Choroidal neovascularization (CNV) is an eye condition characterized by the abnormal growth of new blood vessels. These vessels develop in a specific layer of the eye and can significantly affect vision. CNV can lead to serious vision impairment if not identified and managed.
Understanding Choroidal Neovascularization
The choroid is a network of blood vessels located beneath the retina, supplying oxygen and nutrients to the outer layers of the retina. In CNV, new, irregular blood vessels form within this choroid layer and grow through a thin barrier called Bruch’s membrane, extending towards or into the subretinal space or retinal pigment epithelium (RPE).
These newly formed vessels are often fragile. This fragility makes them prone to leaking fluid, blood, or lipids into the surrounding retinal tissue. The leakage can cause the retina to swell or form “blisters,” directly distorting vision. Over time, this fluid and blood accumulation can damage the light-sensing cells of the retina, known as photoreceptors, and lead to the formation of scar tissue, resulting in permanent vision loss.
Identifying Symptoms and Risk Factors
Individuals with choroidal neovascularization may notice vision changes. Common symptoms include distorted vision, where straight lines appear wavy or bent, known as metamorphopsia. Blurred central vision, the appearance of a blind spot or dark area in the center of vision (scotoma), and changes in color perception, where colors seem less vibrant, are also reported. These symptoms can develop suddenly or worsen rapidly, prompting an urgent visit to an eye care professional.
Several factors increase the likelihood of developing CNV. The most frequent cause is age-related macular degeneration (AMD), specifically its “wet” form, which is the most frequent cause. Other risk factors include high myopia (severe nearsightedness), ocular histoplasmosis syndrome, angioid streaks (small breaks in a retinal layer), and severe ocular inflammation (uveitis) can also lead to CNV.
Diagnosing Choroidal Neovascularization
Diagnosing choroidal neovascularization involves a series of tests to confirm abnormal blood vessels and assess their impact on the retina. A comprehensive dilated eye exam allows the ophthalmologist to inspect the retina for signs like fluid accumulation or bleeding. A visual acuity test measures the sharpness of vision, while an Amsler grid test can help detect distortions or blind spots in a patient’s central vision.
Advanced imaging techniques provide detailed views of the eye’s internal structures. Optical Coherence Tomography (OCT) is a non-invasive method that produces cross-sectional images of the retina and choroid, revealing fluid leakage and structural changes. Fluorescein Angiography (FA) involves injecting a fluorescent dye into a vein, allowing visualization of blood flow and leakage from abnormal vessels. Indocyanine Green Angiography (ICGA) is another dye-based imaging technique that provides clearer images of the choroidal circulation, helping identify CNV networks not easily seen with FA.
Treatment Options
The primary approach to treating choroidal neovascularization involves medications that inhibit the growth and leakage of abnormal blood vessels. Anti-VEGF (anti-Vascular Endothelial Growth Factor) injections are the common and effective treatment. These medications, such as ranibizumab, aflibercept, and brolucizumab, are administered directly into the vitreous cavity of the eye. They work by blocking VEGF, a protein that promotes the formation of new, leaky blood vessels, slowing or stopping their growth and reducing fluid leakage. Patients often require multiple injections over several months, with ongoing monitoring for repeat treatments.
Other treatments, while less common today, have been used for CNV. Photodynamic therapy (PDT) involves injecting a light-sensitive drug into the bloodstream, activated by a low-power laser directed at the abnormal vessels. This damages the unwanted blood vessels. Thermal laser photocoagulation, an older method, uses a high-energy laser to directly destroy the abnormal blood vessels. While effective, it can cause damage to surrounding healthy tissue and is rarely used now. The main objective of these treatments is to halt disease progression, minimize leakage, and preserve or improve vision.