Guidelines on Optical Coherence Tomography Angiography Imaging: 2020 Focused Update

Abstract

Optical coherence tomography angiography (OCTA) has significantly expanded our knowledge of the ocular vasculature. In this review, we provide a discussion of the fundamental principles of OCTA and the application of this imaging modality to study the retinal and choroidal vessels. These guidelines are focused on 2020, and include updates since the 2019 publication. Importantly, we will comment on recent findings on OCTA technology with a special focus on the three-dimensional (3D) OCTA visualization.

Keywords: Choriocapillaris; Choroid; Image analysis; Optical coherence tomography angiography; Retinal vessels; Three-dimensional.

Fig. 1

Optical coherence tomography angiography image of the macula of a healthy subject. The retinal vascularization at the macula includes four different plexuses: the superficial (SCP, first line from top), middle (MCP, second from top), deep (DCP, third from bottom) retinal capillary plexuses, and choriocapillaris (CC, bottom). OCTA images are mainly displayed with en face visualization (images on the right) which is obtained by segmenting the volumetric OCTA scans at specific depths (indicated with the red boundaries). Using this strategy, the flow data within any slab, whose boundaries are red in the left images, are summed or projected into a two-dimensional en face image that can be viewed and studied. These boundaries follow pre-defined layers which can be differentiated on the basis of reflectivity, texture, or other attributes. The layers are (i) the inner limiting membrane (ILM), (ii) the inner border of the inner plexiform layer (IPL), (iii) the outer border of the outer plexiform layer (OPL), and (iv) Bruch’s membrane (BM). This image was captured using the Spectralis HRA + OCT imaging device with OCT Angiography Module (Heidelberg Engineering, Heidelberg, Germany)

Fig. 2

Optical coherence tomography angiography scans (3 × 3 mm) of the macula of a healthy subject (left) and a patient with diabetes (right). Three-dimensional (3D) OCTA images were obtained after thresholding post-processing 3D OCTA data. Voxels above the applied threshold are displayed in red. It is evident that the diabetic case is characterized by a reduced retinal perfusion, as compared with the healthy case

Fig. 3.

3D optical coherence tomography angiography visualization of a macular type 3 neovascularization associated with age-related macular degeneration revealed the presence of two distinct intraretinal lesions with a filiform shape (marked with asterisks), which originate from the deep vascular complex (red arrow) and develop toward the choroid (blue arrow)