Understanding Proliferative Diabetic Retinopathy in the Context of Comorbid Disease

Proliferative Diabetic Retinopathy (PDR) represents the advanced, vision-threatening stage of diabetic eye disease. It occurs when chronic hyperglycemia triggers retinal ischemia, leading to the release of vascular endothelial growth factor (VEGF) and the subsequent growth of abnormal, fragile new blood vessels on the retina and optic disc. These vessels are prone to hemorrhage, causing vitreous bleeding, fibrovascular proliferation, and tractional retinal detachment. The management becomes significantly more challenging when PDR coexists with other systemic conditions such as hypertension, cardiovascular disease (CVD), chronic kidney disease (CKD), dyslipidemia, and obesity. Each comorbidity can accelerate the progression of retinopathy, complicate treatment decisions, and increase the risk of adverse outcomes.

For clinicians, the key is to recognize that diabetic retinopathy is not an isolated ocular pathology but a manifestation of systemic microvascular and macrovascular damage. Therefore, a siloed approach—treating the eye without addressing the underlying systemic drivers—is insufficient. A comprehensive, multidisciplinary strategy is required to slow disease progression, preserve vision, and improve overall patient health.

The Impact of Comorbid Conditions on PDR Progression

Hypertension and Retinal Microvasculature

Hypertension is one of the most common comorbidities in patients with type 2 diabetes, affecting more than 70% of individuals. Elevated blood pressure increases hydrostatic pressure within the retinal capillaries, exacerbating endothelial dysfunction and promoting leakage. In the setting of PDR, uncontrolled hypertension can cause more frequent and severe vitreous hemorrhages, accelerate the formation of retinal neovascularization, and blunt the response to laser photocoagulation or anti-VEGF therapy. The landmark United Kingdom Prospective Diabetes Study (UKPDS) demonstrated that tight blood pressure control (less than 150/85 mm Hg) reduced the risk of diabetic retinopathy progression and vision loss by approximately 35%.

Treatment goals should align with guidelines from the American Diabetes Association (ADA), which recommend a target blood pressure of <130/80 mm Hg for most patients with diabetes. Many patients will require combination therapy, often including an ACE inhibitor or an angiotensin receptor blocker (ARB), which also provide renoprotective benefits.

Cardiovascular Disease and Treatment Considerations

Patients with PDR are at high risk for cardiovascular events, including myocardial infarction, stroke, and heart failure. Systemic inflammation and oxidative stress that drive atherosclerosis also promote retinal neovascularization. Furthermore, certain treatments for PDR can pose risks in patients with CVD. For example, intravitreal anti-VEGF agents (e.g., bevacizumab, ranibizumab, aflibercept) have been associated with a slight increase in systemic VEGF suppression, potentially raising the risk of arterial thromboembolic events, particularly in patients with a recent history of stroke or MI. However, the absolute risk is small, and for most patients, the ocular benefits far outweigh the systemic risks.

Cardiovascular disease also influences the choice of systemic medications. Thiazolidinediones (TZDs) have been linked to an increased risk of macular edema, though their effect on PDR is less clear. Sodium-glucose cotransporter-2 (SGLT2) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists have demonstrated cardiovascular and renal benefits, and emerging data suggest they may slow the progression of diabetic retinopathy in some patients. When managing PDR in a patient with pre-existing CVD, close collaboration with a cardiologist is essential to optimize both cardiac and ocular outcomes.

Chronic Kidney Disease and Its Unique Challenges

Chronic kidney disease (CKD), defined as an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m² or persistent albuminuria, is present in 20–40% of patients with diabetes. The microvascular damage underlying CKD is closely linked to retinal microangiopathy. In the Diabetic Retinopathy Clinical Research Network (DRCR.net) studies, patients with lower eGFR were more likely to have worse visual outcomes and required more intensive treatment for PDR.

Several practical issues arise when treating PDR in patients with CKD. First, the use of contrast agents for fluorescein angiography (FA) is relatively contraindicated in advanced CKD due to the risk of contrast-induced nephropathy. In such patients, optical coherence tomography angiography (OCTA) provides a noninvasive alternative for visualizing retinal vasculature. Second, the choice of anti-VEGF agent may be influenced by renal function. Aflibercept is cleared renally to some extent, though dose adjustments are rarely needed; nonetheless, ophthalmologists should be aware of the potential for prolonged systemic half-life in patients with severe renal impairment. Third, many patients with CKD have anemia, which can exacerbate retinal hypoxia and worsen PDR. Correction of anemia with erythropoiesis-stimulating agents may improve oxygen delivery to the retina, but these agents must be used cautiously because of potential cardiovascular risks.

Dyslipidemia and Lipid-Lowering Therapies

Lipid abnormalities, particularly elevated low-density lipoprotein (LDL) and triglycerides, are common in diabetes and contribute to the formation of hard exudates in the macula. While dyslipidemia is more closely associated with diabetic macular edema (DME) than PDR, there is evidence that fenofibrate—a peroxisome proliferator-activated receptor alpha (PPARα) agonist—reduces the need for laser treatment in patients with PDR. The FIELD and ACCORD Eye studies demonstrated that fenofibrate reduced the progression of retinopathy, possibly through anti-inflammatory and anti-angiogenic mechanisms independent of its lipid-lowering effects. Therefore, for patients with PDR and dyslipidemia, fenofibrate (in combination with a statin if indicated) may offer additional ocular benefits.

Comprehensive Management Strategies for PDR with Comorbidities

Coordinated, Multidisciplinary Care

The cornerstone of managing PDR in the presence of multiple comorbidities is a team-based approach. The ophthalmologist must communicate regularly with the patient’s primary care physician, endocrinologist, cardiologist, and nephrologist. Shared electronic health records and integrated care pathways can facilitate timely information exchange. At each visit, the ophthalmologist should review the patient’s blood pressure, HbA1c, eGFR, and lipid profile, and encourage optimal management of these parameters.

Optimizing Glycemic Control

Intensive glycemic control reduces the incidence and progression of PDR. The Diabetes Control and Complications Trial (DCCT) and its observational follow-up, the Epidemiology of Diabetes Interventions and Complications (EDIC) study, showed that early intensive control produced a long-lasting reduction in retinopathy progression—a phenomenon known as metabolic memory. However, caution is warranted in patients with long-standing diabetes, advanced PDR, or a history of cardiovascular disease, as rapid improvement in blood glucose can paradoxically worsen retinopathy in the short term (early worsening). This transient effect, though, is typically outweighed by the long-term benefits.

Tailoring Ocular Treatment to the Individual

Anti-VEGF Therapy

Intravitreal anti-VEGF injections are now first-line therapy for PDR, often replacing or delaying panretinal photocoagulation (PRP). In patients with comorbid hypertension or CKD, anti-VEGF agents are generally safe, but blood pressure should be monitored regularly. The Protocol S study from DRCR.net showed that ranibizumab was non‑inferior to PRP for treating PDR and had a lower incidence of peripheral visual field loss and fewer requirements for vitrectomy. For patients with renal compromise, the choice of agent may be driven by cost and availability; bevacizumab remains an effective and widely used off-label option.

Panretinal Photocoagulation (PRP)

Despite the shift toward anti-VEGF, PRP remains an important tool, particularly in resource-limited settings or for patients who cannot adhere to frequent injections. PRP reduces the risk of severe vision loss by ablating ischemic retinal tissue and decreasing VEGF production. However, in patients with chronic kidney disease who may have fragile retinal vessels due to hypertension or anemia, PRP must be delivered carefully to avoid exacerbating macular edema or causing hemorrhagic complications. PRP also has the disadvantage of causing visual field constriction and scotomata, which can be especially bothersome for patients with central vision loss from DME.

Vitrectomy

Pars plana vitrectomy is indicated for persistent vitreous hemorrhage after 3–6 months, tractional retinal detachment, or combined tractional-rhegmatogenous detachment. Patients with multiple comorbidities—especially those on anticoagulants or antiplatelet therapy—require careful perioperative planning. The presence of uncontrolled hypertension or severe CKD increases the risk of intraoperative bleeding and postoperative inflammation. A thorough preoperative assessment by the patient’s cardiologist or nephrologist is essential to minimize surgical risks.

Managing Systemic Medications and Drug Interactions

Polypharmacy is common in patients with diabetes and multiple comorbidities. The ophthalmologist should be aware of potential drug interactions that could affect the eye:

  • Anticoagulants and antiplatelet agents: Aspirin, clopidogrel, and warfarin do not appear to increase the risk of vitreous hemorrhage in PDR, but they can complicate surgical procedures. Bridging therapy may be needed for vitrectomy.
  • Thiazide diuretics: While generally safe, they can exacerbate hyponatremia, especially in elderly patients with CKD.
  • β-blockers: Nonselective β-blockers may mask hypoglycemic symptoms, but they are otherwise safe in PDR.
  • ACE inhibitors/ARBs: These are recommended for patients with hypertension and/or albuminuria. They have no adverse ocular effects and may offer retinal protection through anti‑inflammatory mechanisms.
  • SGLT2 inhibitors: As noted, these may reduce retinopathy progression but require monitoring for euglycemic diabetic ketoacidosis and genital infections.

Special Considerations for High-Risk Populations

The Elderly Patient with PDR

Age is an independent risk factor for both PDR progression and comorbidities such as CVD, CKD, and hypertension. Older patients often have slower clearance of anti-VEGF agents and may be more prone to systemic side effects. Falls from visual impairment are a major concern; preserving peripheral vision through judicious PRP is important. Comprehensive geriatric assessment should be considered.

Pregnancy and PDR

Pregnancy can accelerate the progression of PDR due to hormonal changes, increased blood volume, and potential worsening of hypertension or diabetes control. Strict glycemic control before and during pregnancy is essential. Anti-VEGF therapy is generally avoided in pregnancy due to theoretical risks to fetal angiogenesis; PRP remains the mainstay for treating PDR in pregnant women. Laser photocoagulation may be deferred until the second trimester if the retinopathy is not threatening central vision.

Lifestyle Modifications and Patient Education

Empowering patients to actively manage their health is critical. The ophthalmologist’s office should provide clear counseling on:

  • Blood glucose self-monitoring and dietary adjustments to achieve HbA1c targets.
  • Blood pressure monitoring at home and adherence to antihypertensive medications.
  • Smoking cessation: Smoking increases the risk of both PDR and cardiovascular events.
  • Dietary modifications such as reducing sodium and saturated fat intake.
  • Weight management through supervised physical activity, with appropriate modifications for those with CVD or advanced kidney disease.
  • Adherence to follow-up schedules for both eye and systemic health checks.

Patients should also be educated about the symptoms of vitreous hemorrhage (sudden floaters, flashes, or curtain-like vision loss) and instructed to seek immediate ophthalmologic attention if these occur.

Emerging Therapies and Future Directions

Several novel approaches are on the horizon for managing PDR in patients with comorbidities:

  • Implantable anti-VEGF devices: Devices such as the ranibizumab port delivery system can provide sustained drug release, reducing injection frequency—an advantage for patients with limited mobility or poor compliance.
  • Anti‑VEGF/Ang‑2 bispecific antibodies: Faricimab, which targets both VEGF-A and angiopoietin‑2, may offer improved durability and better control of retinal leakage in DME, and ongoing trials are exploring its role in PDR.
  • Topical therapy: Eye drops containing tyrosine kinase inhibitors or other agents are in development, aiming to reduce the need for invasive injections.
  • Systemic approaches: Fenofibrate, as mentioned, and newer agents such as the mineralocorticoid receptor antagonists (e.g., finerenone) may have retinoprotective effects by targeting inflammatory and fibrotic pathways.

Practical Recommendations for Healthcare Providers

  1. Screen early and often. Patients with diabetes and any comorbidity should have a dilated eye exam at diagnosis and at least annually. More frequent exams (every 3–6 months) are indicated for those with moderate or severe non‑proliferative diabetic retinopathy (NPDR) or PDR.
  2. Set clear treatment targets. HbA1c <7.0% (in most patients), blood pressure <130/80 mm Hg, LDL <100 mg/dL, and eGFR stabilization. Individualize targets based on patient age, life expectancy, and comorbidity severity.
  3. Choose ocular therapy based on patient profile. Anti-VEGF is first-line for most PDR. PRP is a reasonable alternative for patients who cannot follow up every 1–4 months for injections.
  4. Coordinate care proactively. Send summary notes to referring physicians, and request information about medication changes, recent lab results, and upcoming surgeries.
  5. Monitor for systemic side effects. After anti-VEGF injection, check blood pressure and ask about symptoms of cardiovascular events. Report any suspected systemic adverse events to the relevant specialist.
  6. Educate and empower. Provide written materials in the patient’s preferred language, and consider involving a diabetes educator or social worker for complex cases.

Conclusion

Managing proliferative diabetic retinopathy in patients with comorbid conditions is a demanding but essential aspect of comprehensive diabetes care. By integrating rigorous systemic control with appropriate ocular interventions, clinicians can reduce the risk of vision loss, improve quality of life, and address the broader vascular health of these high‑risk individuals. A collaborative, patient‑centered approach—grounded in current evidence and tailored to each patient’s unique combination of diseases—remains the foundation of effective management.

References and further reading:

  • American Diabetes Association. Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1). ADA Standards of Care
  • Gross JG, Glassman AR, Liu D, et al. Five‑Year Outcomes of Panretinal Photocoagulation vs Intravitreous Ranibizumab for Proliferative Diabetic Retinopathy: A Randomized Clinical Trial. JAMA Ophthalmol. 2018;136(10):1138‑1148. JAMA Ophthalmol
  • Chew EY, Davis MD, Danis RP, et al. The Effects of Medical Management on the Progression of Diabetic Retinopathy in Persons With Type 2 Diabetes: The ACCORD Eye Study. Ophthalmology. 2014;121(12):2443‑2451. Ophthalmology
  • National Eye Institute. Diabetic Retinopathy. NEI