Adaptive optics with a micromachined membrane deformable mirror for high resolution retinal imaging

The resolution of conventional retinal imaging technologies is limited by the optics of the human eye. In this dissertation, the aberrations of the eye and their compensation techniques are investigated for the purpose of high-resolution retinal imaging. Both computer modeling and adaptive optics experiments with the novel micromachined membrane deformable mirror (MMDM) device are performed. First, a new aspherical computer eye model is developed to study the aberrations of the eye and their effects on retinal imaging. The aberrations and point-spread functions of the eye are calculated and found to be pupil size dependent and space-variant. The aberration compensation is modeled using customized lens design techniques showing that high-resolution retinal images can be obtained with a dilated pupil through aberration compensation. Due to the space-variant nature and the individual variations of the eye aberrations, adaptive optics techniques are necessary for dynamic aberration compensation. Thus, an experimental adaptive optics retinal imaging system, based on a novel, low-cost, and compact MMDM, is constructed to investigate adaptive optics techniques for eye aberration compensation, where the aberrations are measured using a Hartmann-Shack wavefront sensor. Due to the difficulties in controlling the new MMDM device, a novel control algorithm is developed to generate the desired wavefront for aberration compensation of the eye. The MMDM is characterized and a closed-loop system algorithm is developed for eye aberration compensation in real-time. The system is tested with an artificial eye, showing that it can effectively compensate for low-order and to a certain extent for high-order aberrations of the eye. A diffraction-limited resolution is achieved when the aberrations are within the working range of the MMDM. Aberration compensation and retinal imaging experiments are also performed with real eyes, showing an improved imaging resolution. In addition, a preliminary investigation into a complementary adaptive optics approach of using image deconvolution techniques is also conducted to improve retinal image resolution when the aberrations of the eye can not be completely compensated for by the MMDM. Future research can be conducted based on this dissertation to obtain high-resolution 3-D retinal imaging.