Blood flow is a useful indicator of the metabolic state of the retina. However, accurate measurement of retinal blood flow is difficult to achieve in practice. Most existing optical techniques used for measuring blood flow require complex assumptions and calculations. We describe here a simple and direct method for calculating absolute blood flow in vessels of all sizes in the rat retina. The method relies on ultrafast confocal line scans to track the passage of fluorescently labeled red blood cells (fRBCs). The accuracy of the blood flow measurements was verified by (1) comparing blood flow calculated independently using either flux or velocity combined with diameter measurements, (2) measuring total retinal blood flow in arterioles and venules, (3) measuring blood flow at vessel branch points, and (4) measuring changes in blood flow in response to hyperoxic and hypercapnic challenge. Confocal line scans oriented parallel and diagonal to vessels were used to compute fRBC velocity and to examine velocity profiles across the width of vessels. We demonstrate that these methods provide accurate measures of absolute blood flow and velocity in retinal vessels of all sizes.
Bibliographical noteFunding Information:
Received January 16, 2015; accepted April 21, 2015; First published April 29, 2015. 1The authors declare no competing financial interests. 2Author Contributions: T.E.K. and E.A.N. designed the research; T.E.K. performed research; T.E.K. analyzed data; T.E.K. and E.A.N. wrote the paper. 3This work was supported by National Institutes of Health Grant EY-004077 and Fondation Leducq. Acknowledgements: The authors thank Michael Burian for his invaluable technical assistance; and Kyle Biesecker, Michael Burian, Joanna Kur, and Anja Srienc for their helpful discussions and for reviewing the manuscript.
© 2015 Kornfield and Newman.
- Blood flow
- Red blood cell velocity