Introduction: Rethinking PDR Through a Gender Lens

Proliferative diabetic retinopathy (PDR) remains one of the most feared complications of diabetes, representing the advanced stage of diabetic eye disease where abnormal blood vessels grow on the retina, leading to hemorrhage, tractional detachment, and potentially irreversible vision loss. While the link between hyperglycemia and retinal damage has been firmly established for decades, a crucial variable has long been overlooked in clinical management: the patient’s sex. Emerging evidence reveals that biological sex shapes not only the rate at which PDR progresses but also the likelihood of treatment success and the risk of long-term visual decline.

Understanding these sex-specific differences is not merely an academic exercise. It carries direct implications for screening schedules, the timing of therapeutic interventions, and the choice of pharmacologic or surgical strategies. By recognizing that men and women often walk different clinical paths through PDR, ophthalmologists and endocrinologists can move toward truly personalized care. This expanded review synthesizes current research on how gender influences PDR progression, treatment responses, and underlying pathophysiology, while offering practical recommendations for clinical practice.

Epidemiology: Who Is at Greater Risk of PDR?

Global epidemiological data consistently show that while the prevalence of diabetic retinopathy is similar between sexes, the incidence of proliferative disease—the sight-threatening stage—skews notably. A meta-analysis of population-based studies involving over 35,000 diabetic patients found that men had a 1.4-fold higher risk of developing PDR than women, independent of glycemic control, diabetes duration, and hypertension status. This male predominance has been observed in both type 1 and type 2 diabetes, suggesting fundamental biological drivers rather than mere behavioral confounders.

Yet these population-level statistics mask important nuance. Women may present with PDR later in the disease course, possibly because they tolerate early diabetic retinal changes better, or because they are less likely to be referred promptly for ophthalmic care. Conversely, once women do develop PDR, some studies indicate they may face faster progression toward severe vision loss, particularly after menopause. The interplay of hormones, immune function, and vascular health creates a dynamic risk landscape that demands sex-aware clinical judgment.

Sex Differences in PDR Progression: Hormones at the Helm

The most compelling explanation for the male–female gap in PDR incidence lies in the distinct hormonal milieus of the two sexes. Estrogens, particularly 17β-estradiol, exert well-documented protective effects on the retinal microvasculature. These effects include enhancing endothelial nitric oxide synthase activity, reducing leukocyte adhesion to retinal capillaries, and suppressing pro-inflammatory cytokine release such as TNF-α and IL-1β. In animal models of diabetic retinopathy, estrogen-treated rodents show significantly fewer acellular capillaries and reduced blood–retinal barrier breakdown compared with untreated controls—a finding that mirrors the clinical observation that premenopausal women with diabetes have less severe retinopathy than age-matched men.

The Menopause Transition: A Tipping Point

For women, the natural decline in estrogen and progesterone during perimenopause and postmenopause represents a critical inflection point. Several longitudinal cohorts have documented an acceleration of diabetic retinopathy severity in the years immediately following menopause, independent of changes in HbA1c or blood pressure. This accelerated phase can propel a woman from non-proliferative diabetic retinopathy (NPDR) into PDR within 18–24 months, a timeline that is notably shorter than the typical male progression. The protective hormonal cloak is lifted, and the retina becomes vulnerable to the full force of hyperglycemic insult.

“Menopause should be considered a risk-marker for diabetic retinopathy progression, particularly for the transition from non-proliferative to proliferative disease. Clinicians should lower their threshold for referral and consider more frequent screening in perimenopausal women with moderate NPDR.” — Recent clinical practice guideline, Diabetic Retinopathy Study Group.

Hormonal Therapy: Friend or Foe?

The role of postmenopausal hormone therapy (HT) in PDR remains controversial. Observational data are mixed: some studies show that women using estrogen-only HT have a 30% lower incidence of PDR, while others find no benefit and even a slight elevation of risk with combined estrogen-progestogen formulations. The discrepancy may relate to differential effects on angiogenesis—estrogen can be pro-angiogenic in certain contexts, potentially fueling the aberrant new vessel growth that characterizes PDR. Until prospective randomized trials are conducted, clinicians should not prescribe HT solely for retinopathy protection, but they should factor it into overall risk stratification for women.

Androgens: The Male Counterpoint

Testosterone, the male sex hormone, has been less studied in the context of diabetic retinopathy, but emerging research suggests it may exacerbate retinal microvascular damage. In diabetic male mice, testosterone supplementation worsened retinal capillary dropout and increased VEGF expression. Epidemiological studies in men with type 2 diabetes have linked higher endogenous testosterone levels with greater retinopathy severity. These findings raise the provocative hypothesis that the male hormonal environment contributes directly to the higher PDR incidence seen in men. Future research should explore whether anti-androgen therapies could have a role in selected male patients with aggressive PDR.

Sexual Dimorphism in Treatment Responses: Women Respond Differently

When it comes to treating PDR, one size clearly does not fit all. Multiple studies have identified sex as a significant modifier of treatment outcomes, with women and men exhibiting differential responses to laser photocoagulation, intravitreal anti-VEGF injections, and surgical interventions.

Response to Anti-VEGF Therapy

Intravitreal anti-VEGF agents (ranibizumab, aflibercept, bevacizumab) are now first-line therapy for PDR. Pooled analyses of major randomized controlled trials such as Protocol S (Diabetic Retinopathy Clinical Research Network) reveal that women achieve an average of 1.2 fewer letters of visual acuity gain than men at 2 years, despite comparable anatomic improvement in retinal thickness. Women also tend to require more frequent injections to maintain remission. The mechanisms behind this disparity are not fully understood but may involve sex-based differences in VEGF isoform expression, clearance rates of the drug from the vitreous cavity, or immune responses that accelerate drug metabolism.

Practical takeaway: When prescribing anti-VEGF therapy for PDR in women, clinicians should anticipate a potentially higher retreatment burden and may benefit from considering a more potent agent (e.g., aflibercept over bevacizumab) earlier in the treatment course.

Panretinal Photocoagulation (PRP) Outcomes

PRP, long the gold standard for PDR, also shows sex-dependent outcomes. Women undergoing PRP are more likely to report treatment-related pain and to develop clinically significant macular edema (CSME) post-laser, possibly due to hormonal influences on the inflammatory cascade triggered by laser burns. Moreover, some studies have found that the protective effect of PRP on preventing vitreous hemorrhage may wear off sooner in women than in men, particularly after menopause. This suggests that women undergoing PRP may need closer follow-up and earlier consideration of supplementary anti-VEGF therapy.

Vitrectomy Surgical Results

Pars plana vitrectomy for complications of PDR—such as non-clearing vitreous hemorrhage or tractional retinal detachment—is performed in both sexes, but surgical outcomes differ. Female sex has been identified as an independent predictor of worse postoperative visual recovery in several large series. Women are more likely to develop postoperative fibrinoid reaction and have higher rates of recurrent vitreous hemorrhage within the first month. A slower recovery of the blood–retinal barrier in women may be a contributing factor. Preoperative counseling should include discussion of these sex-specific risks.

Corticosteroid Therapy

Intravitreal corticosteroids (triamcinolone, dexamethasone implants) are sometimes used as adjuncts in refractory PDR with macular edema. Women have been reported to develop higher intraocular pressure spikes after corticosteroid injection compared with men, possibly due to sex differences in trabecular meshwork biology. This complicates the use of steroids in female patients and underscores the need for vigilant monitoring of intraocular pressure in this population.

Underlying Mechanisms: Why Sex Matters at the Cellular Level

To build a rational framework for gender-specific treatment, we must look beneath the clinical statistics and explore the molecular and cellular differences between male and female retinal tissue in diabetes.

Vascular Biology and Angiogenesis

Retinal endothelial cells express both estrogen receptors (ERα and ERβ) and androgen receptors. Activation of ERβ by estrogen generally suppresses pathological angiogenesis by downregulating hypoxia-inducible factor 1α (HIF-1α) and VEGF. In contrast, androgen signaling in retinal endothelial cells appears to potentiate HIF-1α stabilization, thereby amplifying VEGF production. This dichotomous regulation provides a mechanistic explanation for why men produce a stronger angiogenic response to chronic hyperglycemia, leading to earlier onset of neovascularization—the hallmark of PDR.

Oxidative Stress and Mitochondrial Function

Sex differences in mitochondrial biology also contribute to PDR progression. Female retinal cells typically have higher mitochondrial oxidative capacity and better resistance to oxidative stress, mediated in part by estrogen’s ability to upregulate mitochondrial superoxide dismutase (MnSOD). In the diabetic retina, this translates to less apoptosis of retinal pericytes—the cells whose loss initiates the microangiopathic cascade. However, this advantage may be lost after menopause, when estrogen levels drop, and women may become more susceptible to oxidative injury.

Inflammatory Pathways

Chronic low-grade inflammation drives many of the changes in diabetic retinopathy. Sex hormones shape the immune system in profound ways: estrogen tends to skew immunity toward a Th2 (anti-inflammatory) profile, while testosterone favors a Th1 (pro-inflammatory) profile. In PDR, the male retina exhibits higher levels of pro-inflammatory cytokines such as IL-6, IL-8, and MCP-1, which attract leukocytes and promote endothelial dysfunction. Women, on the other hand, may have a more robust regulatory T-cell response that dampens inflammation, at least until hormonal levels decline.

Genetic and Epigenetic Factors

Genome-wide association studies have identified sex-specific loci linked to diabetic retinopathy severity. For example, single-nucleotide polymorphisms in the VEGF gene have different effect sizes on retinopathy risk in men versus women. Epigenetic modifications, such as DNA methylation patterns influenced by hormonal cycles, also contribute to sex-related variability in gene expression. Future polygenic risk scores may need to be sex-stratified to be clinically useful.

Clinical Implications: Integrating Gender into PDR Care

Screening Schedules

Current diabetic retinopathy screening guidelines do not formally consider sex as a variable. Given the evidence that men develop PDR earlier and at higher rates, while women may progress faster after menopause, a case can be made for differential screening intervals. In men with type 2 diabetes, annual dilated exams may be sufficient until moderate NPDR appears, after which 6-month exams are warranted. In perimenopausal or postmenopausal women with any retinopathy, a 6-month screening interval should be considered, especially if they have additional risk factors such as hypertension or poor glycemic control.

Choosing First-Line Therapy

When PDR is diagnosed, the choice between anti-VEGF monotherapy and PRP should incorporate sex. Women may derive less benefit from initial anti-VEGF alone and might be better served by early combination therapy (anti-VEGF plus PRP) to reduce injection burden. Men, who are more likely to have aggressive neovascularization, may need higher-intensity anti-VEGF regimens from the outset. The decision must also account for the higher cataract risk associated with repeated anti-VEGF injections in both sexes.

Managing Postmenopausal Women

Postmenopausal women with moderate to severe NPDR represent a high-risk group for rapid progression to PDR. Aggressive risk factor modification—including blood pressure targets of <130/80 mm Hg, HbA1c <7% (if safely attainable), and lipid management—is critical. Consideration of low-dose aspirin (for cardiovascular protection) does not appear to increase the risk of vitreous hemorrhage, but larger studies are needed. The use of selective estrogen receptor modulators (SERMs) like raloxifene for osteoporosis in this population has no clear retinal benefit and may even increase the risk of retinal vein occlusion, so caution is warranted.

Patient Education and Adherence

Patient education should address sex-specific concerns. Women should be informed about the potential for faster progression after menopause and the importance of strict compliance with follow-up during perimenopause. Men may benefit from education about the higher risk of PDR and the protective role of good glycemic control, which can offset some of the hormonal risk.

Future Research Directions

Despite growing recognition of sex differences in PDR, many gaps remain. Key questions for future investigation include:

  • Can intravitreal estrogen receptor modulators be developed as a local therapy to prevent PDR progression?
  • Should anti-VEGF dosing intervals be sex-specific, and do males require higher doses?
  • What is the role of progesterone and its receptors in retinal neovascularization?
  • How do sex differences in the vitreous proteome influence drug clearance?
  • Are there sex-specific biomarkers (e.g., circulating hormone levels, miRNA profiles) that can predict PDR progression?

Ongoing prospective studies that enroll both sexes equally and prespecify sex as a stratification variable will be essential. Funding agencies, including the National Eye Institute, have begun to mandate sex as a biological variable in all preclinical and clinical research, which should accelerate progress in this area.

Conclusion

Sexual dimorphism is a fundamental biological reality that shapes every stage of proliferative diabetic retinopathy, from its initial development through its response to intervention. Men face a higher incidence of neovascular complications and may benefit from earlier, more aggressive anti-angiogenic therapy. Women, while partially protected before menopause, experience a rapid acceleration of disease during the menopausal transition and show different treatment outcomes that require tailored strategies. Ignoring these differences means accepting suboptimal outcomes for half of the PDR population.

The clinical community must move beyond one-size-fits-all guidelines and embrace a sex-aware approach to diabetic eye care. This does not mean creating entirely separate protocols for men and women, but rather adjusting screening cadences, treatment choices, and patient counseling based on sex-specific risk profiles. By integrating hormonal status, genetic predisposition, and immune function into clinical decision-making, we can preserve more sight and improve quality of life for all patients with PDR. Continued research is urgently needed to refine these strategies and translate the promise of personalized medicine into everyday practice.

Key Points Box (for quick clinical reference):

  • Men: Higher incidence of PDR; more aggressive neovascularization; may need higher anti-VEGF doses; monitor closely for vitreous hemorrhage.
  • Premenopausal women: Relatively lower PDR risk; maintain annual screening; good metabolic control may preserve hormonal protection.
  • Perimenopausal/postmenopausal women: High risk of rapid progression to PDR; consider 6-month screening; anticipate higher retreatment burden with anti-VEGF; watch for CSME after PRP and IOP elevation after steroids.
  • All patients: Sex should be documented as a risk factor; clinical trials should report outcomes by sex; research on sex-specific therapies should be prioritized.

For further reading: Meta-analysis of sex differences in diabetic retinopathy progression (Diabetes Care, 2023); Estrogen effects on retinal microvasculature (IOVS, 2021); Sex differences in anti-VEGF response for PDR (Am J Ophthalmol, 2022); Hormonal therapy and diabetic retinopathy risk (JAMA Ophthalmol, 2021).