Optical coherence tomography angiography: Technical principles and clinical applications in ophthalmology

Abstract

Optical coherence tomography angiography (OCTA) is a functional extension of OCT that provides information on retinal and choroidal circulations without the need for dye injections. With the recent development of high-speed OCT systems and efficient algorithms, OCTA has become clinically feasible. In this review article, we discuss the technical principles of OCTA, including image processing and artifacts, and its clinical applications in ophthalmology. We summarize recent studies which qualitatively or quantitatively assess disease presentation, progression, and/or response to treatment.

Keywords: Choroidal neovascularization; diabetic retinopathy; glaucoma; optic disc; optical coherence tomography angiography; retina.

Figure 1

Image artifacts in a 4.5 mm × 4.5 mm optical coherence tomography angiography of the optic nerve head of a healthy individual. (a) En face optical coherence tomography angiography of superficial vascular complex. The yellow line corresponds to the cross-sectional optical coherence tomography angiography image in panel (b). (c) En face optical coherence tomography angiography of the deep capillary plexus. (d) En face optical coherence tomography angiography of an outer retinal slab extending from the outer boundary of the outer plexiform layer to the Bruch's membrane. A residual line artifact (white arrowheads) from microsaccadic eye motion can still be seen in the en face optical coherence tomography angiography images after registration and processing. Large vessels in the superficial vascular complex can cause two types of artifacts on the deeper layers as seen on the cross-sectional and en face images (b and c): projection artifacts with false positive flow signal (black arrowheads) and shadow artifacts with false negative flow signal (white arrows). Projection artifacts are usually more pronounced at the layers with high optical coherence tomography reflectance signal such as retinal pigmented epithelium (d)

Figure 2

A comparison of optical coherence tomography angiography of the macula (3 mm × 3 mm) of a healthy individual without (a) and with projection-resolved optical coherence tomography angiography (b) projection-resolved optical coherence tomography angiography. Blood vessels of the superficial vascular complex (A1) cast projection artifacts onto the en face images of deeper layers, significantly interfering with the proper visualization of the normal anatomical features of intermediate capillary plexus (A2), deep capillary plexus (A3), as well as the avascular outer retina (A4). (A5) Cross-sectional optical coherence tomography angiogram at the position of the yellow line in (A1). Tail artifacts obstruct the normal avascular boundaries between retinal plexuses and produce false positive flow signal in the normally avascular outer retinal layers. Projection-resolved optical coherence tomography angiography significantly reduced the projection artifacts from the en face (B2–B4) and cross-sectional (B5) angiograms. Normal vascular architecture of the intermediate capillary plexus and deep capillary plexus can be appreciated, with minimal residual projection artifacts in the outer retina and on the cross-sectional image

Figure 3

A case of central serous chorioretinopathy. Early-phase (a) fluorescein angiography image shows minimal leakage, with increasing hyperfluorescence staining in the late-phase (b). However, fluorescein angiography was not able to determine the source of the leakage; whether it was from the central serous chorioretinopathy or secondary choroidal neovascularization. (c) En face 3 mm × 3 mm OCT angiogram corresponding to the green box in Panel A. (d) Cross-sectional optical coherence tomography angiography corresponding to the green line in Panel C. optical coherence tomography angiography revealed abnormal flow signal in the outer retinal slab, beneath the retinal pigmented epithelium, consistent with Type 1 choroidal neovascularization

Figure 4

En face projection-resolved optical coherence tomography angiography images of the parafoveal retinal plexuses of two eyes with mild nonproliferative diabetic retinopathy. Avascular areas in each of the retinal vascular plexuses (a-c, e-g) were detected automatically (blue areas) from the en face projection-resolved optical coherence tomography angiography images, revealing capillary dropout lesions that could not be detected from the combined inner inner retinal angiogram (d and h)

Figure 5

The right eyes of a healthy subject (a) and primary open-angle glaucoma patient (b). Focal capillary dropout in the infratemporal area is apparent in the en face optical coherence tomography angiography of the radial peripapillary capillary plexus of the glaucoma patient (B2, white arrowheads). The optical coherence tomography angiography lesions matched with the visual field defect (B3)