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DA Nelson, R Ofri, I Vanzetta, A Grinvald; Dynamics and Regulation of Blood Flow Rate in Cat and Human Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):843.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Autoregulation of total retinal blood flow volume after intraocular pressure (IOP) elevation is known to occur, but little about its effects on flow in smaller vessels has been described. The Retinal Functional Imager (RFI) (Optical Imaging, Inc.), directly images flow in these vessels. Using it, normal and elevated IOP retinal flow rates were measured in cat. For comparison, normal IOP flow rates were measured in human. Methods: The RFI measures flow by obtaining and analyzing sequential retinal images. Cat imaging parameters : 1-2s recording at 100 Hz; low-intensity illumination possible due to cat’s reflective tapetum. Human imaging parameters: 100ms at 50 Hz.; high-intensity flashes were used, well within ANSI exposure standard limits. Both macula and optic disk were imaged. Surgical procedures: Cats were anaesthetized by a ketamine/diazepan continuous IV drip. Cat IOP was acutely elevated up to 50 mm Hg by cannulation to an elevated saline bag, for < 90 min. Results: Cat normal IOP: blood flow rate was up to 2 mm/s in the capillary bed. It ranged up to 30 mm/s in identified retinal blood vessels. Cat elevated IOP: In main and secondary vessels, flow rate dropped up to 30% two minutes after large-step IOP elevation. This decrease appeared as a transient, consistent with auto regulation; flow rate returned to baseline values after five minutes, even though IOP remained elevated. In capillaries, blood flow rate quickly decreased by approximately 10% per each 10 mm Hg pressure increase; however, in most of the capillaries it did not recover back to normal even after 30 minutes. Human normal IOP: Flow rates in most of the smallest identifiable vessels were < 5 mm/sec; small venous vessels in particular showed a mean flow rate of 3 +/- 1 mm/s. Conclusion: Rates of flow in large and small retinal blood vessels are differentially affected by the autoregulatory mechanisms that maintain overall perfusion volume. RFI-measurable small blood vessels in human have flow rates similar to the range of flow rates most sensitive to sustained reduction in cat, suggesting that measurements of small-vessel flow rates in human would reflect changes in retinal perfusion associated with glaucoma, diabetic retinopathy and other retinal diseases.
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