Macular Vascular Imaging and Connectivity Analysis Using High-Resolution Optical Coherence Tomography

Abstract

Purpose To characterize macular blood flow connectivity in vivo using high-resolution optical coherence tomography (HighRes OCT). Methods Cross-sectional, observational study. Dense (6-µm interscan distance) perifoveal HighRes OCT raster scans were performed on healthy participants. To mitigate the limitations of projection-resolved OCT-angiography, flow and structural data were used to observe the vascular structures of the superficial vascular complex (SVC) and the deep vascular complex. Vascular segmentation and rendering were performed using Imaris 9.5 software. Inflow and outflow patterns were classified according to vascular diameter and branching order from superficial arteries and veins, respectively. Results Eight eyes from eight participants were included in this analysis, from which 422 inflow and 459 outflow connections were characterized. Arteries had direct arteriolar connections to the SVC (78%) and to the intermediate capillary plexus (ICP, 22%). Deep capillary plexus (DCP) inflow derived from small-diameter vessels succeeding ICP arterioles. The most prevalent outflow pathways coursed through superficial draining venules (74%). DCP draining venules ordinarily merged with ICP draining venules and drained independently of superficial venules in 21% of cases. The morphology of DCP draining venules in structural HighRes OCT is distinct from other vessels crossing the inner nuclear layer and can be used to identify superficial veins. Conclusions Vascular connectivity analysis supports a hybrid circuitry of blood flow within the human parafoveal macula. Translational Relevance Characterization of parafoveal macular blood flow connectivity in vivo using a precise segmentation of HighRes OCT is consistent with ground-truth microscopy studies and shows a hybrid circuitry.

Deep Capillary Plexus Features in Acute Macular Neuroretinopathy: Novel Insights Based on the Anatomy of Henle Fiber Layer

“…5 , 22 The microcirculation within the human DCP has recently been evaluated using novel high-resolution imaging, showing inflow from intermediate capillary plexus (ICP) small arterioles and outflow through draining venules. 17 , 28 This in series connection hypothesis is supported by animal studies that demonstrated a watershed zone between the retinal and choroidal circulations at the OPL level, 29 and has been used to advocate for a vascular etiology in AMN. 30 , 31 …”

“…The High-Res OCT device allows the acquisition of OCT images with 3 µm axial resolution, which is double that of standard commercial SD-OCT devices and enables precise identification of retinal capillaries and venules. 17 …”

“…Draining venules are small structures with a median vascular diameter of 20 µm with OCT B-scans. 17 Thus, using structural OCT raster scans with an interscan distance greater than 20 µm might have impacted their detection. We also recognize the possibility of incorrect retinal layer segmentation.…”

“…Draining venules were defined using structural OCT as large vessels (diameter ≥15 µm) traversing the inner nuclear layer (INL) with a vertical or oblique orientation angled toward a superficial vessel. 17 The INL/OPL boundary was compared among AMN lesions and other areas to inspect for the absence of DCP capillaries (i.e. round-shaped hyperreflective structures seen with OCT B-scans).…”

Histology of type 3 macular neovascularization and microvascular anomalies in treated age-related macular degeneration: a case study

“…29 An investigational version of Heidelberg Eye Explorer (v. 6.16.100.701, Heidelberg Engineering, Heidelberg, Germany) was used for analysis, processing, and post-processing of data. 3,30 Projection artifact was removed via 3-dimensional vessel-shape estimation and a Gaussian blur filter. 3, 30 Raw (floating point) data were exported as a .VOL file.…”