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Nimesh Bhikhu Patel; Sequential OCTA scans have greater signal variability around venules.. Invest. Ophthalmol. Vis. Sci. 2022;63(7):2959 – F0113.
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© ARVO (1962-2015); The Authors (2016-present)
Optical coherence tomography angiography (OCTA) slab projections represent vasculature in which blood flow meets or exceeds threshold. Sequential OCTA scans have regional variability, and averaging slabs improves visualization of capillaries. We hypothesize that some of the regional variability reflects on blood flow physiology. The purpose of this study was to quantify regional OCTA signal variability from sequential scans for vessels in the superficial vascular complex.
Data were collected from seven non-human primates with no ocular pathology. Prior to imaging, animals were sedated with ketamine and xylazine, and pupils dilated with 1% tropicamide. Six sequential, high speed 384x384 (15°x15°) OCTA raster scans (Spectralis OCT2), centered on the macula, were acquired from one eye of each animal. Scan volumes were imported into Matlab, registered in 3D, and the thresholded signal between the inner limiting membrane and inner plexiform layer isolated. Variability was quantified as the standard deviation of the theresholded signal using a 20x20 A-scan sliding window for identical regions of the six scans. Major vasculature was manually traced on the averaged 2D slab projection, and a 16 pixel dilated region used to compute the average variability surrounding each vessel. Arterioles were identified based on the capillary free zone.
All animals had healthy eyes at the time of imaging, and the mean ganglion cell complex thickness was 103±5.3µm. The average superficial vascular complex slab density was 40.6±3.5%, and volumetric vascular density was 6.9±0.7%. A total of 47 arterioles and 46 venules were identified and traced. The mean standard deviation of OCTA signal was greater around venules (1.11x10-3) compared to arterioles (9.25x10-4, p<0.01).
Averaging OCTA scans improves visualization of capillaries. The variability in OCTA signal is greatest around venules, which is likely a reflection of regional differences in blood flow. In addition to vessel density, OCTA signal variability from sequential scans may provide important physiological information when assessing ocular health.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.
Average slab projection from six sequential scans in a healthy eye. The panel on the right illustrates the OCTA signal variability map.
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