Optical coherence angiography: A review

Abstract

Background: Retinal vascular diseases are one of the most common causes of blindness in the developed world. Optical Coherence Tomography Angiography (OCT-A) is a new noninvasive method that uses several algorithms to detect blood movement. This enables the creation of high-resolution vascular images with contrast depicting motionless tissue.

Methods: This review presents the results of articles relevant to age-related macular degeneration (AMD), diabetic retinopathy (DR), and OCT-A. The OCT-A technique can successfully be used in the diagnosis of neovascularization, retinal vein occlusion (RVO) and retinal artery occlusion (RAO), vessel abnormalities and even anterior segment neovascularization. OCT-A can also be applied to compute data such as vessel density, and flow index in both superficial and deep plexuses.

Results: Many studies have compared fluorescein angiography with OCT-A. Other studies have reported differences in vascular density in AMD patients and have compared them with people having healthy eyes. Although OCT-A offers rapid picture acquisition, high repeatability and resolution, it also has many drawbacks. The most common are: motion artifacts, projections from overlying vessels and limited field of view.An interesting new application is the possibility to assess changes during antivascular endothelial growth factor (anti-VEGF) therapy. Another function of OCT-A is the possible application in the study of choriocapillaries in many fields of ocular pathology.

Conclusion: OCT-A is a new promising method that allows the visualization of the retinal vascular network and the counting of blood flow parameters. This technique provides reliable images useful in clinical routines.

Figure 1

Comparison of wide field FA and 6 mm × 6 mm OCT-A. OCT-A is able to visualize only a small fragment of retina. From right to left top: FA image, Fundus photo with a 6 mm × 6 mm square. Bottom: superficial layer, merged images, deep layer, outer retina, and choriocapilaries. Topcon Triton. Optos California.

Figure 2

From stylistic point of view it should rather be written: Neovascularization at the level of choriocapilaries. Topcon Triton.

Figure 3

Images optic nerve disc in 68-year-old male with DR. Zeiss Cirrus HD 5000.

Figure 4

Comparison of FA and 3 × 3 image in a AMD patients who received 7 Bevacizumab injections. Many spots of anastomosis are visible, dark places near fovea are considered avascular zones. This image was acquired before introduction of motion eye tracking. Topcon Triton.