OCT Angiography : Basic Concepts

Abstract

Optical Coherence Tomography Angiography (OCTA) is a non-invasive dye-free imaging technology that creates high resolution depth resolved angiographic images of vascular flow in retina. It is based on the principle of split spectrum amplitude decorrelation angiography algorithm. OCTA gives segmentation of layers as superficial capillary plexus, deep capillary plexus, outer retinal layer, outer retina to choriocapillaris, choriocapillaris layer and choroid layer. OCTA is also useful for visualization of choroidal neovascularization and the monitoring of age-related macular degeneration (AMD) by observing the morphologic changes of choroidal vessels. It is an efficient tool to keep evidence of regression and progression of the disease in follow up cases of AMD patients on anti-VEGF treatment. OCTA plays an important role in the diagnosis of early and advanced changes in diabetic retinopathy (DR). It has the advantage to examine the superficial and deep capillary plexuses separately. The segmentation of layers in OCTA in a case of DR is important in the micro evaluation of the status of the retinal vasculature and for prognostication. Disadvantages of OCTA are that images do not show leakage, dye pooling and tissue staining. It has limited field of view, artifacts, and limited choroidal penetration. OCTA is a useful tool to be used in correlation with structural cross-sectional scans in determining treatment decisions.