟眼分析了激光散斑对相机成像的影响和对哈特曼波前探测器进行像差探测的影响,同时验证了利用旋转散射体的方法消除激光散斑的可行性和有效性;用活体人眼进行了激光消散斑前后照明视网膜进行成像的对比实验,并进一步利用自适应光学技术实现了对人眼像差的动态校正和视网膜细胞的连续成像.校正后,系统波前像差的均方根值小于0.1λ.实验表明激光消散斑后可以同时作为人眼像差探测的信号光和视网膜成像的照明光,从而可以进行连续自适应校正和成像.     

高分辨率开环液晶自适应光学视网膜成像系统

利用液晶空间光调制器和夏克-哈特曼波前探测器作为核心器件搭建了一套开环双光源液晶自适应光学视网膜成像系统。系统采用人眼屈光0D基准设计并使用动态视标定位人眼,提高了人眼在测试时的稳定性,有效降低了由不同人眼个体差异带来的影响。通过补偿镜预补偿,配合微调照明光焦面,使照明光聚焦在眼底视觉细胞层,保证了像差探测精度和成像质量。利用人眼的偏振特性,采用偏振光照明的方式,将系统的能量利用率提高了20%。优化了系统的工作流程,优化后系统连续工作频率可超过20Hz。对4名志愿者进行了实验,均获得了清晰的眼底视网膜细胞图像。     

开环双脉冲液晶自适应光学视网膜成像系统

为了获得高分辨率视网膜图像,利用液晶空间光调制器作为波前校正器建立了一套开环液晶自适应光学视网膜成像系统。与闭环模式相比,采用开环模式后,系统的能量利用率提高了1倍。系统采用双脉冲照明方式,以减少人眼曝光量,保护人眼安全。在照明光学系统中加入了大小视场切换装置使成像视场由之前的0.8°增至1.7°。同时优化了系统的时序控制流程,对人眼像差连续校正的同时快速调节成像相机的前后位置至最佳像面。对于开环模式对动态人眼像差的校正精度进行了测量,实验测得,经开环校正后,残差波面的均方根值约为0.09λ;相应的斯特雷尔(Strehl)比高于0.70,系统分辨率接近光学衍射极限的分辨率。对两名志愿者进行了实验,获得了清晰的眼底视网膜细胞图像。     

液晶自适应光学视网膜校正成像技术研究

为了实现对人眼视网膜的高分辨率成像,解决偏振能量损失、成像视场小和普适性差等问题,对液晶自适应光学技术及其在人眼视网膜成像中的应用进行了研究。通过开环光路的设计方案,避免了闭环液晶自适应系统的偏振光能量损失;在光路中加入可变视场光阑,利用小视场照明进行波前探测、大视场照明进行像差校正和成像的方法扩大了成像视场;使用脉冲光照明的方案减小曝光量;通过偏振光照明提高能量利用率、等效无穷远视标配合补偿镜以及改进后的视标提高盯视稳定性等一系列方法,提高系统普适性。校正后成像的清晰度和对比度获得了明显提高;高分辨率眼底成像视场直径从200μm扩大到500μm;曝光量减小到原来的1/2~1/3;对前期难以获得清晰成像的样本,取得了效果良好的视网膜视觉细胞自适应图像。     

液晶自适应光学视网膜校正成像技术研究

为了实现对人眼视网膜的高分辨率成像,解决偏振能量损失、成像视场小和普适性差等问题,对液晶自适应光学技术及其在人眼视网膜成像中的应用进行了研究。通过开环光路的设计方案,避免了闭环液晶自适应系统的偏振光能量损失;在光路中加入可变视场光阑,利用小视场照明进行波前探测、大视场照明进行像差校正和成像的方法扩大了成像视场;使用脉冲光照明的方案减小曝光量;通过偏振光照明提高能量利用率、等效无穷远视标配合补偿镜以及改进后的视标提高盯视稳定性等一系列方法,提高系统普适性。校正后成像的清晰度和对比度获得了明显提高;高分辨率眼底成像视场直径从200 μm扩大到500 μm;曝光量减小到原来的1/2~1/3;对前期难以获得清晰成像的样本,取得了效果良好的视网膜视觉细胞自适应图像。     

人眼视网膜成像自适应光学系统的初步试验和改进

搭建了一套基于液晶空间光调制器的人眼视网膜成像自适应光学系统,进行了活体人眼视网膜的初步实验.经过系统闭环校正,PV值和RMS值分别从2.293λ降低到0.176 553λ,从0.55129λ降低到0.105 11λ,接近衍射极限的水平.获得了较为清晰的人眼视网膜细胞图像,验证了液晶空间光调制器在人眼视网膜高分辨率自适应成像中应用的可行性,并针对试验中的遇到的激光散斑以及照明控制等问题,对原系统提出了一些改进设计.     

人眼视网膜成像液晶自适应光学系统的优化设计

针对已有的人眼视网膜成像液晶自适应光学系统的不足,提出了新的优化设计方案.新设计的系统能对不同视度下的人眼进行高分辨率成像.新系统还采用了瞳孔监控装置和成像区域快速精确定位装置,并且采用了改进的消杂散光方法,能够使探测准确度和定位准确度得到保证.研究证明,该系统新的设计方案操作方便、灵活,便于推广使用.     

人眼视网膜成像液晶自适应光学系统的优化设计

针对已有的人眼视网膜成像液晶自适应光学系统的不足,提出了新的优化设计方案.新设计的系统能对不同视度下的人眼进行高分辨率成像.新系统还采用了瞳孔监控装置和成像区域快速精确定位装置,并且采用了改进的消杂散光方法,能够使探测准确度和定位准确度得到保证.研究证明,该系统新的设计方案操作方便、灵活,便于推广使用.     

可诱导人眼自动调焦的眼底相机光学系统设计

基于自适应光学设计了一款可诱导人眼自动调焦的眼底相机,包括视度调节系统、照明系统和自适应成像系统。在视度调节系统中,通过设置视标诱导人眼自动调焦,校正人眼初级像差,将人眼残余像差控制在自适应成像系统的校正范围内。在照明系统中,采用轴锥镜组产生环形光照明人眼,消除人眼角膜的强反射光,通过调节轴锥镜之间的距离使环形光束内径连续变化以适应不同的人眼。在自适应成像系统中,使用哈特曼-夏克波前传感器作为波前探测器,使用变形镜作为波前校正器,校正人眼的高阶像差。仿真结果表明,眼底照明均匀度可达95%,自适应成像系统在截止频率76lp/mm处,各视场调制传递函数(MTF)值均大于0.36。系统畸变小于1%,能够对在-6 D~+8 D(D表示屈光度数)之间的人眼眼底清晰成像。     

用于活体人眼视网膜观察的自适应光学成像系统

利用自适应光学技术,研制了两套活体人眼视网膜高分辨力成像系统,在实时校正人眼波前误差的基础上,实现活体人眼视网膜细胞尺度的高分辨力成像。这两套系统分别采用19和37单元小型压电变形反射镜作为波前校正元件,哈特曼-夏克(Hartmann-Shack)波前传感器测量波前误差,用眼底反射的半导体激光作为波前探测的信标。在用计算机控制自适应光学系统实现人眼波前误差校正后,触发闪光灯照明视网膜,用CCD相机记录视网膜的高分辨力图像。校正后的残余波前误差的均方根值已分别小于1／6和1／10波长,相当于视网膜上成像分辨力分别为3．4μm和2．6μm,接近衍射极限。试验表明37单元系统的成像质量更好。     

Retinal axial focusing and multi-layer imaging with a liquid crystal adaptive optics camera

With the help of adaptive optics(AO) technology, cellular level imaging of living human retina can be achieved.Aiming to reduce distressing feelings and to avoid potential drug induced diseases, we attempted to image retina with dilated pupil and froze accommodation without drugs. An optimized liquid crystal adaptive optics camera was adopted for retinal imaging. A novel eye stared system was used for stimulating accommodation and fixating imaging area. Illumination sources and imaging camera kept linkage for focusing and imaging different layers. Four subjects with diverse degree of myopia were imaged. Based on the optical properties of the human eye, the eye stared system reduced the defocus to less than the typical ocular depth of focus. In this way, the illumination light can be projected on certain retina layer precisely.Since that the defocus had been compensated by the eye stared system, the adopted 512 × 512 liquid crystal spatial light modulator(LC-SLM) corrector provided the crucial spatial fidelity to fully compensate high-order aberrations. The Strehl ratio of a subject with-8 diopter myopia was improved to 0.78, which was nearly close to diffraction-limited imaging. By finely adjusting the axial displacement of illumination sources and imaging camera, cone photoreceptors, blood vessels and nerve fiber layer were clearly imaged successfully.     

基于液晶纯相位光调制器的4f系统去噪方法

分析了4f系统的噪声来源,提出使用液晶空间光调制器实时去除系统噪声.通过使用Zemike多项式拟合透镜等光学器件引入的像差,根据液晶纯相位光调制器利用位相共轭波进行静态波面校正的工作原理,提出了一种新的相位校正算法,模拟仿真美国BNS公司反射式256×256纯相位液晶空间光调制器,通过重构并逼近畸变波面,产生相位共轭波...     

Simulated human eye retina adaptive optics imaging system based on a liquid crystal on silicon device

In order to obtain a clear image of the retina of model eye, an adaptive optics system used to correct the wave-front error is introduced in this paper. The spatial light modulator that we use here is a liquid crystal on a silicon device instead of a conversional deformable mirror. A paper with carbon granule is used to simulate the retina of human eye. The pupil size of the model eye is adjustable (3--7mm). A Shack-Hartman wave-front sensor is used to detect the wave-front aberration. With this construction, a value of peak-to-valley is achieved to be 0.086Λ, where Λ is wavelength. The modulation transfer functions before and after corrections are compared. And the resolution of this system after correction (69lp/m) is very close to the diffraction limit resolution. The carbon granule on the white paper which has a size of 4.7μm is seen clearly. The size of the retina cell is between 4 and 10μm. So this system has an ability to image the human eye's retina.     

Retina imaging system with adaptive optics for the eye with or without myopia

An adaptive optics system for the retina imaging is introduced in the paper. It can be applied to the eye with myopia from 0 to 6 diopters without any adjustment of the system. A high-resolution liquid crystal on silicon (LCOS) device is used as the wave-front corrector. The aberration is detected by a Shack-Harmann wave-front sensor (HASO) that has a Root Mean Square (RMS) measurement accuracy of λ/100 (λ = 0.633 μm). And an equivalent scale model eye is constructed with a short focal length lens (∼18 mm) and a diffuse reflection object (paper screen) as the retina. By changing the distance between the paper screen and the lens, we simulate the eye with larger diopters than 5 and the depth of field. The RMS value both before and after correction is obtained by the wave-front sensor. After correction, the system reaches the diffraction-limited resolution approximately 230 cycles/mm at the object space. It is proved that if the myopia is smaller than 6 diopters and the depth of field is between −40 and +50 mm, the system can correct the aberration very well.     

LCOS液晶波前校正器的色散研究

对液晶波前校正器的色散问题进行了研究,测定了250D离焦、250D像散两种像差镜和650 nm、670 nm、710 nm、840~860 nm、835~865 nm、830~870 nm五种滤光片下的色散.结果表明：可见到近红外波段内20~30 nm带宽的光是液晶自适应光学系统的理想光源,可实现系统较大的能量利用率和较小的色散.对于中心波长850 nm的近红外光,当光源的带宽低于30 nm时,LCOS的色散对系统像差影响较小,可以忽略,系统的光能利用率又较大|一旦光源带宽高于40 nm,LCOS的色散会对系统的像差产生明显的影响,使成像分辨率大大降低.     

Adaptive optics fundus camera using a liquid crystal phase modulator

We have developed an adaptive optics (AO) fundus camera to obtain high resolution retinal images of eyes. We use a liquid crystal phase modulator to compensate the aberrations of the eye for better resolution and better contrast in the images. The liquid crystal phase modulator has a wider dynamic range to compensate aberrations than most mechanical deformable mirrors and its linear phase generation makes it easy to follow eye movements. The wavefront aberration was measured in real time with a sampling rate of 10 Hz and the closed loop system was operated at around 2 Hz. We developed software tools to align consecutively obtained images. From our experiments with three eyes, the aberrations of normal eyes were reduced to less than 0.1 μm (RMS) in less than three seconds by the liquid crystal phase modulator. We confirmed that this method was adequate for measuring eyes with large aberrations including keratoconic eyes. Finally, using the liquid crystal phase modulator, high resolution images of retinas could be obtained.