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Andres Guevara-Torres, Aby Joseph, Jesse B Schallek; Population analysis of red blood cell flux in retinal capillaries of mice. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5109.
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© ARVO (1962-2015); The Authors (2016-present)
While blood velocity has been reported with a several ophthalmic techniques, this metric provides no information on the packing density or flow patterns of blood cells in microvessels which may be impacted in disease. In this study, we use an adaptive optics scanning light ophthalmoscope (AOSLO) to visualize single red blood cells (RBCs) and quantify the flux characterize the rheology over a population of capillaries in the healthy mouse retina.
Healthy C57BL/6J mice from 13 to 23 weeks old were anesthetized and imaged with an AOSLO with split detection (Scoles et al. 2014, Guevara-Torres et al. 2015). We used a 796nm light source and no contrast agents were applied. We imaged blood cells in 2 modalities, one with a x-y raster scan at 25Hz and a second modality captured a 15.5 KHz point scan across a capillary of interest where blood cells were imaged as they flowed past the stationary linear scan. Manual segmentation of 12,918 cells allowed the quantification of different aspects of blood cell flow.
The following measurements were obtained:-The average capillary RBC flux measured in the healthy mouse was 156 ± 11 cells/s (mean ± SEM, n=83 vessels in 8 animals)-Ratios of plasma to RBC volume provided measure of mean hematocrit (volumetric fraction of blood cells to whole blood) in the healthy mouse was 0.49 ± 0.06 (n=10 vessels) similar to results reported ex vivo (Jackson Laboratory Mouse Phenome Database)-The confluence of single-file capillaries showed a transition from parachute to disordered arrangement of RBCs indicating microturbulence (Figure 1)-In addition to RBCs, other major blood constituents could be imaged, such as platelets, white blood cells and plasma.
Split detector AOSLO provides a robust way to directly measure single blood cell hemodynamics in the living eye without using exogenous dyes. Blood cell images provide a rich quantifiable dataset in which hematocrit, flux, morphology and rheology can be measured. These measures may provide new evaluation criteria for microvessel blood flow in healthy and diseased eyes as well a basis for understanding metabolite delivery and waste product removal at the capillary level.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure 1: Linear scans across converging capillaries reveal the transition between parachute to disordered RBC arrangement and the interdigitation of these cells.
Figure 2: RBC flux distribution obtained across 83 capillaries in 8 mice
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