An overview of optical coherence tomography angiography and the posterior pole

Abstract

Optical coherence tomography angiography is a relatively new, noninvasive technology that has revolutionized imaging of the retinal and choroidal microvasculature. This technology is based on the detection of movement or changes that represent moving red cells in sequential optical coherence tomography scans. As with other established imaging technologies, it has unique benefits as well as certain disadvantages, which include a limited field of view and vulnerability to imaging artifacts. However, software and hardware improvements are continually evolving to mitigate these limitations. Optical coherence tomography angiography has been used to gain a better understanding of microvascular changes across a spectrum of ocular diseases including diabetic retinopathy, age-related macular degeneration, glaucoma, and retinal vein occlusions. In this article, we review algorithms and techniques commonly utilized in optical coherence tomography angiography systems and compare optical coherence tomography angiography to fluorescein angiography, the current gold standard for imaging the retinal vasculature. In addition, we provide an overview of important optical coherence tomography angiography findings in a variety of ocular diseases. Although the clinical role of this technology is still poorly defined, optical coherence tomography angiography has the potential to become an invaluable tool in the diagnosis and monitoring of vascular pathologies.

Keywords: age-related macular degeneration; diabetic retinopathy; optical coherence tomography angiography; retinal imaging; retinal segmentation; retinal vein occlusion.

Figure 1.

Projection artifact and correction with projection artifact removal (PAR) and projection-resolved OCTA (PR-OCTA). (Top left) Optovue AngioVue OCTA B-scan and (top right) OCTA B-scan with raw angiographic overlay. Note the significant projection artifact visible as long tails of apparent flow projecting from areas of real flow located superficially. (Middle left) default PAR. (Middle right and bottom right) PR-OCTA with increasingly stringent removal of projection artifact (α = 0.2 and 1.0). OCTA: optical coherence tomography angiography.

Figure 2.

Inner retinal segmentation schemes in a healthy eye using the Optovue OCTA system. The top row displays en face images and B-scans from default segmentation of the inner retina into the superficial capillary plexus (SCP) and deep capillary plexus (DCP). The dashed line demarcates the location of the B-scans used in the figure. The bottom row displays en face images and B-scans from inner retinal segmentation into the SCP, middle capillary plexus (MCP), and DCP using manufacturer-recommended custom boundaries. Figures are created with images using default Optovue Projection Artifact Removal (PAR; AngioVue Analytics Version 2017.1.0.151). OCTA: optical coherence tomography angiography.

Figure 3.

Three-layer segmentation in a patient with proliferative diabetic retinopathy. The dashed line denotes location of B-scan used in the figure. Note the enlarged foveal avascular zone (FAZ). Arrows mark vascular abnormalities such as microaneurysms and dilated capillary loops. Figure created with images using default Optovue Projection Artifact Removal (PAR; AngioVue Analytics Version 2017.1.0.151). DCP: deep capillary plexus; MCP: middle capillary plexus; SCP: superficial capillary plexus.

Figure 4.

Default segmentation of an eye with age-related macular degeneration displaying a subclinical choroidal neovascular membrane in the outer retinal slab (OR). Dashed line indicates location of B-scan used in the figure. Note the lack of edema or exudate as well as the overlaid angiographic flow signal within the boundaries of the B-scan. Figures are created with images using default Optovue Projection Artifact Removal (PAR; AngioVue Analytics Version 2017.1.0.151). CC: choriocapillaris; DCP: deep capillary plexus; SCP: superficial capillary plexus.

Figure 5.

Three-layer capillary segmentation of a case of long-standing superotemporal branch retinal vein occlusion (BRVO) of the right eye. The dashed line indicates location of B-scan used in the figure. Enlargement of the foveal avascular zone (FAZ) is visible. Arrows demarcate capillary abnormalities. Note that these abnormalities and capillary dropout appear to be more severe in the deeper capillary layers. Figures are created with images using Optovue Projection Artifact Removal (PAR; AngioVue Analytics Version 2017.1.0.151). DCP: deep capillary plexus; MCP: middle capillary plexus; SCP: superficial capillary plexus.