Choroidal neovascularization is a condition where abnormal blood vessels grow beneath the retina, threatening central vision and the ability to perform everyday tasks. Understanding this condition and recognizing its warning signs can make the difference between preserving sight and facing permanent vision loss.
Understanding Choroidal Neovascularization
Choroidal neovascularization, commonly known as CNV, occurs when new, abnormal blood vessels begin to grow from the choroid, which is the layer of tissue between the retina and the white outer wall of the eye. The choroid is normally filled with blood vessels that supply oxygen and nutrients to the outer parts of the retina. When these new vessels form, they break through a thin membrane called Bruch’s membrane and grow into areas where they shouldn’t be, either beneath the retinal pigment epithelium (the outermost layer of the retina) or directly under the retina itself.[1][2]
The term “neovascularization” simply means “new blood vessels.” While the body sometimes creates new blood vessels as part of normal healing, the vessels that form in CNV are fundamentally different. These abnormal vessels are fragile and poorly constructed. Unlike healthy blood vessels that maintain tight barriers, these new vessels are leaky. They allow fluid from the blood, and sometimes even red blood cells, to seep into the surrounding retinal tissue. This leakage can immediately distort vision because it forms what doctors describe as a “blister” in the retina, which is normally flat and smooth.[1][3]
Over the course of days to months, this leaked fluid can cause serious damage to the retina. It particularly harms the photoreceptors, which are specialized light-sensing cells called rods and cones that capture images and send them to the brain. When photoreceptors are damaged or killed, vision loss becomes permanent. The fluid accumulation and subsequent bleeding can lead to scarring of the retina, which further compromises visual function and can create lasting blind spots in the central field of vision.[1][3]
How Common Is Choroidal Neovascularization?
Choroidal neovascularization is a major cause of vision loss worldwide, particularly among older adults. In the general population, myopic CNV (CNV related to extreme nearsightedness) affects approximately 0.017% of adults in the United States, which translates to roughly 41,000 individuals. The prevalence increases dramatically with age, especially when CNV develops as a complication of other eye diseases.[5]
The condition most commonly develops in people who have age-related macular degeneration, or AMD. When patients with dry AMD progress to the wet form of the disease, CNV is the hallmark feature. Among women over the age of 85, approximately 15% have AMD, and a significant portion of these individuals may develop CNV. The aging population means that the number of people affected by CNV is expected to increase substantially in coming years, with projections suggesting a 50% rise in AMD-related cases before 2020.[1][16]
CNV can affect individuals across different age groups depending on the underlying cause. While it primarily impacts older adults through AMD, younger patients can develop CNV when they have extreme nearsightedness (high myopia), certain inflammatory conditions, or eye injuries. CNV occurs in approximately 5% to 10% of patients with pathological myopia, making it a significant cause of vision loss in working-age adults who have very strong prescriptions for nearsightedness.[4][11]
What Causes Choroidal Neovascularization?
The exact mechanisms that trigger choroidal neovascularization are not fully understood, but researchers have identified several key factors. The most important appears to be a protein called vascular endothelial growth factor, or VEGF. When the retinas of people with certain eye conditions produce too much VEGF, it acts as a signal that tells blood vessels to grow. In response to these elevated VEGF levels, new blood vessels sprout from the choroid and push their way through Bruch’s membrane into the retina.[1][3]
Several processes in the eye can lead to excessive VEGF production. One theory suggests that the retinal pigment epithelium, a thin layer of cells that normally maintains the health of photoreceptors, releases abnormal amounts of VEGF when it becomes damaged or stressed. This damage can occur through aging, disease, or physical trauma to the eye. The body interprets these distress signals as a need for more blood supply and responds by growing new vessels, but these vessels end up causing more harm than good.[6][15]
In eyes with pathological myopia, the mechanism may be somewhat different. Extreme nearsightedness causes the eyeball to become elongated and stretched. This stretching can create mechanical stress on the eye’s layers, leading to breaks or cracks in Bruch’s membrane called lacquer cracks. These cracks provide pathways for abnormal blood vessels to grow through. The stretching also thins the choroid, which may disturb normal blood flow and trigger the formation of new vessels as the eye attempts to compensate for reduced circulation.[4][11]
Inflammation and infection can also contribute to CNV development. Conditions such as histoplasmosis (a fungal infection), sarcoidosis, and other inflammatory eye diseases can damage Bruch’s membrane and the surrounding tissues. This damage appears to create an environment that promotes abnormal blood vessel growth. The body’s healing response to inflammation may inadvertently trigger the very processes that lead to CNV formation.[3][7]
Risk Factors for Developing CNV
Age-related macular degeneration stands as the most significant risk factor for developing choroidal neovascularization. Patients who already have dry AMD face the possibility that their condition will progress to wet AMD, which is characterized by CNV. The presence of large drusen (yellow deposits under the retina) measuring more than 125 microns increases the risk substantially. Approximately 7 million Americans have these large drusen, placing them at considerable risk for vision loss if CNV develops.[16]
Extreme nearsightedness represents another major risk factor, particularly in younger individuals. People with high myopia have elongated eyeballs that place stress on the retina and choroid. This anatomical change makes them more susceptible to lacquer cracks and subsequent CNV formation. The condition can develop in highly myopic individuals even when they don’t show other typical myopic fundus changes, making regular eye examinations particularly important for this group.[3][4]
Several demographic and lifestyle factors increase the risk of CNV. Advanced age is perhaps the most universal risk factor, as the incidence rises sharply in people over 60. Smoking significantly increases risk, with studies showing that smokers have three times the risk of developing CNV compared to non-smokers when other risk factors are present. High blood pressure and cardiovascular disease have also been linked to increased CNV risk, possibly because they affect blood flow in the small vessels of the eye.[7][23]
Genetic factors play a role in determining who develops CNV. Having a family history of AMD or CNV increases individual risk, suggesting inherited components to the disease. Certain genetic variations affect how the immune system responds to stress in the retina, which may make some people more prone to developing abnormal blood vessel growth. Race and ethnicity also appear to matter, with Caucasian populations showing higher rates of AMD-related CNV than other ethnic groups.[16]
Previous eye trauma or surgery can create conditions favorable for CNV development. Choroidal rupture from blunt trauma or complications from laser photocoagulation may damage Bruch’s membrane and trigger abnormal vessel growth. Certain rare genetic conditions like pseudoxanthoma elasticum and the presence of angioid streaks (breaks in Bruch’s membrane) also substantially increase CNV risk. Even benign conditions like optic disc drusen have been rarely associated with CNV formation.[3][7]
Recognizing the Symptoms
The symptoms of choroidal neovascularization often appear suddenly and can be quite alarming. The most common symptom is distortion of central vision, where straight lines appear wavy, bent, or irregular. This distortion, called metamorphopsia, happens because the leaked fluid creates an uneven surface on the retina. People may notice that door frames look curved, text on a page appears wavy, or the lines on a checkerboard or grid seem to bend.[1][2]
Another hallmark symptom is the appearance of a dark, gray, or blank spot in the central vision. This is called a scotoma, and it can be either central (directly in the middle of what you’re looking at) or paracentral (just off to the side of center). The scotoma represents an area where the retina is no longer functioning properly due to fluid accumulation or damage to photoreceptors. Unlike the normal blind spot everyone has where the optic nerve enters the eye, these scotomas interfere with critical central vision needed for reading, recognizing faces, and other detailed tasks.[1][4]
Blurred or decreased central vision is another common complaint. Objects may appear out of focus, colors may lose their brightness or appear differently between the two eyes, and contrast sensitivity may decline. Some people report difficulty seeing in low light conditions or notice that objects appear to be different sizes when viewed with each eye separately. These symptoms reflect the physical changes occurring in the retina as fluid accumulates and disrupts the normal arrangement of light-sensing cells.[2][4]
An important characteristic of CNV symptoms is that they are painless. Vision changes occur without any eye pain, redness, or discomfort. This absence of pain sometimes leads people to delay seeking care, which can be a critical mistake. The painless nature of CNV does not reflect its seriousness. When hemorrhaging occurs from the abnormal blood vessels, symptoms may appear more suddenly or worsen rapidly, sometimes over the course of just a few days.[2][7]
Some individuals may experience what feels like pressure behind the eye, though this is less common. Modern imaging techniques can now detect certain forms of CNV before symptoms even appear. These non-exudative (non-leaking) neovascular membranes are typically asymptomatic but can be identified during routine eye examinations, highlighting the importance of regular check-ups, especially for people with known risk factors.[8]
Preventing Choroidal Neovascularization
While choroidal neovascularization cannot always be prevented, especially when it develops as part of age-related macular degeneration, several strategies may help reduce risk or slow progression. For individuals with dry AMD, careful monitoring and lifestyle modifications may delay or prevent conversion to the wet form with CNV. Regular comprehensive eye examinations allow doctors to detect early warning signs and intervene before significant vision loss occurs.[1]
Smoking cessation represents one of the most important preventive measures. Studies have consistently shown that smoking increases the risk of both AMD and CNV development. People who stop smoking can reduce their risk over time, and those who never smoke maintain lower risk throughout their lives. The harmful effects of smoking on blood vessels throughout the body appear to extend to the delicate vessels in the eye, making this a critical modifiable risk factor.[7]
Managing systemic health conditions like high blood pressure, diabetes, and cardiovascular disease may help protect eye health. These conditions affect blood flow and vessel integrity throughout the body, including in the eye. Regular medical care, appropriate medications, and lifestyle modifications to control these conditions may reduce stress on the blood vessels in the choroid and retina.[23]
For individuals with high myopia, regular eye examinations are essential because CNV can develop even in relatively young adults with extreme nearsightedness. While the myopia itself cannot be prevented in most cases, early detection of CNV allows for prompt treatment. People with high myopia should be particularly vigilant about any changes in their vision and report them immediately to their eye care provider.[4][11]
Nutrition may play a role in prevention, particularly for age-related forms of CNV. While diet alone cannot prevent CNV, certain vitamins and nutrients have been studied for their potential protective effects on the retina. However, specific recommendations should come from healthcare providers based on individual risk factors and overall health status. Protecting eyes from ultraviolet light exposure through appropriate sunglasses may also contribute to long-term eye health, though direct links to CNV prevention remain under investigation.[16]
How CNV Affects the Body
Choroidal neovascularization creates a cascade of physical and biochemical changes in the eye that progressively damage vision. The process begins when Bruch’s membrane, which normally acts as a barrier between the choroid and the retina, becomes compromised. This can happen through age-related changes, mechanical stress, inflammatory damage, or other insults. Once breached, the abnormal blood vessels use these defects as pathways to grow from the choroid into spaces where they don’t belong.[2][6]
The newly formed vessels are structurally defective compared to normal blood vessels. They lack the tight junctions and supporting cells that keep healthy vessels from leaking. As blood flows through these fragile vessels, fluid components of blood seep out into the surrounding tissue. This fluid contains proteins and other substances that accumulate between or under the retinal layers, creating swelling and elevation of the normally flat retinal surface.[1][3]
The accumulated fluid has immediate mechanical effects on vision. It physically displaces the photoreceptors from their optimal position, disrupting the precise alignment needed for clear vision. Light entering the eye no longer focuses correctly on the photoreceptor layer, causing the blurred and distorted vision that patients experience. The fluid also interferes with the normal biochemical processes that photoreceptors need to function, further compromising their ability to capture and process light.[1]
Over time, the chronic presence of fluid and leaked blood products becomes increasingly destructive. The photoreceptors, which are highly specialized cells with specific metabolic requirements, cannot survive prolonged exposure to this abnormal environment. They begin to die, a process that is largely irreversible. The retinal pigment epithelium, which normally supports and nourishes the photoreceptors, also becomes damaged. It may detach from underlying layers, further disrupting the delicate relationship between these structures.[1][3]
The body’s attempt to heal the damage often makes matters worse. Inflammatory cells migrate to the area, and while they attempt to clear debris and repair tissue, they also contribute to scarring. Fibrous tissue and scar formation gradually replace the functional retinal tissue. This process, which can take months to years, results in a disciform scar, a thick area of fibrous tissue that permanently replaces the damaged retina. Areas of retina lost to scarring cannot be recovered, making early treatment crucial to prevent this irreversible outcome.[2][7]
The biochemical environment in eyes with CNV shows elevated levels of various growth factors and inflammatory mediators. Beyond VEGF, which promotes blood vessel growth, other molecules like angiopoietin-2 and various cytokines create an environment that perpetuates the abnormal vessel formation and leakage. Recent research has also implicated cholesterol accumulation in certain immune cells called macrophages, suggesting that lipid metabolism may play a role in CNV pathophysiology. Understanding these complex mechanisms has opened new avenues for treatment development.[6][10][19]