Adaptive optics scanning light ophthalmoscopy
Unparalleled resolution for in vivo visualization of retinal microvasculature at cellular level
Adaptive optics scanning light ophthalmoscopy (AO SLO) provides unparalleled resolution for in vivo visualization of retinal microvasculature at a cellular level, opening a new window onto the live physiology of vascular disease, said Richard Rosen MD, at the annual meeting of the Association for Research in Vision and Ophthalmology in Seattle, USA.
“The optics of the eye place limits on the resolution achievable with the current imaging devices we use in clinical practice. Using deformable mirrors to correct ocular aberrations, AO SLO improves the lateral resolution by at least an order of magnitude, from 20 microns to 2 microns,” said Dr Rosen, professor of ophthalmology, New York Eye and Ear Infirmary of Mount Sinai, New York, USA,
“Implementation of AO SLO has allowed us to break through the resolution barrier and bring our patients’ individual cells into focus. Further clinical development of AO SLO for studying vascular disease will provide us with new opportunities to understand the impact of therapeutic interventions and will allow us to recognise better solutions for our patients in shorter periods of time.”
Dr Rosen said he likes to refer to the technique as dynamic histopathology, and that is because it reveals details of vessel walls, including deposits on the inner luminal surfaces, structural features of capillaries, such as microaneurysmal dilations, and individual cells, such as pericytes and red blood cells. Using a time-lapse approach, patients can be imaged serially, allowing evaluation of the dynamics of the histopathological changes.
This is a real advantage over conventional pathology slides, which provide only a single frame view of a movie, after the story is over, Dr Rosen commented.
AO SLO imaging is a multimodal technique. It can collect static or dynamic images, using confocal or non-confocal detection schemes, and switch between contrast or non-contrast studies. Each technique emphasises different perspectives of the anatomy, which are complementary.
Dr Rosen illustrated the features of these various functions by presenting a variety of examples. He explained that non-confocal techniques, such as offset pinhole and split detection, enhance vessel wall features and provide the best dynamic sequences of blood flow within the vessels. Motion contrast images enhance the mapping of perfusion networks and display capillary beds at specific depths, while fluorescein-enhanced images display wider expanses of depth and reveal multiple overlying capillary beds simultaneously. By subtracting comparable images from different modalities a better appreciation of the 3-dimensional vascular architecture can be appreciated, Dr Rosen said.