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Lin An, Murray A Johnstone, Ruikang K Wang; Quantitatively evaluating retinal capillary flow using Optical micro-angiography. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4329.
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To explore the feasibility of an optical micro-angiography (OMAG) technique to evaluate human retinal capillary flow in vivo.
A repeated B-scan scanning pattern was designed to quantify retinal capillary flow. If a red blood cell (RBC) passes through a capillary, the light backscattered from it appears as a bright spot in the OMAG image. If the capillary is sequentially imaged over time, the backscattered light from the RBC’s then appears as intensity peaks over the time. The peak width can represent the time a single RBC passesing through the imaging beam while the peak numbers over the time period depict blood flux.
Fig.1 (a) and (b) are a typical B-scan microstructure image and the corresponding blood flow image. Fig.1 (c) and (d) presents a series of magnified microstructural images and corresponding blood flow images. At the time point 1, Fig.1 (d.i) doesn't show any RBC signal. (d.ii) to (d.v) are the dynamic sequential flow images showing an RBC passing through a capillary. (d.vi) demonstrate that the RBC has left the imaging beam. Assuming the diameters of the RBC and imaging beam are both 5 micros, the velocity is then ~ 400 micros/s. Fig. 2 (a) and (b) are the intensity profiles of two typical capillaries, where the evaluated velocities of RBC are given along with peak signals. By counting the peak numbers, the RBC flux is quantified. The number flux of V1 and V2 are ~ 24/s and ~19/s. We imaged five locations peripheral to fovea. The velocity and flux of the selected capillaries were averaged and compared. The results are demonstrated in Fig.2 (c) and (d), indicating that the RBC velocity and the capillary flux are similar at three retinal layers.
We demonstrate that the OMAG is capable of quantitatively evaluating retinal capillary blood flow. We found that there is no significant difference between RBC velocity and flux passing through capillaries located at different layers peripheral to the fovea.
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