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Elena Gofas Salas, Pedro Mecê, Cyril Petit, Kate Grieve, Laurent Mugnier, Jose A. Sahel, Michel Paques, Serge Meimon; Near Infrared Adaptive Optics Flood illumination ophthalmoscope Angiography. Invest. Ophthalmol. Vis. Sci. 2018;59(9):644. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Image-based angiography is a well-adapted technique to characterize vasculature, and has been used in retinal neurovascular studies. Because the microvasculature is of particular interest, being the site of exchange between blood and tissue, a high spatiotemporal resolution is required, hence the use of adaptive optics ophthalmoscopes with a high frame rate. Having a decoupled stimulation/illumination light of the retina makes the use of near infrared (NIR) imaging light desirable, while the need for a large field of view and a lack of distortion implies use of a flood illumination based setup. However, the computation of angiography maps is based on the variation in contrast caused by the absorption of erythrocytes passing through capillaries, and NIR light is not optimal for this absorption. We have therefore developed a new computational method allowing us to realize angiography with an adaptive optics flood illumination ophthalmoscope (AO-FIO) using NIR light.
In vivo retinal imaging was performed on six healthy subjects using the Paris AO-FIO built at Quinze-Vingt National Ophthalmology Hospital. Images of 2°x 4° FOV were acquired at 200 Hz using 860nm light. Contrast of the erythrocytes was enhanced by applying a specific spatiotemporal filter developed for NIR-FIO images.The temporal standard deviation (SD) of each filtered image sequence was then computed.
Spatial filtering was tuned to globule size and temporal filtering selected high frequency image variations. SD maps following this spatiotemporal filtering of microvasculature images on different regions of the retina show the variation of intensity due to the flow of erythrocytes. Capillaries that are barely visible on averaged images therefore appear bright.
Angiography maps of the microvasculature can be computed with AO-FIO using NIR light. We show that thanks to our high pixel rate we can detect erythrocyte flow on capillaries in a large field and at high frequency. The fact that we can achieve this on an AO-FIO using NIR was possible due to the implementation of a processing adapted to the NIR AO-FIO characteristics. The advantages previously mentioned make NIR AO-FIO a relevant technique for stimulation studies. Indeed NIR light implies an improvement in the patient comfort and the possibility of combining this technique in the future with visible light decoupled from the illumination source for neural excitation.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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