Detailed Vascular Anatomy of the Human Retina by Projection-Resolved Optical Coherence Tomography Angiography

Abstract

Optical coherence tomography angiography (OCTA) is a noninvasive method of 3D imaging of the retinal and choroidal circulations. However, vascular depth discrimination is limited by superficial vessels projecting flow signal artifact onto deeper layers. The projection-resolved (PR) OCTA algorithm improves depth resolution by removing projection artifact while retaining in-situ flow signal from real blood vessels in deeper layers. This novel technology allowed us to study the normal retinal vasculature in vivo with better depth resolution than previously possible. Our investigation in normal human volunteers revealed the presence of 2 to 4 distinct vascular plexuses in the retina, depending on location relative to the optic disc and fovea. The vascular pattern in these retinal plexuses and interconnecting layers are consistent with previous histologic studies. Based on these data, we propose an improved system of nomenclature and segmentation boundaries for detailed 3-dimensional retinal vascular anatomy by OCTA. This could serve as a basis for future investigation of both normal retinal anatomy, as well as vascular malformations, nonperfusion, and neovascularization.

Angiographic and structural imaging using high axial resolution fiber-based visible-light OCT

“…Although four retinal capillary plexuses in human retina have been reported [52], a projection-resolved algorithm [51,53] has to be applied. By using vis-OCT, projection artifacts of superficial capillary flow were not discerned in the deeper plexuses, presumably because of the combination of stronger reflectance in capillaries located at deeper layers and larger attenuation of the projected superficial flow at visible light wavelengths.…”

“…3(C)). Inspection of the angiographic z-profile showed three distinct retinal plexuses: superficial vascular plexus (SVP), intermediate capillary plexus (ICP) and deep capillary plexus (DCP), resembling the axial vascular distribution of the human retina [51][52][53] and mouse retina [54]. Below Bruch's membrane, the flow signal from the choriocapillaris was detected.…”

Challenges and advantages in wide-field optical coherence tomography angiography imaging of the human retinal and choroidal vasculature at 1.7-MHz A-scan rate

“…Although this OCT image was generated from data with B-scan repeats to enable OCT angiography computations, data acquisition replications are not required in the OCT intensity projection imaging. 37 Capturing OCT intensity data spanning a 30-deg FOV, without exceeding the half-ofthe-1∕e 2 beam spot diameter step, would take only 1 s with 1.7-MHz imaging rate. Imaging a 60-deg FOV would take 3.8 s. However, only limited information about retinal vascular structures is available, e.g., retinal capillaries are not visualized in full depth intensity projections, and can be visualized only in projections from segmented selected retinal layers.…”

“…26,27 In recent years, many OCTA methods have been developed for the imaging of retinal and choroidal vasculature, including: speckle-variance OCTA, 28 phase-variance OCTA, 29 amplitude-decorrelation OCTA (including the split spectrum variant: SSADA), 30 correlation mapping OCA, 31 optical angiography, 32 optical microangiography (OMAG), 33 and power Doppler. 34,35 Unlike classic, fundus photography, or scanning laser ophthalmosocopy (SLO)-based angiography methods, OCTA techniques provide depth information and enable isolation of all vascular retinal 36,37 and selected choroidal 27,[38][39][40][41] layers. However, imaging speed limitations of the OCT techniques require compromises among a set of imaging parameters.…”

Volumetric segmentation of human eye blood vessels based on OCT images

“…In our method we focus on the inner retina vessels located in the ganglion cell layer (GCL) [14]. Fig.…”