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Bingyao Tan, Erik Mason, Ben MacLellan, Kostadinka K Bizheva; The Effect of Elevated Intraocular Pressure on the Rat Retina’s Physiological and Blood Flow Response to Flicker Stimulation. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4864.
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© ARVO (1962-2015); The Authors (2016-present)
To measure in-vivo changes to the functional and blood flow response of the rat retina to flicker stimulation, induced by acute elevation of the intraocular pressure.
A group of eleven-week old male Brown Norway (n=6) rats were dark-adapted for at least 12 hours before ketamine/xylazine anesthesia. The IOP was raised acutely and unilaterally to 45 mmHg by placing a vascular loop anterior to the equator of the eye. A white light flicker (2 s duration, 10 Hz) was applied to stimulate the retina before and during placement of the vascular loop, as well as about 10 min after removal of the loop. Doppler optical coherence tomography (DOCT) was used to measure stimulus-induced changes in the total retinal blood flow (RBF) by integrating over all blood vessels around the retinal optic nerve head. ERG recordings were acquired simultaneously with the DOCT data acquisition. DOCT and ERG data were acquired before, during and after application of the visual stimulus. Five DOCT and ERG recordings were acquired at each experimental time point (before during and after IOP elevation).
Under normal IOP, the total RBF was 5.6 ± 1.9 µL/min and the blood vessel size (BVS) was 70.2 ± 7.1 µm (average over all recordings from all animals). During IOP elevation, the total RBF was significantly lower (3.8 ± 1.2 µL/min, p=0.024) and the BVS was significantly smaller (56.0 ± 4.2 µm, p<0.01). Both the total RBF and BVS returned to normal values within ~10 min from removal of the vascular loop (normal IOP level). The flicker-induced RBF change measured under normal IOP (6.0% ± 3.3%) was reduced significantly to 0.1% ± 0.3% (p < 0.01) during the IOP elevation, and recovered to 5.9% ± 1.7% after the IOP returned to normal after removal of the vascular loop. The magnitude of the second harmonic component (SHC) of the recorded flicker ERG traces decreased to 55% from its baseline value during the IOP elevation (p<0.01), and remained significantly smaller than baseline after IOP normalization (p<0.01).There was no significant change to the first order harmonic components of the flicker ERG.
Results from this study suggest that both the retinal physiology and blood perfusion are altered during acute IOP elevation, and establish a correlation between the functional and blood flow changes.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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