Bruno Lumbroso, MD; Steven T. Bailey, MD; Yali Jia, PhD; Marco Rispoli, MD; and Maria Cristina Savastano, MD
Optical coherence tomography angiography (OCTA) allows the study and classification of new vessels, highlighting their morphology, flow, and exact localization. Absence of dye staining, leakage, and pooling makes choroidal neovascularization (CNV) visualization easier than on fluorescein angiography. The new vessels may be highlighted with accuracy and assessed both qualitatively and quantitatively. OCTA makes it easy to monitor patients with or without treatment, as the OCTA can be repeated safely without much inconvenience to the patient.1
In this chapter we will first specify CNV features, and then in the following chapter, follow their evolution during treatment.
ASSESSING EXUDATIVE NEOVASCULAR AGE-RELATED MACULAR DEGENERATION CHOROIDAL NEOVASCULARIZATION FEATURES: OCCULT, TYPE 1, CLASSIC TYPE 2, AND TYPE 4 (MIXED)
In the first modern classification made 20 years ago, Gass distinguished visible, or classic new vessels as a network that could clearly be seen on fluorescein angiography, from occult new vessels where fluorescein angiography could show only a slow and progressive dye diffusion or oozing. More recently Jung and Freund have developed a new primarily optical coherence tomography (OCT)-based classification that has been widely adopted (Table 12-1).2
TABLE 12-1. CLASSIFICATION OF NEW VESSELS
| TYPE 1 | 40% underneath the pigmented epithelium |
| TYPE 2 | 9% subretinal |
| TYPE 3 | 34% intraretinal |
| TYPE 4 | 17% mixed |
Reprinted with permission from Jung JJ, Chen CY, Mrejen S, et al. The incidence of neovascular subtypes in newly diagnosed neovascular age-related macular degeneration. Am J Ophthalmol. 2014;158(4):769-779.
In exudative age-related macular degeneration, there are new vessels growing from the choroid and choriocapillaris. They may develop either between Bruch’s membrane and the pigmented epithelium, in which case they are type 1 subepithelial new vessels (called occult until recently), or they may develop in the pre-epithelial subretinal space, in which case they are type 2 new vessels (previously called classic new vessels). In both cases exudation and hemorrhages can be seen. In type 1 the exudation forms a flat pigment epithelium detachment with fibrous and vascular content. In type 2 subretinal fluid and cystoid edema are almost always present. In severe lesions, hemorrhage and alterations of the outer retinal layers can be observed.
Figure 12-1. OCTA of type 1 new vessels. The new vessels have the shape of a Medusa head. From a central feeder vessel some thick branches have a peripheral direction. Type 1 vessels initially always appear under the pigment epithelium, and no flow is observed in the nonvascularized zone. The new vessels may later spread out into the avascular area of the external retina. The neovascular network is often extensive. Flow is high.
Type 3 is described in another chapter.
Type 4, or mixed type, has both type 1 and type 2 new vessels in the same lesion, with a fibrovascular flat pigment epithelial detachment. There is subretinal fluid and cystoid edema, as well as hemorrhages and alterations in the outer retinal layers.
OCTA makes it possible to highlight in a fast, precise, and clear way CNV without the difficulties caused by dye leakage or pooling.3–9 One of the methods of OCTA, currently the most widely used in clinical practice across the world, is the spectrum-amplitude decorrelation angiography (SSADA) technology developed by Huang and Jia.
While fluorescein angiography and indocyanine green (ICG) angiography imaging overlays all the retinal structures in two-dimensional flat images, OCTA makes it possible to separately study the new vessels at different levels of the retina and choroid, and to assess CNV layer by layer and then globally. Recent studies show marked reduction in size and vessel density of the neovascular lesion after intravitreal injection treatment using SSADA OCTA technology.10–12 Using OCTA with the SSADA algorithm it is possible to investigate the vascular architecture and quantify the blood flow within neovascularization at the baseline and during the follow-up after treatment.
It is possible to compare the neovascularization feature by the “change analysis” protocol that is present in some commercially available OCTA machines. This new method allows the detection of the neovascular morphology in the precise retinal area previously analyzed.
The new vessels are assessed and classified on the basis of their morphology, the types of subdivision of their branches, presence or absence of loops, and capillary density. Some peripheral loops may merge at the extremities of radial vessels, while other CNVs have the aspect of a bare tree.
TYPE 1 NEW VESSELS
Type 1 new vessels (formerly called occult) develop under flat pigment epithelium detachments, often between the elevated pigment epithelium and Bruch’s membrane (Figures 12-1, 12-2, 12-3, and 12-4).
Fluorescein Angiography and Indocyanine Green Features
Early leakage hyper-fluorescence increases slowly as there is progressive oozing of the dye. In the very early frames of the ICG, the feeder vessel and its ramifications can be seen. In the late ICG frames, a plaque with margins that are generally sharp can be observed.
Structural Optical Coherence Tomography Features
Very frequently a flat, irregular, or undulated pigment epithelium elevation can be noted. Between the pigment epithelium elevation and Bruch’s membrane, fluid is present. Around the lesion alterations, irregularities and thickening of the ellipsoid zone are seen. OCT shows fibrous layers under the elevated epithelium. There is the danger that the elevated pigment epithelium may tear.
Optical Coherence Tomography Angiography Features
Type 1 vessels initially always appear under the pigment epithelium, and no flow is observed in the nonvascularized zone.13 The new vessels may later spread out into the avascular area of the external retina. The neovascular network is often extensive, and flow is high.
There are new vessels that have been described to have various shapes: Medusa head, coral, bicycle wheel, fan, dead tree, tangled network, filaments, and vascular loops. The morphology leaves no room for uncertainty about diagnosis because features are so different from normal vascularization. The capillaries may be dense or sparse, the vessels may be thin and numerous or, as a result of arterialization and after repeated relapses, they may be thicker, straighter, and rigid in aspect with loss of the thinner capillaries. The loops are mostly seen in the CNV periphery and contribute to the formation of a wheel, fan, Medusa head, or coral-shaped new vessels. They may be frequent, rare, and thin. This vascular complex almost always has a feeder trunk or a bundle of feeder vessels. They present branches that radiate into all directions. Type 1 new vessels generally have a larger surface than type 2 new vessels.
Figure 12-2. OCTA of type 1 new vessels. The new vessels have a rounded shape. Type 1 new vessels generally have a larger surface than type 2 new vessels. From a central feeder vessel some thick branches have a peripheral direction, with anastomoses at the periphery.
Figure 12-3. OCTA of type 1 new vessels. The new vessels have the shape of coral bushes. They have a larger surface than type 2 new vessels. The loops are mainly seen in the periphery. Type 1 vessels initially always appear under the pigment epithelium and no flow is observed in the nonvascularized zone. Flow is high.
Figure 12-4. OCTA of type 1 new vessels. The new vessels have a rounded shape. From a central feeder vessel some thick branches have a peripheral direction, with anastomoses at the periphery. The loops are mainly seen in the periphery.
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