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.
Highlights
Optical coherence tomography (OCT) is a non-invasive imaging technology that has the high speed required for 3D volumetric imaging and the high spatial resolution to visualize individual layers in the retina
Corresponding to the radial peripapillary capillaries previously known from histology, but not well visualized by FA11. These observations led to many early studies with Optical coherence tomography angiography (OCTA) in both normal and diseased eyes[24], these analyses have been significantly limited due to flow projection artifact[16,23], which prevented: (1) the ability to separate the intermediate capillary plexus (ICP) from DCP, (2) precise visualization of abnormal neovascularization in avascular areas of the retina, (3) accurate quantification of nonperfusion in normally vascularized areas of the retina, and (4) visualization of the inter-plexus spaces
With conventional OCTA all retinal layers, including the avascular outer retina, appeared to contain flow signal, and no natural boundary could be defined between vascular plexuses
Summary
Optical coherence tomography (OCT) is a non-invasive imaging technology that has the high speed required for 3D volumetric imaging and the high spatial resolution to visualize individual layers in the retina. On en face OCTA, the vascular patterns from more superficial plexuses are duplicated on the deeper layers, making it impossible to obtain a clean image of the deeper vascular plexuses, or to separately visualize the ICP and the DCP, and demonstrating signal in the normally avascular outer retina.
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