Retinal neovascularisation is a serious eye condition where abnormal, fragile blood vessels grow on the surface of the retina, the light-sensitive layer at the back of your eye. These new vessels can leak fluid and blood, threatening your vision and potentially leading to blindness if not caught and treated early.

What Is Retinal Neovascularisation?

Retinal neovascularisation refers to the growth of new blood vessels on the retina where they should not normally exist. The retina is the part of your eye that captures light and converts it into electrical signals that travel to your brain, allowing you to see. These new blood vessels develop in response to injury or disease affecting the eye, particularly when parts of the retina are starved of oxygen and nutrients.^[1]

Unlike the normal blood vessels in your eye, these newly formed vessels are abnormal in structure and function. They lack the proper tight connections between cells that healthy vessels possess, making them extremely fragile and prone to breaking easily. When these weak vessels rupture, they allow blood and fluid to leak into the retina and the surrounding areas of the eye. This leakage can cause immediate visual disturbances and, over time, lead to permanent damage to the delicate cells responsible for your sight.^[2]

The body creates these new vessels as a protective response, attempting to supply blood to areas that aren’t getting enough oxygen. However, rather than solving the problem, these abnormal vessels make things worse. They can cause the gel-like substance inside your eye, called the vitreous, to degenerate and contract, eventually leading to serious complications such as bleeding inside the eye and detachment of the retina from its normal position.^[3]

How Common Is This Condition?

Retinal neovascularisation is not among the most common eye conditions, but it represents a significant cause of vision loss worldwide. It typically occurs as a complication of other underlying diseases rather than appearing on its own. The condition most commonly affects people who have diabetes, particularly those with poorly controlled blood sugar levels, and individuals over the age of fifty who develop age-related eye diseases.^[2]

While exact global statistics specifically for retinal neovascularisation are not widely documented, the underlying conditions that cause it affect millions of people. For instance, age-related macular degeneration, one of the diseases that can involve neovascularisation, is the leading cause of vision loss in people over fifty in developed countries. Diabetic retinopathy, another major cause, affects a substantial portion of people living with diabetes, particularly those who have had the disease for many years.^[4]

What Causes Retinal Neovascularisation?

The root cause of retinal neovascularisation is typically a lack of oxygen reaching parts of the retina, a condition called retinal ischemia. When the retina’s normal blood supply becomes blocked, damaged, or insufficient, the affected tissue becomes starved of oxygen. This oxygen deprivation triggers a biological response where the retina releases chemical signals, particularly a protein called vascular endothelial growth factor (VEGF).^[4]

VEGF is a powerful substance that stimulates the growth of new blood vessels. In a healthy situation, this process is tightly controlled and helps with normal healing. However, in retinal ischemia, too much VEGF is produced, leading to the uncontrolled growth of abnormal blood vessels. These vessels sprout from existing retinal blood vessels and grow across the surface of the retina in tangled, disorganised patterns, completely unlike the orderly structure of normal blood vessels.^[7]

Several specific diseases and conditions can cause the retinal ischemia that leads to neovascularisation. Diabetes is one of the most common culprits, as chronically high blood sugar levels gradually damage the tiny blood vessels in the retina. Over time, these damaged vessels can become blocked or leaky, depriving areas of the retina of adequate blood flow. Other causes include blockages in the retinal veins or arteries, which can suddenly cut off blood supply to large sections of the retina.^[2]

Less commonly, retinal neovascularisation can result from eye trauma, chronic inflammation inside the eye, certain blood disorders like sickle cell disease, or even tumours within the eye. In rare cases involving premature infants, abnormal blood vessel growth can occur as part of a condition called retinopathy of prematurity, which happens when the retina’s normal blood vessel development is disrupted.^[7]

Who Is at Risk?

Certain groups of people face a higher risk of developing retinal neovascularisation due to underlying health conditions or lifestyle factors. Understanding these risk factors is important because early detection and management of the underlying causes can help prevent this serious complication.

People with diabetes, especially those whose blood sugar levels are not well controlled, are at significant risk. Diabetic retinopathy develops in many individuals who have had diabetes for a long time, and the advanced form of this condition, called proliferative diabetic retinopathy, is characterised primarily by retinal neovascularisation. The longer someone has diabetes and the poorer their blood sugar control, the higher their risk becomes.^[2]

Older adults, particularly those over fifty, face increased risk because age-related macular degeneration becomes more common with advancing years. When this condition progresses to its “wet” form, abnormal blood vessels grow from a layer beneath the retina called the choroid, which can extend into the retina itself. Although this is technically classified as choroidal neovascularisation, it involves similar processes and causes similar vision problems.^[3]

People with high blood pressure or cardiovascular disease have an elevated risk because these conditions can lead to blockages in the retinal blood vessels. A blocked vein or artery in the retina suddenly cuts off blood supply, creating ischemia that triggers new vessel growth. Those who have had a retinal vein or artery occlusion are particularly vulnerable and need careful monitoring.^[2]

Other risk factors include extreme nearsightedness, a history of eye injuries, chronic eye inflammation, blood clotting disorders, and smoking. Smoking in particular damages blood vessels throughout the body, including those in the eye, and significantly increases the risk of various retinal diseases. People with certain blood disorders, such as sickle cell disease, also face increased risk due to abnormal blood flow patterns in the tiny retinal vessels.^[1]

Recognising the Symptoms

One of the most challenging aspects of retinal neovascularisation is that it often develops silently in its early stages. Many people experience no symptoms whatsoever when the abnormal blood vessels first begin to grow. This is why the condition can progress significantly before being detected, making regular eye examinations crucial for at-risk individuals.^[3]

As the condition advances and the abnormal vessels begin to leak or bleed, symptoms start to appear. People may notice their vision becoming blurry or distorted, particularly in the central part of their visual field. Straight lines may appear wavy or bent, a symptom called metamorphopsia. This happens because fluid or blood accumulating under or within the retina causes it to lift and buckle, changing how light is processed.^[6]

Some individuals see dark spots, shadows, or areas of missing vision in their central sight. These can appear as grey or black patches that block part of what they’re trying to see. If bleeding occurs inside the eye, people might suddenly see numerous floating spots or cobweb-like strands drifting across their vision. In severe cases, vision can become significantly reduced or even lost entirely, particularly if a large bleed occurs or if the retina detaches.^[1]

Importantly, retinal neovascularisation typically does not cause pain. The lack of pain can be misleading, causing people to delay seeking medical attention even when they notice vision changes. However, any sudden change in vision, appearance of new floaters, flashes of light, or distortion in how straight lines appear should prompt immediate contact with an eye care professional. When it comes to retinal neovascularisation, time truly matters—the sooner treatment begins, the better the chances of preserving vision.^[6]

Can Retinal Neovascularisation Be Prevented?

While it may not be possible to prevent retinal neovascularisation entirely, particularly in people with certain underlying diseases, there are important steps that can significantly reduce the risk or catch the condition early when it’s most treatable.

For people with diabetes, maintaining good control of blood sugar levels is perhaps the most important preventive measure. Studies have consistently shown that keeping blood glucose within target ranges substantially reduces the risk of developing diabetic retinopathy and its complications, including neovascularisation. This means following prescribed diabetes treatments, monitoring blood sugar regularly, and working closely with healthcare providers to adjust medications as needed.^[7]

Managing other health conditions that affect blood vessels is equally important. Keeping blood pressure under control helps protect the delicate blood vessels in the retina from damage. Maintaining healthy cholesterol levels and treating cardiovascular disease reduces the risk of blockages in retinal arteries and veins. For people who smoke, quitting is one of the most beneficial things they can do for their eye health, as smoking damages blood vessels and increases the risk of numerous eye diseases.^[15]

Regular comprehensive eye examinations are essential, especially for people at higher risk. These exams allow eye care professionals to detect early signs of retinal problems before symptoms develop. For people with diabetes, annual dilated eye exams are recommended, and more frequent visits may be necessary if any retinal changes are detected. During these exams, the eye doctor can see the retina directly and identify early abnormal blood vessel growth or other warning signs.^[2]

If early signs of retinal disease are detected before neovascularisation develops, preventive treatments may be recommended. For example, people with diabetic retinopathy may receive laser treatment to prevent progression to the proliferative stage where new vessels grow. Similarly, those with blocked retinal veins may receive early intervention to reduce the risk of complications. Following through with recommended treatments and monitoring is crucial for preventing vision loss.^[7]

How the Disease Changes the Eye

Understanding what happens inside the eye during retinal neovascularisation helps explain why the condition is so serious and why treatment must begin quickly. The process involves a cascade of changes that progressively damage the delicate structures needed for vision.

The process typically begins with ischemia—insufficient oxygen reaching parts of the retina. This might happen because diabetes has damaged the small blood vessels, or because a clot has blocked a major vein or artery. When retinal cells don’t receive adequate oxygen, they release chemical distress signals, particularly VEGF. This protein normally helps regulate blood vessel growth, but in ischemic conditions, it’s produced in excessive amounts.^[4]

The elevated VEGF levels trigger a complex biological response. Blood vessel cells begin to multiply rapidly and migrate toward areas of ischemia. New vessel buds sprout from existing blood vessels and begin growing across the retina’s surface, often appearing as tangled networks. These vessels may also grow into the vitreous gel that fills the eye. Unlike normal retinal blood vessels, which develop in an organised pattern and have strong walls with tight junctions between cells, these new vessels are poorly formed and structurally weak.^[12]

Because the new vessels lack proper tight junctions, they are extremely leaky. Blood plasma seeps through their walls into the surrounding retinal tissue, causing swelling. Sometimes entire red blood cells escape, leading to bleeding within the retina or into the vitreous cavity. When blood fills the vitreous, it blocks light from reaching the retina, causing sudden vision loss. The leaked fluid can accumulate under the retina, lifting it away from its normal position and distorting vision.^[3]

As the condition progresses, fibrous scar tissue begins to form along with the new blood vessels. This creates fibrovascular membranes—combinations of abnormal blood vessels and scar tissue. These membranes can contract and shrink over time, tugging on the retina. This mechanical pulling can cause the retina to tear or detach completely from the back of the eye, a situation that requires emergency treatment to prevent permanent blindness.^[2]

The damage extends beyond just the physical disruption. The leaked blood and fluid contain substances that are toxic to the delicate photoreceptor cells—the rods and cones that actually capture light. Over time, these cells can die, leading to permanent vision loss even if the bleeding and leakage are eventually controlled. The macula, the central part of the retina responsible for detailed vision, is particularly vulnerable to damage from fluid accumulation and bleeding.^[6]