Will OCT-A replace FA?
Pr Eric Souied, Dr Ala El Ameen, Dr Irene de Rosa, Dr Alexandra Miere
Fluorescein Angiography (FA) was the historical examination for imaging exudative AMD. Staining and leakage on late frames of the fluorescein angiography examination generate essential images for the diagnosis of exudative AMD. However, intravenous fluorescein injection is known to have various side effects, ranging from nausea to anaphylaxis. Thus, the advent of high resolution optical coherence tomography provided a noninvasive structural imaging technique for patients with CNV. With the emergence of optical coherent tomography (OCT), FA was less and less used, actually sustained for diagnosis of exudative AMD at baseline. Currently, spectral domain optical coherence tomography (SD-OCT) is widely used to assess retinal and choroidal abnormalities in macular disease in general and in AMD in particular because it provides fast, noninvasive information on recurrence, and treatment response. However, because of similar reflectivity, a clear differentiation between vascular and fibrous tissue is difficult. Both conventional angiography and SD-OCT generate two-dimensional images, enabling an indirect visualization of the CNV either by late leakage or the presence of subretinal and intraretinal fluid, but the actual location, morphology, and area of the CNV are difficultly evaluated. By detecting blood flow, optical coherence tomography angiography (OCTA) is a noninvasive, innovative approach in the detection of CNV associated with neovascular AMD. This advanced motion contrast imaging uses amplitude decorrelation technology and high frequency scanning for an in vivo detection of erythrocyte movement (and thus blood flow) inside the retinal and choroidal vasculature. Thus, a precise morphologic analysis of CNV flow is now achievable. Optical coherence tomography angiography findings in Type 1, Type 2, Type 3, and fibrotic CNV associated with neovascular AMD have been described in recent studies. Choroidal neovascularization corresponds almost to a high-flow lesion on OCTA images, with variable sensitivity when compared with multimodal imaging. Although CNV presented with variable morphological features, in some cases, CNV shared a similar microvascular organization. Thus, different patterns were described and named according to specific morphologic features. Recently, some early stages of neovascularization such as quiescent CNV, vascularized drusen or nascent type 3, have been identified with OCT-A imaging. The combination of en-face and B-Scan is needed to identify these entities in early lesions.