Research On Technology Of Wavefront Reconstruction For Human Retina Cell Imaging

As an emerging technology which is growing rapidly in recent years, adaptive optics has been extensively used in the fields of astronomical observations and laser-guide-star (LGS). With the development of micromachining technology, adaptive optics system of micro-miniature and low cost appears. The application of this technology extended from areas of satellite-borne camera, telescope system and laser nuclear fusion to the civilian projects, such as Ophthalmic Medical items. One of the hotspots among is the imaging system of retina cell based on the measurement and correction of wavefront aberration. In this paper, the measurement and correction of wavefront aberration, based on adaptive optics, has been researched systematically as the key technology. A high-precision wavefront aberration reconstruction method which has successfully applied in the human retina cells imaging system was found, and it effectively improved the measurement and aberration correction performance of the adaptive optics system. Real-time measurement and aberration correction in human eye was realized and got a clear picture of the retinal cells.The content of this paper mainly includes:1. It described the physiology structure of human retina, analyzed the principle of imaging of human eyes and the influence of imaging quality through the mathematical model of wavefront aberration.2. Based on the research of principle of detection and theoretical model of Hartmann-Shark wavefront sensor, it analyzed the structure, operation and assembly error which has influences on detection accuracy. A new self-reference method is given in this paper to calibrate the parameter of Hartmann-Shark wavefront sensor with point light source .3. The key techniques are analyzed in depth, include: the maximum permissible exposure calculation of laser used to measure wavefront aberration of human eyes, formation principle of laser speckle and the technique for reducing speckle by using rotating diffuser, the influence of mode selection on reconstructing wavefront aberration of human eyes.4. A new adaptive method is given to estimate the centroid of images after analyzing spot pattern characteristics of human eye aberration. This method is based on the morphological filter, dynamic tracing of spot window, and iterative approximation algorithm. The experimental results show that the method is with strong anti-noise ability, and obviously improves the spot recognition rate and centroid detection accuracy, which effectively extends the applicability of Hartmann-Shack wavefront sensor.5. Based on micromachined membrane deformable mirror(MMDM), a miniaturized and low-cost human retina cell imaging system was first built in China, including a set of optical platform based on adaptive optical system and a software control system accompanying. The functions of software control system consist aberration measurement, calibration of influence function of deformable mirror, closed-loop feed back correction and retina cell imaging. In addition, the preferences were optimized in aberration correction in order to match the different size of pupil, which makes it possible to operate with dilation-free.6. We tested the ability of aberration measurement and correction about the adaptive optics system, and do the experiments of aberration measurement and correction with model eyes, rabbit eyes and pig retina. Human eyes have been tested finally after analysis and conclusion. Clear retina cell images were acquired successfully.