Segmentation of the Four-Layered Retinal Vasculature Using High-Resolution Optical Coherence Tomography Angiography Reveals the Microcirculation Unit

Abstract

Citation: Muraoka Y, Uji A, Ishikura M, Iida Y, Ooto S, Tsujikawa A. Segmentation of the four-layered retinal vasculature using high-resolution optical coherence tomography angiography reveals the microcirculation unit. Invest Ophthalmol Vis Sci. 2018;59:5847-5853. https://doi.org/ 10.1167/iovs.18-25301 PURPOSE. To differentiate the four layers of the retinal vessel network in the human macula and examine their morphologic features using high-resolution optical coherence tomography angiography (HR-OCTA).METHODS. Macular areas measuring 464 3 464 pixels of 10 right eyes of 10 healthy subjects without ocular disease were scanned 10 times using a HR-OCTA device. Averaged OCTA images were created. Based on clear decorrelation signals, four vascular slabs were segmented, comprising one each in the retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), and top and bottom of the inner nuclear layer (INL). Qualitative features and quantitative measurements in each slab were compared with those in conventionally segmented slabs.RESULTS. HR-OCTA isolated four layers of vascular plexuses in the macula that followed the corresponding anatomic layers. Segmentations for the RNFL revealed that radial peripapillary capillaries (RPCs) extended to the central macular area. The RPCs followed relatively straight and long paths, with few apparent feed points and anastomoses. The GCL slab enhanced visualization of the capillary-free zones around the arteries and arterioles and helped to differentiate arterial and venous systems. The arterioles and venules were linked by capillaries that were arranged in a mesh-like fashion, with multiple arteriolar feed points and anastomoses. Vascular plexuses in the top and bottom of the INL consisted of capillaries in a vortex arrangement. The center of these vortex arrangements was consistent with the venules in the GCL.CONCLUSIONS. HR-OCTA can differentiate the four layers of vascular plexuses in the human macula and elucidate their angiographic features.

Accuracy and Reliability in Differentiating Retinal Arteries and Veins Using Widefield En Face OCT Angiography

“…In recent studies, Balaratnasingam et al22 histologically showed the capillary-free zone (approximately 30–50 μm in diameter) along parafoveal retinal arteries and also demonstrated that four different OCTA devices could clearly visualize this zone along retinal arteries but not veins. Muraoka et al23 also demonstrated that averaged high-resolution OCTA images enhanced visualization of the capillary-free zones around the arteries. These findings suggest one means by which arteries can be directly identified on OCTA alone.…”

A Study of the Association Between Retinal Vessel Geometry and Optical Coherence Tomography Angiography Metrics in Diabetic Retinopathy

“…The recently developed high-resolution OCTA can segment additional vascular layers and visualize the pre-capillary arteriole, which is known to play an important role in retinal vascular function and autoregulation. 24 A further study using high-resolution OCTA could contribute to expanding our understanding of the pathophysiology in DR.…”

Pearls and Pitfalls of Optical Coherence Tomography Angiography Imaging: A Review

“…Since the introduction of OCTA, a number of models have been proposed regarding connections among the retinal vascular plexuses [29][30][31][32].…”

“…The small capillaries arise from SCP arterioles and drain into SCP venules. The GCL slab enhances visualization of the capillary-free zones around the arteries and arterioles and helps differentiate arterial and venous systems [32]. Using OCTA, SCP arterioles were demonstrated to be located more superficially than SCP venules [30].…”

“…The retinal nerve fiber layer contains the radial peripapillary capillary network to supply oxygen and metabolites to the optic nerve axons. The RPCP is composed of long, straight vessels with few apparent feed points and anastomoses [32]. These capillaries arise from peripapillary retinal arterioles, extend radially from the optic disc in parallel with the nerve fiber axons, farthest along the temporal arcades [41].…”