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Abhishek Rege, Karan Raje, Marin Kheng, Antonella Mangraviti, Karansingh Thakur, Betty Tyler, Nitish V Thakor, M Jason Brooke, Ingrid E Zimmer-Galler, Peter L Gehlbach; Noninvasive imaging of retinal blood vessels and blood flow using a custom, non-mydriatic, handheld optical imager designed for use in primary care and telehealth settings. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5975.
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To investigate a custom, non-mydriatic, handheld imaging device designed to non-invasively capture vessel-specific retinal blood flow (RBF).
This investigational device is comprised of a dual-illumination, custom imaging instrument utilizing a combination of laser speckle contrast imaging (LSCI) and indirect ophthalmoscopy. Five adult Wistar rats were anesthetized with a xylazine-ketamine mixture for retinal imaging. The device was held by the operator with the elbow stabilized. Once focusing was achieved in white light illumination, ten fundus photographs were rapidly acquired. The illumination was then changed to red laser illumination and 160 sequential speckle image frames of the same field of view (FOV) were acquired in rapid succession (at 100 frames/second). Images of both eyes were acquired, capturing the optic nerve head and peripheral retina, providing 4 sets of images per animal. The acquired raw speckle images were processed to generate LSCI images, from which vessels were segmented manually (gold standard) and automatically (using custom software) to extract intravascular RBF using LSCI-based estimates of blood velocity and diameter.
LSCI images of major retinal vessels were captured in a ~40° FOV, with the smallest vessel diameters measured at 30 µm. Vessels were well contrasted from the retinal tissue (mean contrast-to-noise ratios of 1.40 and 0.81 in the center and periphery respectively), providing intuitive fundus visualization, complemented with blood flow information (Fig. 1A-B). By analyzing the cross-sections of branching vessels, it was possible to validate the conservation of blood flow at branch points (Fig. 1C). The robustness of measurements is governed by an observed median variability (RMSE) of 5.4% between sequentially obtained intravascular flow-estimates.
This study shows the feasibility of capturing high-resolution images of RBF using a custom, handheld instrument without dye injection or pupil dilation. The functionality of this device exhibits a potential for early detection and improved disease management of various ocular and systemic diseases, while its portability shows promise to significantly impact healthcare delivery in underserved areas through deployment in primary care and telehealth settings.
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