Choroidal neovascular membrane (CNVM) is an eye condition involving the abnormal growth of new blood vessels. These vessels develop beneath the retina, within the choroid, potentially leading to significant vision impairment. Optical Coherence Tomography (OCT) is a non-invasive imaging technique used to diagnose and monitor this condition, guiding appropriate treatment strategies for patients.
Understanding Choroidal Neovascular Membrane
The term “choroidal neovascular membrane” describes the nature of this eye condition. “Choroidal” refers to the choroid, a network of blood vessels beneath the retina that supplies oxygen and nutrients. “Neovascular” indicates the formation of new, abnormal blood vessels, which are fragile and prone to leakage. “Membrane” describes the growth or sheet of these new vessels.
The retina, a light-sensitive tissue at the back of the eye, converts light into electrical signals. The macula, a small, central area of the retina, is responsible for sharp, detailed central vision needed for activities like reading. CNVM often develops in the macula, directly impacting this vision.
CNVM is most frequently associated with wet Age-related Macular Degeneration (AMD), a progressive eye disease. In wet AMD, abnormal blood vessels grow from the choroid into or under the retinal pigment epithelium (RPE), a layer of cells that supports the photoreceptors. This abnormal vessel growth is often triggered by changes in the RPE and Bruch’s membrane, a thin layer separating the RPE from the choroid, which can occur as part of the aging process.
Individuals with CNVM might notice symptoms affecting their central vision. These include blurred or distorted vision, where straight lines appear wavy or bent. They might also observe blind spots or a sudden decrease in central clarity.
The new blood vessels in CNVM are weak and prone to leaking fluid and blood. This leakage can accumulate under or within the macula, disrupting the delicate photoreceptor cells. Over time, this fluid and blood can form scar tissue, causing irreversible damage to the macula and leading to severe central vision loss if the condition is left untreated.
How OCT Imaging Reveals CNVM
Optical Coherence Tomography (OCT) is a non-invasive imaging test that provides detailed cross-sectional views of the retina and choroid. OCT uses light waves to create precise images of the eye’s internal structures. This technology allows ophthalmologists to visualize the distinct layers of the retina and choroid, revealing changes not visible during a standard eye exam.
OCT detects and characterizes CNVM by identifying specific pathological features. It shows fluid accumulation under or within the retina (subretinal or intraretinal fluid), which indicates leaky vessels. The imaging also reveals hemorrhage and the neovascular membrane itself.
OCT also identifies retinal pigment epithelial (RPE) detachment, where the RPE layer lifts from Bruch’s membrane. This detachment is caused by fluid or blood from the CNVM. The location and morphology of these features on OCT scans are important for classifying and guiding CNVM management.
Different types of CNVM exhibit distinct appearances on OCT, aiding in their classification and treatment planning. Type 1 CNVM grows beneath the retinal pigment epithelium (RPE). On OCT, it appears as a fibrovascular pigment epithelial detachment (PED) or a shallow, irregular RPE elevation.
Type 2 CNVM, also known as classic CNVM, grows into the subretinal space, above the RPE. OCT images show hyperreflective material beneath the neurosensory retina, often accompanied by subretinal or intraretinal fluid.
Type 3 CNVM, also called retinal angiomatous proliferation (RAP), originates from the retinal circulation and grows into the subretinal space and choroid. OCT scans show intraretinal hemorrhage, intraretinal edema, and deep intraretinal neovascularization connecting to the choroid.
Optical Coherence Tomography Angiography (OCTA) is an advanced, non-invasive extension of OCT that enhances CNVM detection. OCTA visualizes blood flow within retinal and choroidal vessels, allowing ophthalmologists to map the abnormal vascular network without intravenous dye injections. This provides a detailed, three-dimensional view of the neovascular complex, identifying its location, size, and activity for targeted treatment.
Treatment Approaches for CNVM
The primary treatment for CNVM involves anti-vascular endothelial growth factor (anti-VEGF) injections. VEGF is a protein that stimulates new blood vessel growth. In CNVM, excessive VEGF promotes the formation of leaky, abnormal vessels that damage vision.
Anti-VEGF medications block this protein’s activity, inhibiting new blood vessel growth and reducing leakage. This action helps stop CNVM progression, reduce fluid and blood accumulation, and can shrink the neovascular membrane. Common anti-VEGF drugs include ranibizumab (Lucentis), aflibercept (Eylea), bevacizumab (Avastin), and faricimab (Vabysmo).
Anti-VEGF medication is injected into the vitreous humor in the eye doctor’s office. Patients receive a topical anesthetic to numb the eye, making the procedure generally painless.
Multiple injections are usually required for effective CNVM management. The regimen involves an initial series of injections, often monthly, followed by ongoing injections as needed, based on the eye’s response and OCT findings. The goal of anti-VEGF therapy is to stabilize vision and prevent further loss, though many patients experience some vision improvement.
Other treatments, such as photodynamic therapy (PDT) or laser photocoagulation, are rarely used as primary CNVM therapies today. Anti-VEGF injections have largely superseded these older methods due to their superior efficacy and safety profile. They are now reserved for specific cases where anti-VEGF therapy is not suitable or effective.
Regular follow-up appointments and repeated OCT scans are important for managing CNVM. These evaluations allow the ophthalmologist to monitor the condition, assess treatment effectiveness, and determine if further injections are necessary. This monitoring helps ensure good long-term visual outcomes.