The Perfusion-Based Model of AMD: Moving Towards a Unifying Hypothesis

Area of Science:

• Ophthalmology
• Vascular Biology
• Genetics

Background:

• Age-related macular degeneration (AMD) is a complex condition influenced by age, genetics, and environment.
• The precise contribution of these factors to AMD initiation and progression is not fully understood.
• Existing research suggests a potential link between the blood supply to the outer retina and AMD pathogenesis.

Purpose of the Study:

• To re-examine existing literature on retinal blood supply for novel insights into AMD.
• To explore the role of hypoxia in the retinal pigment epithelium (RPE) and its connection to AMD features.
• To propose a perfusion-based model for AMD, integrating genetic and environmental risk factors.

Main Methods:

• Literature review focusing on the choriocapillaris and outer retinal vascularization in AMD.
• Analysis of genetic risk factors in relation to vascular pathophysiology.
• Examination of environmental factors like diet, smoking, and metabolic syndrome acceleration of AMD.

Main Results:

• Hypoxia in the RPE can induce AMD-like features, including photoreceptor degeneration.
• The macula's choriocapillaris is uniquely susceptible to hypoperfusion, leading to ischemia and hypoxia.
• Vascular loss and reduced blood flow in the choriocapillaris are early indicators of AMD.
• Complement-related genes are implicated in vascular insult, affecting vessels from large tributaries to the choriocapillaris.
• HTRA1, linked to small vessel disease, is found in the choriocapillaris of AMD patients.
• Ageing contributes to atherosclerosis, mirroring vascular changes in AMD.
• Lifestyle factors and metabolic syndrome accelerate both atherosclerosis and AMD.
• A perfusion model explains both soft drusen-associated and subretinal drusenoid deposit-associated AMD phenotypes.
• Chronic hypoperfusion is common to both AMD phenotypes, impairing the neurovascular unit.

Conclusions:

• AMD can be conceptualized as an end-organ vascular disease.
• Chronic hypoperfusion at the neurovascular unit is a common pathway in AMD pathogenesis.
• A unifying hypothesis for AMD may emerge from understanding its vascular underpinnings.