Recent Advances in Retinal Imaging With Adaptive Optics

A daptive optics imaging systems use active optical elements to compensate for aberrations in the optical path between the camera and the object being imaged. In 1953, Babcock first suggested the use of adaptive optics to improve ground-based astronomy, where the rapidly changing atmosphere can significantly degrade the image quality of a ground-based telescope system. 1 Of course the use of adaptive optics is not limited to astronomical imaging, and in the past few decades there has been a rapid expansion in the applications for which adaptive optics has proven valuable. 2 In vivo medical imaging devices often image tissue through intervening aberrated media, which, like the turbulent atmosphere in the case of ground-based telescope systems, degrades the image. In vitro light microscopy is hampered by specimen-induced aberrations; correcting these aberrations (optically or computationally) with adaptive optics results in increased axial resolution and signal intensity. 3,4 Surgical procedures also stand to benefit from adaptive optics, since the delivery of laser power during retinal and endoscopic surgeries is limited by aberrations induced by the intervening media. Long-range laser communication is made possible by use of adaptive optics to reduce atmospheric aberrations. An especially promising application of adaptive optics is the imaging of the living retina at high resolution. Vision scientists and ophthalmologists have long been interested in imaging cellular structures in the living retina to examine photoreceptor properties in vivo and to more precisely characterize retinal disease. But the human eye suffers from higher order aberrations (induced mainly by the lens and cornea) that degrade reti-nal image quality and limit spatial vision. In 1961, Smirnov was the first to suggest the correction of these higher order aberrations to improve the optical performance of the eye. 5 There was some initial success in recovering the spatial properties of the cone mosaic with speckle interferometry, 6 which largely bypasses these aberrations. That same year, Dreher et al. were the first to use a deformable mirror to improve the quality of retinal images, though they only corrected the astigmatism of the eye (a lower order aberration) based on a subjective refraction. 7 Correcting only lower order Since its first application to retinal imaging nearly a decade ago, adaptive optics has helped researchers make fundamental advances in the understanding of how the human visual system works. The authors review these advances and describe what the future of adaptive optics in retinal imaging may hold in …