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Bang V Bui, Da Zhao, Lin Wang, Brad Fortune, Zheng He; Response of the trilaminar retinal vessel network to intraocular pressure elevation in rat eyes. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4473. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
It is known that inner retinal blood flow is autoregulated to compensate for changes in ocular perfusion pressure (OPP). However, studies have focused on the superficial vessels. Here we test the hypothesis that the superficial, intermediate and deep retinal vascular plexus show different responses to intraocular pressure (IOP) elevation.
Anesthetized (60:5mg/kg ketamine:xylazine) adult Long Evans rats (n=14) were imaged using optical coherence tomography angiography (OCTA) at baseline (IOP 10mmHg) and in follow up mode to examine the vasculature during IOP elevation (10mmHg steps to 110mmHg, each lasting 3 min). We imaged a 20 x 10-degree field starting at one disc diameter from the optic disc margin. Capillary area (i.e. diameter) within a 2D projection image was determined (% region of interest) for three layers based on segmentation of the structural OCT: superficial vascular complex (SVC), intermediate capillary plexus (ICP) and deep capillary plexus (DVP). Increases and decreases in this parameter can be interpreted as functional “vasodilation” and “vasoconstriction”, respectively, of the column of blood flowing above threshold. Comparisons were made between layers (2-way repeated measures ANOVA, layer vs IOP) following normalisation to baseline (% relative to 10mmHg).
Group mean arterial blood pressure at baseline was 125±5 mmHg, thus for the IOPs examined OPP spanned 115±5 to -9±4 mmHg. For OPPs from 115±5 to 77±4 mmHg capillaries within the DCP (9±8%, p<0.05) and ICP (11±10%, p<0.05) showed significant “vasodilation”, whereas those in the SVC showed constriction (-14±6%, p<0.05). For OPPs between 63±4 and 38±4 mmHg, capillary diameter was maintained, by for OPPs below 38mmHg, all layers showed linear attenuation. Significant compression in tissue thickness (retinal nerve fibre, ganglion cell and inner plexiform layers and total retinal thickness) for the same regions were not found until OPP fell below 38mmHg.
These data show that the intermediate and deep vascular plexus in the rat retina have a greater capacity for autoregulation against IOP elevation. This might reflect a redistribution of blood flow to the deeper layers during stress.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Average (n=14, error bars SEM) Relative capillary density in the superficial vascular complex (SVC), intermediate capillary plexus (ICP) and deep capillary plexus (DVP) plotted as a function of ocular perfusion pressure.
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