High-resolution Adaptive Optics Retinal Microscopic Imaging With Dual Deformable Mirrors

High-resolution retinal imaging technology based on Adaptive Optics(AO) can achieve near diffraction limited retinal images in vivo, which have important value in pathology research, early diagnosis of retinal diseases, monitoring the efficacy of therapies and visual function research. However, due to the characteristics of ocular aberrations and the limited wavefront correcting technology, the AO retinal imaging technology is facing big challenges in clinical application. For example, the imaging system has limited aberration correction ability and the rate of successfully imaging is relatively low. How to effectively correct ocular aberrations which vary fast from person to person and improve the application scope of adaptive optics retinal imaging system is the biggest problem facing in clinical application.In this context, this thesis focuses on high-resolution adaptive optics retinal microscopic imaging technique with dual deformable mirrors(DM). Based on the statistical characteristics of ocular aberrations, the thesis analyses the requirements of AO retinal imaging system for correcting ocular aberrations and presents a correction scheme by using dual DMs. A retinal microscopic imaging system with two DMs is designed and developed in laboratory and experiments of retinal imaging in vivo are conducted on this system. The summarized works mentioned above are detailed as follows:Firstly, the statistical characteristics of ocular aberrations are analysed and the statistical model is built up. After a detailed survey of ocular aberrations, such as its description and characteristics, ocular aberrations data including 676 Chinese eyes are collected and their spatial characteristics are statistical analysed. Furthermore, a ocular aberrations statistical model is developed and this will provide data foundation for following AO system design.Secondly, the requirements of AO retinal imaging system for correcting ocular aberrations are analysed and the correcting scheme by using two DMs are presented. The statistical results of ocular aberrations show that in order to achieve diffration limited retinal imaging, the DM needs to have large stroke and high spatial resolution at the same time. Specifically, the DM needs to have stroke larger than 20 um to correct low order aberrations and it also should have the ability to correct at least up to 8th order Zernike aberrations for compensating high order ocular aberrations. However, It is difficult for a single corrector to compensate both low order and high order ocular aberrations simultaneously. To overcome this problem, we set up the correction scheme by using two DMs and decide to use a large stroke 35-element Bimorph mirror to correct the low order aberrations. In order to meet the correction requirements for high order aberrations, a 145-element discrete piezoelectric DM with 3 millimeters spacing is successfully developed. This DM’s spatial resolution is high enough to correct high order ocular aberrations.Finally, the retinal microscopic imaging system with two DMs is designed and developed in laboratory and experiments of retinal imaging in vivo are conducted on this system. In order to achieve good correction performance and have the system work stably, the matching between wavefront sensor and wavefront correctors is optimized designed. A modified algorithm based on reset of control signals is also proposed to control the two DMs simultaneously. This algorithm can effectively compensate for ocular aberrations and significantly suppress the coupling between two DMs. The imaging system is calibrated and tested after building up, the results show that it can achieve 1.1 times diffraction resolution which is about 2.0um at retina. The system can compensate large low order aberrations up to ±4.5 diopters of defocus and ±3.0 diopters of cylindrical. High order Zernike aberrations up to the 8th order can also be corrected by this system. Both imaging quality and application scope are significantly improved. Taking the size of low order aberrations as inclusion criteria, the system is tested on a small sample group and near diffraction limited retinal images are achieved.