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Takao Hirano, Karntida Chanwimol, Julian Weichsel, Tudor Cosmin Tepelus, Srinivas R. Sadda; Investigation of retinal capillary plexuses in normal eyes using optical coherence tomography angiography axial vessel density analysis. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1511.
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© ARVO (1962-2015); The Authors (2016-present)
Optical coherence tomography angiography (OCTA) provides depth-resolved visualization of the retinal microvasculature. Initial studies have suggested that the 3-dimensional (D) vessel organization may vary by retinal location. To better profile this 3-D structure, we used axial vessel density analysis to evaluate different regions throughout the macula.
In this IRB-approved prospective study we enrolled 22 normal healthy subjects. The right eye of each subject underwent OCTA imaging using a Spectralis OCT2 (version 126.96.36.1990; probabilistic, full-spectrum OCTA). 15°×15°volume scans (768 A-scans × 768 B-scans) centered on the fovea were obtained. Rather than displaying the flow signal on en face OCTA images, flow was assessed axially in 8 regions consisting of superior, temporal, inferior, and nasal areas in both parafoveal (2.5°-3.75°) and perifoveal (6.25°-7.5°) zones. After automated removal of large superficial vessels and projection artifacts, flow signal in each of the eight regions was axially aligned and averaged laterally to generate a vessel density at each axial position. The overall axial profile shape and the appearance and position of separated vessel density peaks in axial depth (indicating distinct vascular layers) were compared among the various regions.
Axial vessel density profiles for all 8 regions are shown in figures below, with the solid and dotted lines showing the mean ± standard deviation, and light grey lines reflecting the individual subjects. In all 8 regions, sharp peaks were noted near the inner and outer boundaries of the inner nuclear layer (INL), corresponding to the intermediate and deep capillary plexuses (ICP and DCP). The superior vascular plexus (SVP), however, varied by region. In all 4 parafoveal regions, the SVP could be resolved into two peaks: a small peak at the nerve fiber layer (NFL) – ganglion cell layer (GCL) junction, and a larger broader peak within the GCL. In the perifoveal region, a single SVP peak was observed. In the nasal, superior, and inferior perifoveal retina the tall SVP peak was shifted towards the internal limiting membrane, reflecting the thick NFL from the arcuate and papillo-macular bundle fibers.
Axial vessel density analysis allows the 3-D organization of the retinal vasculature to be more precisely defined.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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