Design Of Liquid Crystal Adaptive Optical System For Fundus Blood Vessel Imaging

It is significant for diagnose of eye diseases and other diseases such as diabetes and hemal diseases to image retinal blood vessel in high resolution in vivo. Human eyes have all kinds of high order aberrations, so only by adaptive optics (AO) can the resolution of retinal blood vessel be heighten from 20μm to 10μm. It is expected adaptive optical systems based on deformable mirror can achieve this goal. However, adaptive optical systems based on deformable mirror fail in widespread application, due to some weaknesses such as big volume, high cost and small corrective capability. AO based on liquid crystal spatial modulator (LC-SLM) has a great potential in human fundus imaging in high resolution, due to many advantages, such as smaller volume, lower price, lower voltages, large corrective capability, high fidelity and high spatial resolution.Although liquid crystal spatial light modulator also has some disadvantages, such as polarization dependence, dispersion effect, which can reduce the light efficiency. This dissertation firstly researches in the spectrum characters of human eye, calculates the maximum permissible exposure, and then studys on the aberration distribution, the frequence and isoplanatic angle of human eye. Hereby, a single-source close-loop optical system is designed, by which the human eye retinal cells images in high resolution is obtained, but it needs high grade apparatus, has a low signal noise ratio, due to low light efficency. The system is converted a single-source open-loop optical system to enhance light efficiency and imaging quality. However, the above-mentioned optical systems can achieve high-resolution images of cone photoreceptor cells, but they can not achieve high-resolution images of fundus microvessels. By investigating the imaging mechanism, a visible illumination source replaces the infrared one to enhance contrast of blood vessel images. Therefore, a two-source open-loop optical system is design to image retinal microvessels with higher contrast and 500μm field of view which corresponds to isoplanatic angle of human eye. The fixation target is improved to enhance the eye-fixation precision. Some clear retinal microvessels images of 500μm field of view are obtained by the AO system, from which retinal microvessels of 10μm in diameter can be distinguish.This investigation is an innovative work on novel liquid crystal adaptive optics system for human retinal vessel imaging in high resolution. This AO system is distinct in optical design, and fit for widespread application.