Digital adaptive optics for ocular imaging

A large pupil size (6-8 mm in diameter) leads to a possible high resolution (2-3 micron meter) of retinal imaging due to possible large numerical aperture, if imaging system is perfect. Then, single photoreceptors near the foveal region can be resolved, which provides a powerful tool to study visual processing and diagnose retinal diseases beyond the conventional fundus imagers. However, a host of optical aberrations within a large pupil significantly reduce the effective numerical aperture and thus the resolution. To eliminate the optical aberrations and achieve diffraction limited retinal imaging, hardware based adaptive optics has been developed on wide field fundus imager and scanning laser ophthalmoscope. Hardware based adaptive optics requires a wavefront sensor to measure the aberration, and deformable mirror to correct the aberration. Usually it needs closed-loop feedback to gradually correct the aberration. High cost of the equipments and complexity of operation prevent the wide deployment of hardware based adaptive optics. To eliminate the wavefront sensor and deformable mirror, we developed a digital adaptive optics technology based on the basic principles of holographic method. It can dispense with the expensive hardware pieces and complicated feedback operations required by hardware-based adaptive optics ophthalmic imager. The basic principles of digital adaptive optics has been demonstrated on both wide field imaging and confocal imaging systems. This work promises a compact, cost-effective and easy-to-operate high-resolution ophthalmic imagers.

• C Liu, D Thapa, X Yao , "Digital Adaptive Optics Confocal Microscopy Based on Iterative Retrieval of Optical Aberration from a Guidestar Hologram", Optics Express 25 (7), 8223-8236 (2017).
• C Liu, MK Kim, "Digital Adaptive Optics Line-Scanning Confocal Imaging System", Journal of Biomedical Optics 20 (11), 8223-8236 (2015).
• C Liu, X Yu, MK Kim, "Phase Aberration Correction by Correlation in Digital Holographic Adaptive Optics", Applied Optics 52 (12), 2940-2949 (2013).
• C Liu, X Yu, MK Kim, "Fourier Transform Digital Holographic Adaptive Optics Imaging System", Applied Optics 51 (35), 8449-8454 (2012).
• C Liu, MK Kim, "Digital Holographic Adaptive Optics for Ocular Imaging: Proof of Principle", Optics Letters 36 (14), 2710-2712 (2011).