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Aby Joseph, Andres Guevara-Torres, David R Williams, Jesse B Schallek; Measurement of blood flow in the largest vessels and smallest capillaries in the living mouse retina using an adaptive optics scanning light ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3323. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Blood cell velocities in the mammalian retina range from µm/s to cm/s, depending on vessel size and health. Here we automate blood flow (BF) measurement from the full spectrum of vessels using an adaptive optics scanning light ophthalmoscope (AOSLO).
Anesthetized C57BL/6J mice were imaged with an AOSLO using near infrared light. Vessel lumen diameters were measured in raster mode using sodium fluorescein contrast. Additionally, single blood cells were imaged as they passed through a one dimensional 31 kHz scanning beam (Zhong et al 2008). Images of cell position as a function of time were captured; cells manifest as bright streaks. Streak slope was automatically determined using the Radon transform, which can measure cell velocities up to 1 m/s. BF in each vessel was calculated assuming laminar flow and cylindrically shaped vessels.
Measured inner lumen diameters ranged from 4.5 µm in the capillaries to 53 µm in the largest vessels near the disc. Measured erythrocyte velocities ranged from stopped flow in capillaries to 35 mm/s in large vessels. Temporal variations in velocity, measured in both arterioles and venules, corresponded to heart rates of 202-280 bpm, that matched well with simultaneous measurements with a pulse oximeter.<br /> <br /> The velocity signal was robust in vessels that intersected the scanning beam at less than 40° (45% of vessels), the contrast between erythrocyte streaks being insufficient for remaining vessels. BF in the remaining vessels was estimated by scaling the measured BF in other vessels by the fourth power of the ratio of the widths of each vessel (Poiseuille's Law). Averaging across time, total retinal BF values ranging from 3.76-4.79 µL/min in arterioles and 3.85-4.78 µL/min in venules were calculated.
We quantified BF in the largest vessels and the smallest capillaries in the mouse retina, which has been challenging for other approaches that may lack the necessary spatial and temporal resolution. The rapid rate of acquisition allowed precise measurements of fast blood velocity fluctuations associated with the mouse cardiac cycle, in arterioles, venules and capillaries. This method can provide a complete analysis of hemodynamics throughout retinal circulation, which is important to study ocular diseases that disturb regional and global BF, such as diabetic retinopathy and glaucoma.
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