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OCT Angiography Imaging of Macular Neovascularization in AMD

Home / Retina and Vitreous / Age-Related Macular Degeneration and other Causes of Choroidal Neovascularizaton

Authors: Jeremy Liu, MS4, University of Hawaii, John A. Burns School of Medicine; Mengxi Shen, MD, Bascom Palmer Eye Institute; Philip J. Rosenfeld MD, PhD, Bascom Palmer Eye Institute

Date: 6/28/22

Keywords/Main Subjects: Age-related macular degeneration, Macular neovascularization, OCT angiography, En face OCT imaging

Overview

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss and legal blindness among the elderly worldwide.1-3 Macular neovascularization (MNV) is the hallmark of neovascular AMD and is defined by abnormal growth of new vessels that invade the outer retina, subretinal space, or sub-retinal pigment epithelium (RPE) space. The exudative stage of neovascular AMD (also known as wet AMD) manifests when these new blood vessels leak, resulting in fluid accumulation and/or hemorrhage in the macula, which causes distortion and deterioration in vision. Without treatment, exudative MNV will result in fibrosis with severe central vision loss.4,5

Pathophysiology

The mechanisms causing AMD are complex and multifactorial. They include genetic susceptibility and environmental factors that affect aging-associated dysfunction of normal retinal homeostasis, impaired lipid metabolism, immune activation and progression to chronic inflammation, oxidative stress, and extracellular matrix dysfunction.4 Even though there have been major advances in our understanding of AMD, the exact relationship between the different pathologic features is largely unknown.

Studies have shown that alterations in the choriocapillaris, Bruch’s membrane (BM), and RPE impact the transport of cellular by-products out of the macula in AMD. These events can lead to hypoxia that promotes vascular endothelial growth factor (VEGF) being released by the RPE and inflammatory cells. Subsequently, a cascade of angiogenic responses is initiated at the level of the choroidal endothelium including the development of MNV.4-6

Histological Classification of MNV

Clinical Findings

In the presence of MNV, the patient usually experiences an acute decrease in visual acuity as well as visual distortion (ie, metamorphopsia), and central visual field defects (ie, scotomas) over several days. The retinal examination will show macular neovascular lesions associated with subretinal fluid, retinal pigment epithelial detachments (PEDs), cystoid macular edema, exudation, and/or hemorrhage.5

OCT Angiography

En face OCT angiography (OCTA) is a new technology that can image the retinal and choroidal microvasculature without the intravenous infusion of angiographic dyes.12-14 It uses motion contrast that arises from the reflectivity of moving red blood cells by comparing the decorrelation signal between B-scans to depict vessels through different areas of the eye with the retinal and choroidal circulations being the most highly studied. This method relies on the principle that only circulating red blood cells within the retinal vasculature are moving in the retina. OCTA is available on both spectral domain (SD-OCT) and swept source OCT (SS-OCT) instruments. To visualize the MNV on the OCTA, different boundary slabs or segmentations are used depending on the location of the MNV in the retina.4,5,14

The main advantages of OCTA are the shorter acquisition time and its non-invasiveness. In contrast, fluorescein and indocyanine-green angiography require an injectable dye which takes time and may be associated with systemic adverse effects. One of the main limitations of OCTA is the inability to image leakage of vessels. In addition, artifact caused by motion, media opacities, and segmentation errors can reduce image quality.15

OCTA Imaging of MNV

Figure 1. Type 1 macular neovascularization (MNV): 6 mm x 6 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a left eye with type 1 MNV.

Figure 1. Type 1 macular neovascularization (MNV): 6 mm x 6 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a left eye with type 1 MNV. (A) En face SS-OCTA flow image of the type 1 MNV (yellow arrow). The bright blue solid line indicates the location of the B-scans below. (B) En face structural image from the same slab used in (A). The neovascular lesion usually appears dark due to the scattering of light caused by the blood flow within the neovascularization. (C) Horizontal B-scan with flow and segmentation boundaries corresponding to the en face images in (A) and (B). The red color represents flow above the retinal pigment epithelium (RPE) and the green color represents flow below the RPE. Segmentation boundaries are depicted by dotted yellow lines with the upper boundary following the RPE and the lower boundary following Bruch’s membrane (BM). (D) Horizontal B-scan without flow or segmentation lines showing RPE elevation or a double layer sign (DLS) at the location of the type 1 MNV (yellow arrow).

 

Figure 2. Polypoidal choroidal vasculopathy (PCV): 12 mm x 12 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a right eye with PCV.

Figure 2. Polypoidal choroidal vasculopathy (PCV): 12 mm x 12 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a right eye with PCV. (A) En face SS-OCTA flow image of the polyps (yellow arrow) and branching vascular networks (BVNs) (blue arrow). The bright blue solid line indicates the location of the B-scans below. (B) En face structural image from the same slab used in (A). (C) Horizontal B-scan with flow and segmentation boundaries corresponding to the en face images in (A) and (B). The red color represents flow above the retinal pigment epithelium (RPE) and the green color represents flow below the RPE. Segmentation boundaries are depicted by dotted yellow lines with the upper boundary following the RPE and the lower boundary following Bruch’s membrane (BM). (D) Horizontal B-scan without flow or segmentation lines showing a dome-shaped elevation of the RPE at the location of a polyp (yellow arrow) that is connected to the edge of a shallow elevation of the RPE that represents the BVNs (blue arrow). In addition, subretinal and intraretinal fluid is present near the polyp and BVNs.

 Figure 3. Type 2 macular neovascularization (MNV): 6 mm x 6 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a right eye with type 2 MNV.

Figure 3. Type 2 macular neovascularization (MNV): 6 mm x 6 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a right eye with type 2 MNV. (A) En face SS-OCTA flow image of the type 2 MNV (yellow arrow). The bright blue solid line indicates the location of the B-scans below. (B) En face structural image from the same slab used in (A). (C) Horizontal B-scan with flow and segmentation boundaries corresponding to the en face images in (A) and (B). The red color represents flow above the retinal pigment epithelium (RPE) and the green color represents flow below the RPE. Segmentation boundaries are depicted by dotted yellow lines with the upper boundary following the outer plexiform layer (OPL) and the lower boundary following the RPE. (D) Horizontal B-scan without flow or segmentation lines showing intraretinal fluid and subretinal hyperreflective material (SRHM) corresponding to the type 2 MNV (yellow arrow).

Figure 4. Type 3 macular neovascularization (MNV): 6 mm x 6 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a right eye with type 3 MNV.

Figure 4. Type 3 macular neovascularization (MNV): 6 mm x 6 mm swept-source optical coherence tomography angiography (SS-OCTA) scan of a right eye with type 3 MNV. (A) En face SS-OCTA flow image of the type 3 MNV (yellow arrow). The bright blue solid line indicates the location of the B-scans below. (B) En face structural image from the same slab used in (A). (C) Horizontal B-scan with flow and segmentation boundaries corresponding to the en face images in (A) and (B). The red color represents flow above the retinal pigment epithelium (RPE) and the green color represents flow below the RPE. Segmentation boundaries are depicted by dotted yellow lines with the upper boundary following the outer plexiform layer (OPL) and the lower boundary following Bruch’s membrane (BM). (D) Horizontal B-scan without flow or segmentation lines showing the “kissing sign” which corresponds to the loss of the outer nuclear layer and the juxtaposition of the outer plexiform layer to the RPE (yellow arrow).

 

Treatment

Anti-VEGF therapy is currently the standard-of-care for exudative AMD.4 It has been shown to improve visual acuity and cause regression of the neovascular lesions. There are several anti-VEGF agents available for the treatment of neovascular AMD, and the choice of which anti-VEGF agent to use often depends on the cost and perceived differences in efficacy for each patient. Newer anti-VEGF therapies that have longer duration of action and are potentially more efficacious are currently being introduced, and their place in the treatment of exudative AMD will be revealed over time.

 

References

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