人眼波像差动态特性及微血管像面捕捉的研究

	人眼波像差动态特性及微血管像面捕捉的研究
	郑贤良
学位类型	博士
导师	陈波,宣丽
	2014-07
学位授予单位	中国科学院大学
学位专业	光学工程
摘要	视网膜最细小的血管直径约4～6μm，是人体唯一可以无创观察的微血管；视网膜微血管的高分辨率成像，对高血压、糖尿病等全身性疾病的早期诊断具有重要意义。通过自适应光学技术，可校正人眼像差，将眼底成像设备的分辨率从传统的15~20μm提升至接近衍射极限。然而自适应人眼视网膜成像系统存在校正残差大、图像信噪比低、微血管焦面难以寻找等问题。针对这些问题，本论文对人眼波像差动态特性及视网膜微血管像面捕捉进行了研究。利用共焦小孔滤除神经纤维层的反射干扰光，将共焦小孔直径定在40~50μm，对神经纤维层反射光的滤除率可达到50%~65%。定量提出高于1D近视和远视或0.5D散光的人眼，需在头托处对人眼像差进行预补偿。利用人眼前1D视标减少视调节误差，将离焦像差稳定在0.1μm以内。在此条件下，人眼哈特曼探测器的子孔径数至少为110。人眼波像差存在150Hz（6.7ms）以上的波动，会对自适应校正造成影响，可通过延长探测曝光时间加以抑制。自适应光学成像系统的探测和成像曝光时间均定在6ms左右，校正周期不超过62ms，可将探测校正期间的像差波动控制在λ/14以下。倾斜像差的动态变化会使长曝光视网膜图像产生模糊，需将视网膜成像曝光时间限制在6ms以内。视网膜微血管其主要分布在小凹中心1.5°附近的环围区域，轴向分布在内丛状层和外丛状层；根据测量统计，内丛状层和外丛状层距离视觉细胞层的轴向长度分别是163±17μm和102±7μm。实验所用自适应成像系统在人眼视网膜的景深为36μm，可利用视标将入眼光束聚焦在视觉细胞层，以视觉细胞层为基准，通过3~4次焦面移动实现微血管像面的寻找捕捉。提出使用红外光进行像差探测和微血管寻找、黄绿光成像的自适应视网膜微血管成像系统。通过探测、照明光源的相对离焦和成像相机的预先移动，消除人眼色散对成像的影响。研究了微血管的成像机理，利用灌满墨水的石英纤维和纸屏实验模拟了微血管成像过程。利用消偏成像的方法消除微血管前表面反射光，获得易识别的微血管图像。通过拉东变换抑制噪声、增强微血管的特征识别，可用于视网膜微血管成像焦面的判定。
其他摘要	Characteristics of Wavefront aberrations of human eye and technique on searching for image plane of retinal microvascular were studied in order to improve the correction of human eye wave aberrations and retinal imaging. Calculation value of Fried parameter proved that the least number of sub-apertures of Hartmann wavefront sensor for the human eye was about 110. Detection errors of Hartmann sensor were assigned. Analysis of detection errors result from centroid detecting errors showed that there was a linear correlation. The ratio between them was proportional to the pixel size of CCD in Hartmann sensor and inversely proportional to the focal length of the microlens array. The ratio was 2.219λ/pix when the number of effective sub-apertures was 120. Centroid detecting errors on Gaussian speckle was at most 5*10-3 pix with peak signal of 10000e, corresponding to a detect error less than 0.01λ of RMS. Reconstruction error mainly came from insufficient of modes in reconstruction. Higher order wave error lead to reconstruction error 2 times of itself in RMS, impact of centroid detecting errors modes increases when more modes were used in reconstruction, so the number of modes in reconstruction should be around 35 to 45. Light reflected from NFL affected centroid detection, and could be stopped by aperture conjugate to the IS/OS, when the illumination field diameter on retina was set at 20 ~ 30μm, the reflected light would be stopped by 75% to 55%. Finally, measured the influence of the deep low order aberrations of the human eye in wavefront detection. Defocus should be limited to 1D and astigmatism to 0.5D by compensation of LOA before detection.Dynamics of human eye wave aberrations was measured by a Hartmann sensor with a sample rate of 330Hz. RMS of the error of the entire system for dynamic aberration detection was less than 0.01λ when the error of the Hartmann sensor was less than λ/80. Aberration of the human eye had a higher frequency than 150Hz, which may affect the aberration residuals of AO correction. This effect could be suppressed by increasing the exposure time of detection, and completely eliminated when exposure time was longer than 12ms. Fluctuations of tip and tilt aberration would cause lateral displacement of retinal image from AO systems, so exposure time of imaging should be limited within 9ms. For an fixation eye, AO system would get close to or reach diffraction limit with exposure time of 3ms when the work cycle was less than 45ms. Considering the overall changes in the wave aberration and work cycle of AO system, both exposure times of wave detection and imaging were set to 6ms. Frequency of this adaptive systems was more than 16Hz , corresponding to a correction time of 62ms, RMS of residual aberration less than λ/14.Studied the locations of microvasculature in the retina and confirmed that microvasculature situated about 1.5 ° around fovea in IPL and OPL, which located 163±17μm and 102±7μm from IS/OS. Allowing for the depth of field of human eye, the focal plane was moved 100μm from IS/O, and then stepped 20 ~ 30μm of 3 to 4 times to search for microvasculature. Optical properties of microvascular were analyzed. Polarization characteristics of the human eye was measured. The degree of polarization of reflected light of human eye was about 40% when the eye was illuminated by linearly polarized light. Polarized light imaging was proposed to enhance the utilization rate of light to about 70% and a retinal vascular image with good contrast was achieved. Depolarized light imaging was proposed to decrease the reflection on the front surface of blood vessel. Feature recognitions of microvasculature was studied, Radon transform, which was proposed to process depolarized light images, achieved good noise suppression and recognition.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/41508
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	郑贤良. 人眼波像差动态特性及微血管像面捕捉的研究[D]. 中国科学院大学,2014.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
郑贤良.pdf（2958KB）			开放获取	CC BY-NC-SA	请求全文