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Raymond Luval Warner, Alberto De Castro, Lucie Sawides, Ting Luo, Kaitlyn Sapoznik, Stephen A Burns; Measuring flicker-evoked changes in human small vessel retinal blood flow using a dual-beam AOSLO.. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4585.
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© ARVO (1962-2015); The Authors (2016-present)
To use a dual-beam Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO) to measure pulsatile blood flow changes in interconnected regions of the human retina with flicker stimulation.
Five healthy subjects ages 25 to 32 were imaged with the dual-beam AOSLO. A suitable region for imaging connected arterioles, capillaries and venules in the superior parafoveal retina was selected. Vessels were then imaged using two spatially offset channels. The order of imaging of vessel types was randomized and each was measured with 3 repetitions of three 2-minute sessions: (1) No-flicker, (2) Full-Field 10 Hz Flicker, (3) No flicker. 100-frames of 29 Hz video were analyzed (MATLAB™). Red blood cells (RBC) travelling through the targeted vessels were automatically detected (intensity z-score ) across frames. RBC centered regions of interest were averaged over three consecutive frames across the entire video for each vessel and the velocity (mm/s) calcuated from the average displacement of the average RBCs between channels (3.32 ms) (see Figure 2).
RBC velocities were measurable in all subjects. Velocities and pulsatility varied across vessels and individuals. Full-field flicker caused an increase in rbc velocity for the arterioles, venules, and capillaries in all subjects. Average velocities increased 10% in arterioles, 15% for venules, and 13% for the capillaries. The increase was significant (ANOVA) for venules [F(2,12) = 8.92, p= 0.004], capillaries [F(2,12) = 8.92, p = 0.004], and arterioles [F(2,12) = 12.88, p = 0.001].
With the use of the dual-beam AOSLO, we can measure increases in the velocity of vessels <100 µm in the human retina as well as measure diameter changes in single frames to determine flow. Average velocities in parafoveal arteriole, capillary and venules increased in all subjects as well as showed pulsatility for all vessels. The ability to measure how blood flow is controlled in the retinal vasculature is important for understanding how retinal diseases can disrupt this regulation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
A standard deviation map of a subject's parafoveal vessels. Interconnected veins, capillaries, and arterioles (red arrows) are identified and selected for imaging.
A velocity plot for one arteriole in one subject. Frames from the minimum, median, and maximum velocity points are used to measure the diameter of an arteriole as a basis for computing flow.
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