Understanding Proliferative Retinopathy

Proliferative retinopathy (PR) represents the most advanced stage of diabetic retinopathy (DR) and is a leading cause of preventable blindness among working-age adults worldwide. The condition is defined by the growth of new, abnormal blood vessels on the surface of the retina or the optic disc—a process known as retinal neovascularization. These new vessels are fragile, leaky, and prone to hemorrhage, leading to vitreous hemorrhage, tractional retinal detachment, and severe vision loss if left untreated.

Approximately 20–30% of patients with diabetes mellitus will develop some form of diabetic retinopathy, and among those, roughly 5–10% will progress to the proliferative stage within 10–15 years of diagnosis. Risk factors include poor glycemic control, hypertension, dyslipidemia, pregnancy, and longer duration of diabetes. Despite improvements in systemic management, the incidence of PR remains high, underscoring the urgent need for more effective and durable treatments.

The Pathophysiology of Abnormal Vessel Growth

Retinal neovascularization in PR is driven primarily by local hypoxia and upregulation of vascular endothelial growth factor (VEGF). Ischemic retina releases VEGF-A, which binds to receptors on endothelial cells, stimulating angiogenesis and increasing vascular permeability. Other growth factors, including placental growth factor (PlGF), fibroblast growth factor-2 (FGF-2), and angiopoietin-2 (Ang-2), also contribute to the complex angiogenic cascade. Chronic inflammation and pericyte loss further destabilize the new vessels, making them prone to leakage and rupture.

Understanding this molecular basis has led to the development of therapies targeting VEGF pathways, but the disease often progresses despite anti-VEGF treatment. This has motivated researchers to explore additional pathways and combination strategies, which are now being tested in a robust pipeline of clinical trials.

Current Standard of Care

For decades, panretinal photocoagulation (PRP) using laser was the gold standard for treating PR. PRP reduces the metabolic demand of ischemic retina and thereby suppresses VEGF production, but it can cause collateral damage, including peripheral visual field loss, night vision impairment, and exacerbation of macular edema. In recent years, intravitreal anti-VEGF injections—such as ranibizumab (Lucentis), aflibercept (Eylea), and off-label bevacizumab (Avastin)—have become first-line therapy for many patients because they directly neutralize VEGF and often produce rapid regression of neovascularization with less retinal destruction. However, anti-VEGF therapy requires frequent injections (monthly or bimonthly), poses a burden on patients and healthcare systems, and may lose efficacy over time due to tachyphylaxis or compensatory upregulation of other angiogenic factors. These limitations have sparked intense research into more durable and alternative approaches.

Recent Clinical Trials and Emerging Therapies

A wave of late-stage clinical trials is currently reshaping the therapeutic landscape for proliferative retinopathy. These studies address key unmet needs: longer dosing intervals, improved safety profiles, and treatments that target alternative mechanisms beyond VEGF.

Anti-VEGF Therapy Trials

Next-generation anti-VEGF agents are being evaluated for their ability to extend injection intervals and provide superior anatomic outcomes. Faricimab (Vabysmo), a bispecific antibody that binds both VEGF-A and Ang-2, has already demonstrated in the phase 3 TENAYA and LUCERNE trials that it can maintain vision gains with dosing every 16 weeks in neovascular age-related macular degeneration. Its application in PR is being investigated in the ongoing YOSEMITE and RHINE trials (diabetic macular edema) and the RHONE trial (proliferative diabetic retinopathy). Early data suggest faricimab may reduce the need for rescue laser and achieve rapid neovascular regression.

Similarly, brolucizumab (Beovu), a single-chain antibody fragment with high molar dose, showed in the KESTREL and KITE trials that it can maintain efficacy with twice-yearly injections for diabetic macular edema. Its role in PR is being explored in the CONDOR trial (phase 3, active-controlled). A high-dose formulation of aflibercept (8 mg, versus the standard 2 mg) is being tested in the PULSAR trial for neovascular AMD and the PHOTON trial for diabetic retinopathy, with results showing non-inferiority with dosing every 12–16 weeks. The PORT delivery system, a refillable implant for ranibizumab, is also under investigation to reduce injection burden.

These trials are registered on ClinicalTrials.gov (identifiers: NCT03622593 for faricimab in DME, NCT03946579 for brolucizumab in PR, NCT04423718 for high-dose aflibercept). Preliminary reports indicate that these newer agents can achieve comparable or greater anti-VEGF suppression while dramatically reducing visit frequency.

Gene Therapy Approaches

Gene therapy aims to provide a one-time, sustained expression of anti-angiogenic proteins, potentially eliminating the need for repeated injections. ADVM-022 (ixoberogene soroparvovec) is an adeno-associated virus (AAV) vector encoding aflibercept. In the phase 1 OPTIC study, a single intravitreal injection produced durable suppression of VEGF and reduction in retinal thickness for up to 3 years in patients with neovascular AMD. A phase 2/3 trial (INFINITY) is now enrolling patients with proliferative DR to evaluate safety and efficacy. Another candidate, RGX-314, uses AAV8 to deliver a ranibizumab-like antibody fragment and is being tested in the phase 2 ALTITUDE trial for DR (including PR).

Challenges include immune responses to the vector, variability of transgene expression, and potential long-term toxicity. Nonetheless, gene therapy represents a transformative paradigm. More information on these trials can be found in a recent review in Ophthalmology (2023).

Advances in Laser Treatment

Although anti-VEGF therapy has become dominant, laser remains an important tool, especially in resource-limited settings or when patients cannot adhere to injection schedules. Modern laser technologies aim to achieve the benefits of PRP while minimizing retinal damage. PASCAL (Pattern Scan Laser) delivers shorter, more uniform burns in a predefined array, reducing treatment time and pain. Navigated laser photocoagulation (Navilas) uses real-time eye-tracking and fundus imaging to deliver precise treatment to targeted areas, potentially sparing healthy retina. Micropulse laser uses subthreshold energy that selectively affects the retinal pigment epithelium without creating visible burns, thus reducing permanent scotomas. The CLARITY study (2017) showed that anti-VEGF monotherapy was non-inferior to PRP for PR, but many subsequent trials are evaluating combination approaches where navigated or micropulse laser is added to reduce injection frequency.

Ongoing trials such as NCT04160182 are comparing pattern scan laser (PASCAL) guided by ultra-widefield fluorescein angiography versus standard PRP. Early results suggest that targeted, less destructive laser may offer comparable regression of neovascularization with fewer side effects.

Combination Treatment Strategies

The rationale for combination therapy is that blocking multiple pathways simultaneously may produce synergistic effects and longer durability. The Protocol S study (DRCR.net) previously found that ranibizumab plus PRP was no better than ranibizumab alone for PR, but more recent trials are exploring novel combinations.

  • Anti-VEGF + laser: The RECOVERY trial (NCT03042117) evaluated ranibizumab with or without targeted laser photocoagulation of leaking microaneurysms in diabetic macular edema, but extrapolations to PR suggest that focal/directed laser may help reduce injection burden.
  • Anti-VEGF + steroids: Intravitreal dexamethasone implant (Ozurdex) combined with anti-VEGF is being tested for persistent diabetic macular edema and for neovascular regression in PR (trial NCT03385109). Early data show improved anatomic outcomes but increased risk of cataract and intraocular pressure elevation.
  • Anti-VEGF + anti-PDGF: Platelet-derived growth factor (PDGF) promotes pericyte survival and vessel maturation. A phase 2 trial combining ranibizumab with an anti-PDGF agent (E10030) failed to show significant benefit, but other preclinical models suggest that targeting PDGF may help normalize pathological vessels.

An important systematic review of combination approaches was published in Retina (2024), summarizing that while no single combination has yet proven superior to anti-VEGF monotherapy, ongoing trials continue to refine the optimal protocol.

Novel Targets and Investigational Drugs

Several novel molecules are entering the pipeline, targeting pathways beyond VEGF to address the complexity of PR.

  • Integrin inhibitors: Integrins αvβ3 and αvβ5 are expressed on activated endothelial cells and participate in angiogenesis. Risuteganib (Luminate), a small integrin inhibitor, is being studied in a phase 2 trial for diabetic retinopathy (NCT04522986). Early results indicate improved best corrected visual acuity in some patients.
  • Anti-Tie2 agonists: Faricimab targets Ang-2, which destabilizes vessels. Other agents, such as AKB-9778 (an Ang-1 mimetic), are designed to activate the Tie2 receptor, strengthening the blood-retinal barrier and reducing leakage. A phase 2 trial (NCT03198896) showed that AKB-9778 combined with ranibizumab improved diabetic macular edema compared to ranibizumab alone.
  • Complement inhibitors: The complement cascade is implicated in the inflammatory component of DR. Pegcetacoplan (Syfovre), a C3 inhibitor approved for geographic atrophy, is being explored for diabetic retinopathy in the phase 2 PIONEER trial (NCT04556596).
  • Small molecule kinase inhibitors: Oral inhibitors of VEGF receptors (e.g., pazopanib, sorafenib) have been tested in small pilot studies, but systemic side effects and poor ocular penetration have limited their development. New topical or intravitreal formulations may overcome these drawbacks.

These investigational agents represent the next frontier in PR management, aiming to provide non-invasive or longer-lasting options. Detailed summaries of these targets are available in recent reviews from Nature Reviews Disease Primers (2023) on diabetic retinopathy.

Implications for Patients and Clinicians

With over 200 active or recently completed clinical trials for proliferative retinopathy listed on ClinicalTrials.gov, the landscape is rapidly evolving. For clinicians, staying abreast of triple- or quadruple-blockade strategies and gene therapy results is essential for counseling patients and making evidence-based treatment choices. Patients should be informed that many of these promising therapies are not yet FDA-approved for PR; however, participation in clinical trials can provide early access and help advance care.

Key considerations for shared decision-making include the frequency of injections (from monthly to twice-yearly), the need for concomitant laser, the risk of endophthalmitis or retinal detachment with any intravitreal procedure, and the cost of newer agents. Telemedicine and AI-based screening tools are also being integrated into trial protocols to reduce visit burden and identify high-risk patients earlier.

Future Directions

The ultimate goal in proliferative retinopathy research is to achieve a durable, possibly permanent, regression of neovascularization with minimal treatment burden. Personalized medicine—guided by biomarkers such as aqueous VEGF levels, genetic polymorphisms, and advanced imaging—may help tailor therapy to individual patients. Artificial intelligence algorithms are being developed to predict progression from non-proliferative to proliferative stages, enabling earlier intervention. Regenerative medicine approaches, including stem cell-derived retinal pigment epithelium and endothelial cell replacement, are in preclinical stages.

As the global prevalence of diabetes continues to rise, the demand for effective, accessible treatments for PR will only grow. The clinical trials highlighted here represent a robust pipeline that promises to transform the care of this blinding disease within the next few years.