The utility of optical coherence tomography angiography in the management of neovascular age-related macular degeneration – current perspective

Abstract

Optical coherence tomography angiography (OCTA) is a relatively new imaging modality that allows visualization of the retinal and choroidal vasculature. While this has traditionally only been possible through dye-based imaging techniques (fluorescein angiography (FA) and indocyanine green angiography (ICG)), OCTA offers a fast and noninvasive alternative that is readily repeatable and can be used to image the retinal and choroidal vasculature in a single scan without the need for dye injection. Another advantage of OCTA is its ability to produce depthresolved evaluation of the reflectance data from retinal tissue, providing a three-dimensional volume of information. The retinal and choroidal capillary networks are arranged into morphologically distinct layers, from the superficial capillary plexus to the choroid. In the case of neovascular age-related macular degeneration (nAMD), this enables the clinician to determine whether a neovascular network is present, its relative position within the retina/choroid and, with the use of repeated OCTA scans over multiple visits, whether this network is changing. However, there is currently no single standard for acquisition or interpretation of OCTA data. The first commercial OCTA machine (AngioVue, Optovue, Fremont, CA) was introduced in 2014 and was based on spectral domain OCT (SD-OCT). Subsequent OCTA devices have been based on either SD-OCT or swept source OCT (SS-OCT). SD-OCT and SS-OCT are both types of Fourier domain OCT but differ in their light source, wavelength, and photodetector, which results in differences in scanning speeds and resolution of imaging at the various levels within the retina and choroid. The longer wavelength of SS-OCT (~1050 nm, vs ~840 nm for SD-OCT) and reduced sensitivity rolloff enables acquisition of high-resolution OCTA imaging particularly of neovascular networks below the retinal pigment epithelium compared with SD-OCT scanning. The quicker scanning speeds of SS-OCT also allow for a larger area to be imaged. However, different devices utilize different algorithms to process and segment the data acquired, and therefore there are differences in the images produced. Continuous advances in OCTA technology and improvements in the quality of images produced have led to increasing use of OCTA globally for clinical purposes, particularly for the diagnosis and monitoring of macular neovascularization [1]. In this article, we discuss the role of OCTA in nAMD and how it can be of use to clinicians in the diagnosis and management of nAMD.