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B.C. Chauhan, P.K. Yu, S.J. Cringle, D.–Y.Y. Yu; Confocal Scanning Laser Doppler Flowmetry in the Rat Retina: Origin of Flow Signals and Dependence on Scan Depth . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3575.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the origin of signals from scanning laser Doppler flowmetry (SLDF) and influence of axial scan depth on the measurement of retinal blood flow in rat retina. Methods: SLDF was performed in one retina of 5 adult Sprague Dawley rats using a specially modified Heidelberg Retina Flowmeter. In each animal, a series of axial scans was obtained by changing the laser focus from –2 D to +3 D (in steps of 0.25 D) or from –1 D to +2 D (in steps of 0.125 D) relative to the retinal surface. Fluorescein isothiocyanate (FITC) conjugated dextran angiograms were obtained to identify the angioarchitecture and identify measurement locations in the SLDF flow maps. Axial retinal SLDF flow profiles were obtained in artery, vein, arteriole, venule and capillary using the mean blood flow values in the 2x2, 4x4 and 10x10 pixel measurement windows. Results: SLDF images showed good correspondence with the angiographs and resolution to third order arterioles. Venules draining the deep capillary circulation were also resolved, however, neither the superficial or deep capillary circulations could be visualised in any axial SLDF image of any animal. At deeper locations, flow was imaged from apparently large vessels not identified in the angiograms, suggesting they were choroidal in origin. Arteries and veins had the highest flow values and dependence on axial depth, followed by the arterioles and venules. The peak flow values in the arteries varied from 2000 to 7000 a.u. and in veins from 3500 to 5500 a.u. In all cases, flow measurement values in the artery and vein showed dependence on scan depth with a single peak. The measured flow from capillaries was not dependent on depth and was not different from background levels. Conclusions: SLDF could image flow in larger retinal vessels, but not capillaries. These findings were confirmed in the analysis of axial measurements. Some choroidal vessels were also imaged, even in superficial SLDF flow maps suggesting they may influence measured retinal flow.
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