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Andres Guevara-Torres, Kosha Y Dholakia, Aby Joseph, Jesse B Schallek; Red blood cell flux measured in the same retinal capillaries from seconds to months. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4751.
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© ARVO (1962-2015); The Authors (2016-present)
Recent advances in adaptive optics ophthalmoscopy have enabled exact counts of single red blood cells (RBCs) as they travel within retinal capillaries. Because the approach is non-invasive, it is now possible to reimage the same capillaries from seconds to months providing a unique opportunity to study the functional variables of the capillary network.
6 healthy male C57BL6/J mice (6-12 weeks old) were imaged every two weeks with a custom adaptive optics scanning light ophthalmoscope (AOSLO). We imaged retinal capillaries in the deep stratification at the outer plexiform layer (7-22° from the optic disc). RBCs were imaged with phase contrast enabled by lateral offset pinhole imaging (30 Airy disc diameter offset, 796 nm). RBC flux was measured by placing a 15 kHz line scan across each capillary for 20 s and performing manual RBC counts for 1 s of data.
AOSLO allowed noninvasive imaging of the capillary network at high resolution permitting return to target capillaries at weekly intervals (Fig. 1). We identified 3 key attributes of this network by tracking 55 capillaries in 6 mice:1) The same capillaries measured 18 s apart show low RBC flux variability. The average standard deviation was 5% (ranging from 0.07% to 35%; mean = 157 cells/s). The dominant sources of this modulation were the cardiac cycle and sporadic events like leukocyte passage or capillary shunting.2) The same capillaries measured at two-week intervals show greater variability. RBC flux measured across weeks showed an average standard deviation of 21% (ranging from 0.3% to 89%). Despite greater variability in single vessels, the network flux changed by 6% suggestive of a redistribution of flow.3) RBC flux showed the highest variability when comparing all 55 capillaries across 6 mice. In this case standard deviation was 35% (data compared at 8-week time point). This increase could reveal differences in physiology across mice despite being the same age, gender and strain.
Here we show the first report of repeat measures of retinal capillary flux in mice across time. At the scale of seconds, flux is not constant in the same capillary; modulation arise from heart rate and stochastic shunting. At the level of weeks, individual capillaries show greater changes though network flux is largely maintained. This study in healthy mice provides a baseline from which future studies can track flux changes in retinal disease.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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