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J. Tam, P. Tiruveedhula, A. Roorda; Leukocyte Dynamics in Parafoveal Capillaries Using AOSLO. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2329.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate leukocyte dynamics in parafoveal retinal capillaries, using noninvasive, in vivo video microscopy in humans.
An adaptive optics scanning laser ophthalmoscope (AOSLO) was used to acquire videos of parafoveal capillaries, showing leukocytes flowing in a single-file manner. Videos were acquired at 840 nm and 60 Hz at overlapping locations near the fovea, for one normal subject with no ocular or systemic conditions. Motion contrast methods were used to enhance visualization of capillaries and leukocytes. We selected capillary segments near the foveal avascular zone (FAZ), where the capillary network was single-layered and planar. Spatiotemporal plots were generated for each capillary segment, and traces on the plots were extracted for analysis. Extracted traces were used to determine leukocyte frequencies; speeds and flow directions were also computed in selected vessels. The computed flow directions were compared to expected flow directions by identifying the arterial and venous ends of capillaries.
The parafoveal capillaries, revealed after motion contrast enhancement on AOSLO videos, were used to guide the selection of capillary segments for spatiotemporal plot analysis. There was considerable variation in the appearance of traces on spatiotemporal plots, but we could identify the traces on the plots that were due to moving leukocytes, which had a characteristic appearance. By comparing leukocyte frequencies between capillaries near the FAZ, we identified four distinct paths of connected capillary segments that accounted for a clear majority of the leukocytes found, which we labeled as leukocyte preferred paths (LPPs). In general, the LPPs were a collection of capillaries that provided the most direct path connecting arteries to veins. For the LPPs, the average leukocyte speed was 1.57 mm/s, and the computed flow directions matched the expected flow directions.
The distribution of leukocytes varied across the parafoveal capillary network. In particular, we confirmed the existence of leukocyte-preferred-paths in retinal capillaries. These methods can be used to investigate leukocyte dynamics in situ.
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