Article

CLINICAL: RETINA

USE OCTA TO VISUALIZE CNV

THIS DEVICE CAN HELP YOU PREVENT DEVASTATING VISION LOSS

CHOROIDAL NEOVASCULAR membranes (CNV) are pathologic blood vessels, typically thought to occur due to a defect in the retinal pigment epithelium (RPE)-Bruch’s membrane complex, causing release of angiogenic growth factor, such as VEGF, which signals a cascade of hypoxia, ischemia, inflammation and edema. If not detected early or untreated, CNV can result in devastating vision loss.

CNVs are commonly seen in AMD, pathologic myopia, central serous chorioretinopathy, angioid streaks, hereditary chorioretinal diseases, presumed ocular histoplasmosis syndrome and traumatic choroidal rupture. In some cases, no specific cause can be identified. These cases of CNV are known as idiopathic CNV.

To date, fluorescein angiography (FA) and indocyanine green angiography (ICG) remain the gold standard for aiding CNV diagnosis. However, drawbacks limit their widespread use, including invasiveness, inherent risks (discomfort, nausea and life-threatening anaphylaxis), contraindication in certain patient populations (children, pregnant patients and those with kidney disease), time (they take 10 to 30 minutes) and expense.

The good news: Optical coherence tomography angiography (OCTA), a rapid noninvasive technique, has emerged as a powerful tool in the detection of CNV.

Here, I provide an overview of CNV and how to use OCTA to identify the condition.

Learning Points

  • OCTA is a powerful tool in visualizing CNV and monitoring response to treatment.
  • OCTA is a safe, noninvasive and quick method as opposed to conventional angiography.
  • OCTA is patient friendly and convenient to use.
  • OCTA continues to revolutionize the way CNV and other retinovascular diseases are managed.

OVERVIEW

CNV is often the cause of severe, sudden and usually irreversible loss of vision due to exudation, subretinal hemorrhage and/or RPE detachment. Based on lesion type, size and characteristic feature, treatment — even anti-VEGF therapy — may differ significantly.

For example, patients with large CNV lesions had worse VA outcome in response to treatment with anti-VEGF, according to a 2012 American Journal of Ophthalmology study.

CNV falls under three types: type 1, limited to the sub-RPE space, commonly occurring in AMD patients; type 2 extending into the sub-retinal space, observed in angioid streak or pathologic myopia; and type 3, also called retinal angiomatous proliferation, corresponding to intraretinal CNV.

Based on FA patterns, CNV also are classified as: occult (type 1) poorly defined lesions, classic (type 2) well-defined lesions or a combination of both (mixed). CNV are further described based on their location, as subfoveal (underneath the fovea), juxtafoveal (1μm to 199μm from the fovea) and extrafoveal (200μm to 1500μm from the fovea).

Image A: A 69-year-old patient with exudative AMD CNV. Image B: OCTA of the vascularized CNV.
Courtesy of Mohammad Rafieetary, O.D., F.A.A.O.

A CNV vessel pattern has been described as having the following ICG features: The capillary-pattern CNVs are mainly composed of capillaries and minimal short, small-caliber feeder arterioles. The branching arteriolar pattern has long, large-caliber feeder arterioles with many branching arterioles. Mixed-pattern depicts features of both extremes. Presumably, all CNVs initially begin as capillary pattern, then progress and stabilize, or some new vessels become arteriolarized states, according to “Encyclopedia of the Eye.”

IDENTIFYING CNV VIA OCTA

OCTA, a noninvasive technology, has significantly improved the ability to detect CNV. It does not involve the risks of the aforementioned dye injections, and it captures high-resolution images of various layers of the retinal vasculature in approximately three to four seconds per eye.

In addition, the device allows for simultaneous visualization of retinal and choroidal structural features, as well as functional information (i.e. blood flow) using motion contrast to detect erythrocytes movement.

Also, the technology provides a segmented view of the different layers, allowing for views of both the inner and outer retinal vasculature and the choriocapillaris. Thus, OCTA is an excellent tool to determine the location and size of CNV pathologic vascularization and its response to anti-VEGF.

OCTA has provided new insight into the pathologic vessels of CNV. For example, an active capillary pattern is described as “lacy wheel” or “sea fan” lesions, according to 2015 studies in Retina. Also, a lesion with vessels associated with a central trunk has been described as a “medusa” or a glomerulus-shaped lesion. Inactive lesions with large mature vessels are described as “dead tree.” Another OCTA finding is a “perilesional halo,” or the presence of a dark ring surrounding the CNV.

These criteria provide a basis for analyzing and evaluating CNV activity, including degree of proliferation, persistence and/or recurrence. They also provide for stabilization and healing with vessels that become mature.

THE TAKEAWAY

Early diagnosis, precise structural and vascular assessment of CNV are crucial for initiating and guiding treatment to prevent progressive vision loss. The availability of OCTA has made the diagnosis of CNV patient-friendly and convenient for O.D.s. OM