For decreasing light loss and diminishing the aberrations of the optical system,an open-loop adaptive optics(AO)system for retinal imaging in vivo is introduced.Taking advantage of the ability of young human eyes to accommodate,there was only one single curved mirror to make the pupil of the eye conjugate with the wavefront corrector and the wavefront sensor.A liquid crystal spatial light modulator(LC-SLM)was adopted as the wavefront corrector because the LC-SLM can be made in a small size to match the sensor.To reduce a pair of lenses or focusing mirrors,the wavefront corrector and sensor are positioned in the noncommon path.The system adopts open-loop control and the high-precision LC-SLM guarantees the effectiveness of the AO system.The designed field of view is 1°on the retina(about 300μm).The image quality was simulated with different mirror surface types,including circular,parabolic,and hyperbolic.A hyperbolic mirror with conic constant−1.07,which is close to−1,could best eliminate the aberrations.Theoretical analysis showed that the optical throughput of this system was at least 22.4%higher than that of a standard transmission AO system.In a practical experiment,a parabolic mirror was positioned in the optical path.Images of the cone photoreceptors and the capillary vessels were obtained successfully.This system simplifies the optical setup in comparison to the commonly used 4F systems while still guaranteeing the effectiveness of AO to correct the ocular aberrations.
Ruixue LiuYue QiXianliang ZhengMingliang XiaLi Xuan
With the help of adaptive optics(AO) technology, cellular level imaging of living human retina can be achieved.Aiming to reduce distressing feelings and to avoid potential drug induced diseases, we attempted to image retina with dilated pupil and froze accommodation without drugs. An optimized liquid crystal adaptive optics camera was adopted for retinal imaging. A novel eye stared system was used for stimulating accommodation and fixating imaging area. Illumination sources and imaging camera kept linkage for focusing and imaging different layers. Four subjects with diverse degree of myopia were imaged. Based on the optical properties of the human eye, the eye stared system reduced the defocus to less than the typical ocular depth of focus. In this way, the illumination light can be projected on certain retina layer precisely.Since that the defocus had been compensated by the eye stared system, the adopted 512 × 512 liquid crystal spatial light modulator(LC-SLM) corrector provided the crucial spatial fidelity to fully compensate high-order aberrations. The Strehl ratio of a subject with-8 diopter myopia was improved to 0.78, which was nearly close to diffraction-limited imaging. By finely adjusting the axial displacement of illumination sources and imaging camera, cone photoreceptors, blood vessels and nerve fiber layer were clearly imaged successfully.
