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John C. Morrison, Elaine C. Johnson, William O. Cepurna, Ruikang K. Wang, Zhongwei Zhi; Effects of IOP on Retinal and Optic Nerve Head (ONH) Blood Flow in Brown Norway Rats Determined by Optical Microangiography (OMAG/OCT). Invest. Ophthalmol. Vis. Sci. 2011;52(14):3495.
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To use optical microangiography/optical coherence tomography (OMAG/OCT) to image and measure the effect of acute IOP elevation on retinal and optic nerve head (ONH) perfusion in the rat eye.
Six adult Brown Norway rats anesthetized with inhalational isoflurane (1.5%) were positioned for OMAG/OCT imaging in custom-made head holders. IOP was elevated by cannulation with a 33 gauge needle connected to a reservoir filled with balanced salt solution. The height of the reservoir was used to elevate IOP, in 10 mm Hg increments, between 10 mm Hg and 100 mm Hg. At each IOP level, 3D data volumes were captured using ultrahigh sensitive (UHS) OMAG/OCT (to determine Doppler angle and blood vessel diameters), followed by repeated B-scans for Doppler OMAG analysis (using 10 frames per second over 20 seconds) to determine blood flow velocity. Velocity and vessel diameter measurements were used to calculate blood flow rate in selected vessels.
Volumetric blood flow reconstructions revealed detailed maps, to the capillary level, of the retinal and ONH microvasculature (see A). Starting from 40 mm Hg, retinal blood flow velocity (+/- SEM) diminished linearly with increasing IOP, and was nearly extinguished at 100 mm Hg, with full recovery after return of IOP to baseline (see graph). Enface images (B and C) of the ONH just posterior to the choriocapillaris revealed capillary patterns of both the ONH (Cap) and the surrounding choroid at both 20 mm Hg (see B) and 60 mm Hg (see C). Velocity measurement in a single section from this region was used to calculate overall capillary velocity within this section, and demonstrated a 25.5% reduction at IOP 60 mm Hg compared to 20 mm Hg. Central retinal artery (CRA), lying inferior to the neural tissue, appears dark in these images since blood is flowing axial to the scanner.
OMAG/OCT can be used to image and measure blood flow in the retina and ONH of the rat eye, and suggests that the effect of acute IOP elevation on blood flow in the ONH may be less than that in the retina.
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