Choroidal neovascularization (CNV) is an eye condition characterized by the abnormal growth of new blood vessels originating from the choroid, a vascular layer beneath the retina. These new vessels break through a membrane called Bruch’s membrane and can extend into the sub-retinal pigment epithelium or subretinal space. This abnormal growth can lead to leakage of fluid or blood, damaging the retina and potentially causing significant vision loss. Treatments aim to preserve eyesight by managing this vessel growth and leakage.
Understanding Choroidal Neovascularization
The retina is the light-sensitive tissue at the back of the eye responsible for converting light into signals sent to the brain. In CNV, fragile new blood vessels grow from the choroid, the eye’s middle vascular layer, into the subretinal space beneath the retina. These abnormal vessels are prone to leaking fluid and blood, disrupting the delicate structure of the retina and damaging photoreceptor cells. This damage can lead to symptoms such as blurry central vision, distorted images, or blind spots.
The most common cause of CNV is age-related macular degeneration (AMD), specifically its “wet” or exudative form. In wet AMD, an excess of Vascular Endothelial Growth Factor (VEGF), a protein that stimulates new blood vessel growth, is produced by the retinal pigmented epithelium (RPE), a cell layer in the outermost retina. Other less frequent causes of CNV include high myopia, which involves an elongated eyeball that stretches the retina, and inflammatory conditions like uveitis or ocular histoplasmosis. Trauma or certain genetic conditions can also disrupt the barrier between the choroid and retina, leading to CNV.
Anti-VEGF Therapy
Anti-VEGF therapy is the primary treatment for choroidal neovascularization, directly targeting the abnormal blood vessel growth. Vascular Endothelial Growth Factor (VEGF) is a protein that stimulates the formation of new, often leaky, blood vessels in the eye. In CNV, an overproduction of VEGF leads to these unwanted vessel formations that cause fluid and blood leakage. Common anti-VEGF drugs include bevacizumab, ranibizumab, and aflibercept. These medications work by binding to and blocking the activity of VEGF, thereby inhibiting the growth of these abnormal vessels and reducing leakage.
These medications are administered directly into the eye through intravitreal injections, a procedure performed in an outpatient setting. The typical treatment regimen often begins with an initial “loading dose” phase, which may involve monthly injections for the first three to five months. Following this, a maintenance phase is usually adopted, with common approaches being “treat-and-extend” or “pro re nata” (PRN).
In a “treat-and-extend” regimen, injections are given at regular intervals, which are gradually lengthened if the eye remains stable, typically extending from four to twelve weeks. If signs of disease activity return, the interval is shortened. The “PRN” approach involves injections only when there are signs of active disease, requiring frequent monitoring. Anti-VEGF therapy has a high success rate in stabilizing or improving vision by significantly reducing fluid and hemorrhage and preventing further damage to the retina.
Other Therapeutic Approaches
While anti-VEGF therapy is the current standard, other treatment options exist for specific cases or as supplementary approaches. One such method is Photodynamic Therapy (PDT), which involves a light-activated drug, verteporfin. Verteporfin is administered intravenously and preferentially accumulates in the abnormal choroidal neovascularization. After a brief waiting period, a non-thermal laser light is applied to the affected area, activating the drug. This activation generates reactive oxygen species that damage the endothelial cells lining the abnormal blood vessels, leading to their closure and regression.
PDT was historically significant for treating certain types of CNV, particularly classic subfoveal lesions, and those associated with pathologic myopia or ocular histoplasmosis. However, its use has become more limited since the advent of anti-VEGF therapies, as PDT often requires retreatment within one to four weeks due to vessel reperfusion and does not typically improve visual acuity as effectively as anti-VEGF injections.
Another older treatment is laser photocoagulation, which uses a high-energy thermal laser to directly destroy the abnormal blood vessels. While effective at obliterating the vessels, a major drawback of this treatment is that it also damages the surrounding healthy retinal tissue, including photoreceptor cells, leading to permanent blind spots in the treated area. For this reason, laser photocoagulation is rarely used for CNV that affects the macula, the central part of the retina responsible for sharp, detailed vision. It is generally reserved for CNV lesions located far from the fovea, where visual impact from collateral damage would be less severe.
Managing Treatment and Monitoring Progress
Managing choroidal neovascularization treatment involves ongoing care and close monitoring to assess effectiveness and detect any recurrence. Regular follow-up appointments are a cornerstone of this management, typically scheduled at intervals determined by the treatment regimen and the patient’s response. During these visits, ophthalmologists use various diagnostic tools to evaluate the eye’s condition.
Optical Coherence Tomography (OCT) scans are frequently performed, providing detailed cross-sectional images of the retina and choroid. These scans help visualize fluid accumulation within or under the retina, as well as the structure of the abnormal blood vessels, guiding decisions on further treatment. Vision charts are also used to track changes in visual acuity, and some clinics may employ optical coherence tomography angiography (OCT-A) to visualize the blood vessel network without dye.
Patients should anticipate the need for multiple injections over time, as CNV is often a chronic condition requiring long-term management. The goal of treatment is to stabilize vision and prevent further loss, although some patients may experience improvement. Potential side effects from injections are generally temporary and mild, including temporary discomfort, eye redness, or the appearance of small floaters in vision.
Adherence to the prescribed treatment plan and regular follow-up schedule is important for maintaining vision and managing the condition effectively. While medical treatments are the primary focus, maintaining overall eye health through lifestyle factors such as not smoking and a nutritious diet can also support long-term well-being.