The Role of Anti-VEGF Therapies in Neovascular Age-Related Macular Degeneration (nAMD)

Introduction

Age-related macular degeneration (AMD) is the leading cause of vision impairment and irreversible blindness among individuals over the age of 55 in developed countries [1, 2, 3]. It is characterized by progressive damage to the macula, a key component of the eye’s retina. Since the retina is responsible for converting light into neural signals essential for vision, any damage can severely impair both central and peripheral vision, significantly impacting the quality of life for millions of people. AMD is categorized into two primary subtypes: the atrophic (dry) form (aAMD), which accounts for approximately 80-90% of cases, and the neovascular (wet) form (nAMD), responsible for the remaining 10-15% of cases [1, 2, 3]. While aAMD progresses slowly, primarily causing gradual retinal thinning and degeneration, nAMD progresses more rapidly and is characterized by choroidal neovascularization (CNV). CNV is the pathological formation of fragile blood vessels beneath the retina that leak fluid and blood, leading to swelling, retinal damage, and vision impairment that, when left untreated, can become permanent [1, 2, 4]. However, additional mechanisms beyond CNV, such as increased vascular permeability, referring to the heightened leakage of fluid and blood from retinal blood vessels, and inflammation, can also contribute to fluid accumulation in the retina, exacerbating disease progression [1, 4-6]. 

Central to these pathological processes is the overexpression of vascular endothelial growth factor (VEGF), a family of proteins and receptors that are the primary drivers of CNV by directly stimulating the growth of abnormal blood vessels in the retina, especially in nAMD. In response, anti-VEGF therapies—such as Aflibercept, Brolucizumab, and Ranibizumab—have emerged as the primary treatment strategy for nAMD. These agents differ in molecular structure, VEGF-binding mechanisms, tissue penetration, and durability, making comparative evaluation essential for tailoring treatments to patient needs [1, 4-6]. 

However, these treatments are not without drawbacks. They require frequent intravitreal injections—direct administrations of medication into the vitreous humor, the gel-like substance inside the eye—which can lead to side effects such as inflammation and drug resistance [2, 3, 6, 7]. Inflammation resulting from intravitreal injections may affect the retina or surrounding ocular tissues and, in some cases, contribute to further retinal damage [2, 3, 7]. If not promptly managed, this inflammation can potentially impair vision. As a result, many patients remain at risk of suboptimal treatment outcomes. While anti-VEGF therapies are the standard of care, their drawbacks highlight the need for further research into improving treatment effectiveness and accessibility. This review aims to compare the molecular mechanisms, therapeutic efficacy, and limitations of current anti-VEGF agents in treating nAMD. In doing so, it underscores the importance of personalized treatment decisions and ongoing innovation to enhance long-term outcomes for patients.

Mechanisms of VEGF and Anti-VEGF Therapy

Anti-VEGF agents block VEGF proteins by preventing them from selectively binding to the VEGFR-2 and VEGFR-3 receptors present on endothelial cells, which are the thin, specialized cells that form the inner lining of blood vessels under the retina [1, 2, 4-6]. VEGFR-2 plays a central role in mediating endothelial cell proliferation and increasing vascular permeability, leading to fluid and protein leakage into the retinal layers [6]. VEGFR-3 is activated by VEGF-C and VEGF-D, molecules that promote pathological angiogenesis (the formation of new blood vessels from pre-existing ones) and lymphangiogenesis (the formation of lymphatic vessels) [6]. VEGF-A is the primary VEGF protein involved in both normal and abnormal blood vessel formation, and it primarily signals through VEGFR-2. Under normal physiological conditions, VEGF-A regulates endothelial cell function to maintain proper blood vessel formation and homeostasis. However, in pathological conditions, such as in age-related macular degeneration (AMD), VEGF-A is overexpressed or dysregulated, leading to abnormal endothelial cell proliferation. This uncontrolled growth increases vascular permeability, promoting the development of choroidal neovascularization (CNV) and further contributing to fluid leakage into retinal tissues [2, 6]. Simultaneously, this process generates reactive oxygen species, exacerbating oxidative stress, inflammation, and abnormal vessel growth, particularly under hypoxic conditions, which occur when the flow of oxygenated blood to retinal tissues is compromised [1, 2, 6]. These interconnected mechanisms—ranging from VEGF-A binding and receptor activation to inflammatory and oxidative responses—highlight the multifactorial pathogenesis of nAMD. CNV progression occurs in stages that include endothelial cell activation, migration, and proliferation, followed by abnormal blood vessel development and leakage into retinal tissues. Therefore, anti-VEGF agents must interrupt VEGF-A signaling across these stages to effectively prevent disease progression and preserve vision [6].

There are two primary molecular mechanisms by which anti-VEGF agents inhibit VEGF activity. One involves decoy receptor binding: Aflibercept is a fusion protein that mimics natural VEGF receptors. It binds directly to VEGF-A with high affinity, sequestering it and preventing its interaction with VEGFR-2 and VEGFR-3 on endothelial cells [2, 5, 6, 9]. The second mechanism involves antibody-based neutralization: Brolucizumab, a humanized single-chain antibody fragment, binds directly to VEGF-A and blocks its ability to activate its receptors. Its small molecular size allows for deeper retinal penetration and longer intraocular durability [2, 5, 6]. Similarly, Ranibizumab, a monoclonal antibody fragment, also binds specifically to VEGF-A, but due to its larger size, it exhibits comparatively less tissue penetration [2, 5, 6, 9, 10].  By disrupting VEGF-A’s ability to activate its receptors and the downstream signaling pathways, these anti-VEGF agents suppress CNV, minimizing fluid leakage and reducing retinal swelling. [1, 2, 6].

Efficacies of Aflibercept, Brolucizumab, and Ranibizumab

When assessing the efficacy of anti-VEGF agents, such as Aflibercept, Brolucizumab, and Ranibizumab, researchers and clinicians consider several key factors: (1) improvement in Best Corrected Visual Acuity (BCVA); (2) anatomical changes in the retina, such as reduced retinal thickness and fluid accumulation; and (3) injection frequency and dosing schedules [1, 2]. Anti-VEGF therapies, including Aflibercept (Eylea), Brolucizumab (Beovu), and Ranibizumab (Lucentis), are administered via intravitreal injections, each differing in their mechanisms of action and dosing regimens. Aflibercept, a recombinant protein that acts as a decoy receptor, binds to various isoforms of VEGF-A, VEGF-B, and placental growth factor, with an initial dosing regimen of once every 4 weeks, transitioning to every 8 weeks after 3 months [5, 6, 9, 10]. Similarly, Brolucizumab, a humanized antibody fragment targeting all VEGF-A isoforms, follows a comparable schedule to Aflibercept, except that the only difference is that the transition is every 8 to 12 weeks [5, 6, 10]. Ranibizumab, another humanized antibody fragment targeting VEGF-A, typically starts with dosing every 4 weeks and can extend to every 12 weeks after 4 months [1, 2, 5, 6, 9, 10].

These efficacy outcomes include BCVA improvement, fluid reduction, and CNV suppression. Studies comparing these therapies highlight some distinct advantages of Brolucizumab and Aflibercept. Particularly, Brolucizumab has been noted to have an effective ability to bind, with high affinity, to VEGF-A isoforms [1]. For example, Kopiejka et al. (2022) found that Brolucizumab led to substantial reductions in both intraretinal and subretinal fluid, as well as a decrease in CNV membrane activity, outperforming Aflibercept in these anatomical measures [1]. This is significant because fluid accumulation and CNV are major contributors to vision loss in nAMD. Brolucizumab’s ability to effectively target these issues suggests it may be a more potent therapeutic option, especially in cases with significant fluid buildup. Similarly, Mishra et al. found that Brolucizumab is effective in reducing retinal fluid and macular thickness, alongside notable improvements in BCVA [8], supporting its potential advantages over other treatments. Dugel et al. noted that while Aflibercept and Brolucizumab produced similar improvements in BCVA, Brolucizumab required fewer injections to achieve comparable results [10]. This reduced injection burden could improve patient convenience and long-term adherence, making Brolucizumab a more efficient option for managing nAMD. 

Comparisons between Aflibercept and Ranibizumab, as highlighted by Gillies et al., demonstrated that Aflibercept provides a more substantial reduction in CNV size and slightly better stabilization of visual acuity over time [5]. These findings are significant because they underscore Aflibercept's effectiveness in controlling the progression of CNV, an important factor in preventing further visual deterioration. Supporting this, Almeida et al. found that both Aflibercept and Brolucizumab outperformed Ranibizumab in a vision recovery metric algorithm known as Advanced VitreoRetinal Analytics (AVRA), which tracks the rate of visual improvement in patients. AVRA uses three key metrics: Vision Recovery Velocity (VRV), which measures the speed of visual improvement or loss (letters per unit time); Injection Momentum (InjMom), which reflects the treatment burden by multiplying the number of injections by the VRV; and Vision Recovery Acceleration (VRA), which measures the change in VRV over time.  [11]. In this study, Aflibercept and Brolucizumab showed faster rates of visual improvement, with average gains of 0.44 and 0.56 letters per month, respectively, compared to 0.30 letters per month for Ranibizumab. This suggests that both Aflibercept and Brolucizumab result in more rapid improvements in visual acuity, which may be particularly beneficial for patients seeking to regain functional vision quickly [10]. These findings suggest that Aflibercept and Brolucizumab could provide a more proactive approach to treating nAMD, addressing both the structural changes and functional outcomes more efficiently. This faster rate of improvement could also contribute to a reduced burden of disease progression, allowing for a better long-term prognosis. AVRA stipulates that the ideal VEGF inhibitor would have a high positive VRV (more letters gained per unit time), low InjMom (requiring fewer injections), and a VRA close to zero (indicating stable vision over time) [11].

While all three anti-VEGF agents are effective in treating nAMD, Brolucizumab and Aflibercept show notable advantages in terms of fluid resolution, CNV reduction, and treatment efficiency, making them more favorable for long-term management. However, the choice of therapy should be individualized, taking into account patient-specific factors and potential adverse effects. 

Side Effects and Limitations 

Despite their demonstrated efficacy, Brolucizumab, Aflibercept, and Ranibizumab each have limitations that must be considered when selecting the most suitable treatment for patients. One major concern is the frequency of injections. As they occur in the eye, frequent injection carries a risk of complications such as infection or retinal damage, and it is in the best interest of patients to reduce the number of injections when possible. Gillies et al. conducted a study that aimed to reduce the number of clinical visits for nAMD patients by comparing the efficacy of Ranibizumab and Aflibercept in correlation to injection frequency over 12 months [5]. The study found that both treatments required a similar number of injections, with a mean of 9.7 injections in the first year [5]. Mishra et al. highlighted the higher incidence of adverse events, such as intraocular inflammation, associated with Brolucizumab, particularly with frequent injections in certain patient groups [8]. This study suggests that while Brolucizumab may reduce injection frequency for some patients, there is still a trade-off between fewer injections and the potential for more severe side effects, raising the question of whether reducing the number of injections is worth the risk for certain patient groups. Similarly, Ricci et al. noted that Brolucizumab, although it may require fewer injections, still carries risks such as intraocular inflammation and pressure change, which are known potential complications of intravitreal injections [2]. Each additional injection not only increases the patient’s burden but also spins another roulette for serious ocular complications. As a result, clinicians must strike a balance between minimizing the number of injections, thereby reducing patient burden and treatment fatigue, and ensuring sufficient treatment to prevent disease progression. It’s important to note that inadequate therapy can lead to worsening vision, in addition to the risks of excessive injection, which can heighten the risks of elevated intraocular pressure (IOP) and retinal vasculitis. Ricci et al., Ma et al., and Zhang et al. noted that Brolucizumab showed favorable anatomical outcomes, including reductions in central retinal thickness and the stabilization of abnormal blood vessels in the choroid. While it maintained an overall good safety profile, concerns were raised about intraocular inflammation and retinal vascular events, particularly with the 6 mg regimen administered every 12 weeks or adjusted to every 8 weeks depending on disease activity [2, 7, 11]. Additionally, Brolucizumab has been associated with retinal artery occlusion, a blockage of blood flow through the central or branch arteries of the retina, alongside retinal vasculitis, an inflammation of the retinal blood vessels. These adverse effects may result from a delayed hypersensitivity reaction [7]. Although anti-VEGF treatments effectively manage neovascular age-related macular degeneration, they carry risks such as elevated intraocular pressure (IOP) and retinal vasculitis, which are influenced by injection frequency. Continuous monitoring and individualized treatment strategies are essential to mitigate these risks. Therefore, optimizing treatment regimens requires balancing effective VEGF suppression with minimizing the frequency of injections, while further investigating the long-term implications of these side effects. 

Conclusion 

Anti-VEGF therapies have revolutionized the management of neovascular age-related macular degeneration (nAMD) by targeting the underlying pathology of choroidal neovascularization and vascular leakage. By inhibiting VEGF, these agents reduce abnormal vessel growth and stabilize the retina, leading to significant improvements in best-corrected visual acuity (BCVA) and retinal structure. Among the available therapies, Aflibercept, Brolucizumab, and Ranibizumab each offer distinct molecular advantages—such as binding affinity, tissue penetration, and injection frequency—that influence their clinical effectiveness. However, biological differences among patients and the burden of frequent injections necessitate a personalized approach to treatment selection. Ultimately, while all three agents are effective, evaluating their comparative strengths and limitations is essential for tailoring therapy to optimize outcomes in diverse patient populations. 

About the Author: Arsen Rostomyan

In my UWP 102B course, we were tasked with writing a scientific literature review on a topic with substantial recent research. Given my passion for pursuing a career in ophthalmology and my experience working with patients facing various vision-related diseases, I chose to focus on neovascular age-related macular degeneration (nAMD). This topic aligns with my academic interests and professional aspirations while allowing me to engage with ongoing research in a field that impacts millions worldwide. Through my literature review, I aim to provide a comprehensive overview of current treatments and emerging therapies for nAMD. My analysis underscores the importance of innovation in addressing unmet clinical needs, such as improving treatment efficacy, reducing invasiveness, and enhancing patient outcomes. Additionally, I highlight the value of personalized medicine and the role of continued research in advancing our understanding of this complex disease. Ultimately, my work bridges existing knowledge with future possibilities, offering insights for clinicians, researchers, and policymakers. I hope that this review fosters informed decision-making and cultivates a deeper appreciation for the challenges and opportunities in treating nAMD. 

Author’s Note

As a Biochemistry and Molecular Biology major, I’m trained to think critically about the molecular mechanisms behind biological processes. I chose to write this review because of my clinical experiences with patients affected by age-related macular degeneration (AMD), which inspired me to explore its underlying biology. My passion for ophthalmology and prior research on cone opsin water permeability and retinal signaling further deepened my interest in AMD. Working as a technician in an ophthalmology clinic and observing surgeries firsthand also strengthened my commitment to the field. This review reflects both my academic background and professional aspirations, and I hope it offers readers a clearer understanding of the science and treatment behind AMD.

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