Proliferative Diabetic Retinopathy: Causes, Symptoms & Treatment

Proliferative diabetic retinopathy (PDR) is the most advanced and sight-threatening stage of diabetic eye disease, defined by the growth of fragile new blood vessels on the retina or the optic disc. These vessels form in response to oxygen starvation in the retinal tissue, and because they are structurally weak, they bleed easily, pull on the retina, and can lead to rapid, severe vision loss. The condition develops after years of poorly controlled diabetes, though it can progress silently before a person notices any change in their sight.

How High Blood Sugar Leads to New Blood Vessel Growth

The chain of events that produces PDR starts with chronic high blood sugar damaging the tiny blood vessels that feed the retina. Over time, the walls of retinal capillaries weaken. Pericytes, the support cells wrapped around those capillaries, die off, and the capillaries themselves become blocked or empty. Research has shown that oxidative stress rises sharply in the diabetic retina: mitochondria become dysfunctional, pro-death proteins migrate within cells, and capillary cells undergo programmed death, forming what pathologists call “acellular capillaries” and “pericyte ghosts.”¹ These are among the earliest microscopic signs of retinopathy.

As more capillaries shut down, patches of retina lose their blood supply entirely. The oxygen-starved tissue responds by stabilizing a protein called HIF-1α, which in turn ramps up production of vascular endothelial growth factor (VEGF). VEGF is the body’s emergency signal to build new vessels, but in the context of the retina, those new vessels are a disaster. They grow in the wrong places, have leaky walls, and lack the structural support of normal vessels.² Once this abnormal vessel growth begins, the disease has crossed from nonproliferative to proliferative retinopathy.

Research tracking hypoxia markers in patients with worsening retinopathy has identified erythropoietin (EPO) as one measurable signal. When EPO levels exceeded about 27.5 mIU/mL, the risk of progressing from the nonproliferative stage to early PDR climbed substantially.³ The takeaway for patients is that PDR doesn’t appear overnight; it builds through a cascade of oxygen deprivation, inflammatory signaling, and vascular collapse that can be tracked and, in many cases, slowed before the proliferative stage arrives.

Where the New Vessels Grow and Why It Matters

Not all new vessel growth in PDR carries the same risk. Abnormal vessels can sprout on the optic disc (called NVD) or elsewhere on the retinal surface (called NVE). The distinction matters clinically because disc-based new vessels are more closely associated with serious vision loss.⁴ The factors driving NVD and NVE also appear to differ, which may explain why some patients develop one pattern and not the other. Imaging studies using ultra-widefield angiography have tried to quantify the threshold of retinal non-perfusion, the total area of dead capillary beds, that predicts progression to PDR. One study found that a threshold of roughly 118 disc areas of non-perfusion distinguished PDR eyes from severe nonproliferative eyes with about 85% specificity.⁵

Symptoms and What People Actually Notice

One of the most unsettling features of PDR is that it can be well established before you notice anything wrong. Early PDR may produce no symptoms at all. Vision stays clear as long as the new vessels haven’t bled and the macula remains unaffected. This is a major reason screening is so important: by the time symptoms appear, the disease is often advanced.

When symptoms do arrive, they tend to come suddenly. The most common presentation is a vitreous hemorrhage, where one of those fragile new vessels bleeds into the gel filling the eye. You might see a sudden shower of dark floaters, a red or brown tint to your vision, or, in a large bleed, near-total darkness in the affected eye.⁶ The bleed can sometimes clear on its own over weeks, but it often recurs.

Patients with PDR also report functional problems that go beyond what an eye chart captures. In interviews, people describe difficulty reading, trouble recognizing faces at a distance, red-tinted vision, and a persistent sense of visual unreliability that affects confidence and independence.⁷ The emotional toll, anxiety over unpredictable vision changes, fear of going blind, frustration with repeated treatments, is a consistent theme in quality-of-life research. Studies confirm that patients diagnosed with PDR score significantly lower on vision-related quality-of-life measures than patients at earlier stages of diabetic retinopathy.⁸

Complications Beyond Vision Loss

Left untreated, the abnormal vessels of PDR don’t just bleed. They can trigger a series of complications, each one harder to manage than the last.

Tractional retinal detachment: The new vessels grow along scaffolds of fibrous scar tissue. As that tissue contracts, it physically pulls the retina away from the back wall of the eye. If the detachment reaches the macula, central vision drops sharply and surgery becomes urgent.
Neovascular glaucoma: When VEGF and other inflammatory molecules spill forward into the front of the eye, abnormal vessels can grow across the iris and clog the eye’s drainage angle. Pressure inside the eye climbs, damaging the optic nerve. This form of glaucoma is particularly hard to treat because it involves both inflammation and structural blockage.²
Recurrent vitreous hemorrhage: Even after treatment, repeated bleeds can occur, each one clouding vision and sometimes requiring surgery to clear.

Neovascular glaucoma deserves special attention because it represents a point of no return for many patients. The pathway involves not just VEGF-driven vessel growth but also fibrosis driven by TGF-β that physically closes the drainage angle, making the elevated eye pressure resistant to conventional glaucoma drops.² Early treatment of PDR is the most effective way to prevent this outcome.

How PDR Is Diagnosed and Screened For

The gold standard for diagnosing PDR has long been a dilated eye exam combined with fluorescein angiography, where dye is injected into a vein and photographs reveal leaking or abnormal vessels. This technique is effective but requires a dye injection, takes time, and carries a small risk of allergic reaction.

Optical coherence tomography angiography (OCTA) has emerged as a powerful alternative. It maps retinal blood vessels without any dye, using the motion of red blood cells themselves as contrast. OCTA can visualize the fine capillary networks at different depths of the retina and pick up areas where blood flow has dropped out, which are the oxygen-starved zones that drive PDR.⁹ In head-to-head comparisons, ophthalmologists across training levels were able to identify new vessel growth on OCTA with accuracy equal to fluorescein angiography.¹⁰ A study of widefield OCTA for detecting retinal neovascularization found sensitivity and specificity ranging from 95% to 100% for both graders.¹¹

Artificial intelligence is also entering the screening picture. AI-assisted systems trained on retinal photographs have shown negative predictive values above 96% and positive predictive values above 90% in large screening populations, meaning they are very good at correctly ruling out disease and flagging those who need further evaluation.¹² One system, EyeArt, detected retinopathy requiring referral with about 96% sensitivity, compared with roughly 28% for dilated ophthalmoscopy alone.¹³ These AI tools are especially promising for expanding screening in primary care offices and underserved communities, where access to a retina specialist is limited.

Treatment With Laser Photocoagulation

Scatter laser photocoagulation, also called panretinal photocoagulation (PRP), was the first treatment proven to reduce the risk of severe vision loss from PDR, and it remains widely used. The procedure applies hundreds to thousands of tiny laser burns to the peripheral retina, deliberately destroying some of the oxygen-hungry tissue so that it stops sending VEGF signals. The effect is to starve the drive behind abnormal vessel growth.

PRP works, but it comes with trade-offs. It reduces the risk of severe vision loss, but the laser burns themselves cause some degree of visual field narrowing, reduced night vision, diminished color perception, and lower contrast sensitivity.¹⁴ For people who drive or work in dim environments, these side effects are not trivial. This is why the field has been moving toward treatments that preserve more peripheral vision while still controlling the disease.

Anti-VEGF Injections as an Alternative or Complement

Injecting drugs that block VEGF directly into the eye has transformed PDR management over the past decade. Several anti-VEGF agents are used: ranibizumab, aflibercept, and bevacizumab. Aflibercept binds VEGF with roughly 100-fold greater affinity than ranibizumab, which may allow longer intervals between injections in some patients.¹⁵

The landmark DRCR Protocol S trial compared ranibizumab injections head-to-head with PRP in nearly 400 treatment-naïve eyes with PDR. At two years, eyes treated with ranibizumab gained an average of about 3 letters of visual acuity, compared with essentially no change in the PRP group. The rates of quiescent PDR were similar in both groups, around 30 to 35%.¹⁶ Anti-VEGF injections also caused less visual field loss and fewer complications than laser.

A meta-analysis pulling together data across multiple trials confirmed that anti-VEGF reduced the rate of tractional retinal detachment compared with PRP (about 3% versus 12%), with high certainty of evidence. Short-term visual acuity outcomes and rates of diabetic macular edema also favored anti-VEGF. However, rates of vitreous hemorrhage and the need for vitrectomy surgery did not differ significantly between the two approaches over the long term.¹⁷ That last point is worth keeping in mind: anti-VEGF is not a cure, and if injections stop, the disease can rebound. In practice, many patients end up receiving both anti-VEGF injections and laser at different points, depending on how the disease responds.

When Surgery Becomes Necessary

Pars plana vitrectomy (PPV) is the surgical option reserved for complications that injections and laser cannot fix: vitreous hemorrhage that won’t clear on its own, tractional retinal detachment, or a combination of both. The procedure removes the vitreous gel (along with any blood and scar tissue), allowing the surgeon to lay the retina flat and apply laser directly.

Results depend heavily on why surgery was needed. One study found visual acuity improved from roughly 20/187 before surgery to about 20/69 after, with the most common postoperative issue being recurrent vitreous hemorrhage in about 39% of eyes, though only about 10% required a second surgery to clear it.¹⁸ A seven-year retrospective study reported even more dramatic improvement, from roughly 20/774 preoperatively to about 20/53 at last follow-up, in eyes that had PDR without retinal detachment.¹⁹ That same study found that eyes receiving PRP within six months before surgery and those given a pre-operative anti-VEGF injection had significantly lower rates of postoperative bleeding.

Eyes requiring reoperation for PDR complications tell a story about the value of early intervention. When the reason for the first surgery was a non-clearing vitreous hemorrhage, about 74% of eyes achieved 20/80 vision or better after reoperation. But when tractional retinal detachment was the reason, that number dropped to about 24%.²⁰ The message is clear: catching and treating PDR before it pulls the retina off gives a far better chance of preserving usable vision.

Blood Sugar and Blood Pressure Control

No eye treatment exists in isolation from what’s happening systemically. Intensive blood sugar control has consistently shown benefits for retinopathy progression. In the ACCORD follow-on study, retinopathy progressed in about 6% of patients who had been assigned to intensive glucose control, versus roughly 13% in the standard-control group.²¹

Blood pressure is a more complicated story. The UK Prospective Diabetes Study found that tighter blood pressure control reduced the formation of microaneurysms and slowed retinopathy progression over several years. But later trials, including the ACCORD blood pressure arm, found no significant effect of intensive blood pressure treatment on retinopathy progression.²² The current consensus is that blood pressure management helps overall cardiovascular health and probably helps the eyes, but blood sugar control is the stronger and more consistently supported lever for preventing PDR.

There’s a well-known paradox worth being aware of: rapidly improving blood sugar in someone with long-standing poor control can temporarily worsen retinopathy. This “early worsening” effect doesn’t mean tight control is bad; studies show the long-term benefits of good glucose control clearly outweigh the short-term risk. But it does mean your eye doctor should be monitoring you closely during any period of aggressive diabetes treatment adjustment.

Newer Therapies Targeting Multiple Pathways

Anti-VEGF injections were a leap forward, but they address only one piece of the biological puzzle. VEGF is the dominant driver of abnormal vessel growth, yet other molecular signals, especially angiopoietin-2 (Ang-2), also contribute to vascular instability, pericyte loss, inflammation, and fibrosis. Faricimab is a bispecific antibody designed to block both VEGF-A and Ang-2 simultaneously. Data pooled across six phase III trials suggest that this dual blockade has a greater effect on markers of vascular instability than aflibercept alone, including better control of neovascularization, leakage, and retinal inflammation.²³ One practical advantage is that the dual mechanism may allow longer intervals between injections, reducing the treatment burden that patients frequently cite as one of the hardest parts of living with PDR.

Disparities in Who Gets Screened and Treated

PDR does not affect everyone equally, and the reasons go beyond biology. In a nationwide U.S. cohort, Black patients with diabetic retinopathy were significantly more likely to report being treated with less respect and receiving poorer service at healthcare visits than White patients. Hispanic patients were more likely to report delaying care due to logistical barriers such as lack of childcare.²⁴ These barriers translate directly into later-stage disease at the time of treatment. A study of patients undergoing vitrectomy for PDR in an underserved population found that Black patients had significantly higher pre-operative HbA1c levels and were more likely to present with tractional retinal detachment, including detachments involving the macula, compared with Hispanic and White patients.²⁵ Macula-involving detachments carry a worse visual prognosis, so these disparities in access and timing translate directly into worse outcomes.

Expanding AI-based retinal screening to primary care clinics, pharmacies, and community health centers is one concrete strategy being pursued to close this gap. The technology already performs well enough to triage patients accurately, and it removes the bottleneck of needing a specialist to be physically present for every screening exam. Whether it actually reduces disparities will depend on whether the systems are deployed in the communities that need them most.