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Serge Meimon, Elena Gofas Salas, Pedro Mecê, Kate Grieve, Jose A. Sahel, Michel Paques; Manipulation of the illumination geometry on Adaptive Optics (AO) Flood Illumination Ophthalmoscope (FIO) for Dark Field imaging of the Retina. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4641.
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Off-axis detection, only implemented on AO-Scanner Laser Ophthamoscope(SLO), led to the detection of previously invisible structures like smaller capillaries blood flow (Chui&Rosen&Burns), retinal pigmented epithelium (Rossi,Scoles) and even Retinal Ganglion Cells (Rossi). Although this modality has an outstanding resolution, it suffers from SLO limitations, namely low pixel rate and distortion. We implemented a structured illumination on a high pixel rate FIO to obtain dark field images in order to detect these structures on a larger field at higher temporal resolution.
In vivo retinal imaging was performed on six healthy subjects, without pupil dilation, using an AO-FIO built at the Paris Quinze-Vingt National Ophthalmology Hospital. Images of 2.4°x2.4° field of view were acquired at 200 Hz using near infrared light. Different illumination geometries were implemented at focal planes conjugated with the imaged retina layer. Noninvasive imaging was performed at different depths in the retina and on three Regions of Interest (ROI): the fovea, the optic nerve head(ONH), and peripheral retina.
Images were obtained in bright and dark field consecutively, in the same location of the retina to enable comparison. Similarly to dark field in SLO, our dark field FIO filters out strong reflective features (such as retinal nerve fibers), thus revealing capillaries, large vessel wall substructure (pericytes, smooth muscle cells) and individual cells with enhanced contrast. 200Hz frame rate videos reveal erythrocyte (red blood cell) and leucocyte flow and trajectory.
Our results show that dark field imaging can be implemented on FIO. The improvement of contrast brought by the use of multiply scattered light combined with the advantages of FIO imaging like wide field, high temporal resolution and the lack of distortion in image acquisition makes this technique a valuable tool for evaluation of the retina. In the next steps, we will optimize the illumination geometry, adapting it for the size of the retinal structure we want to image.
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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