AMD Epidemiology, Genetics & Risk Factors

Overview

Age-related macular degeneration (AMD) is a progressive disease of the macula: the RPE, Bruch's membrane, and the overlying photoreceptors. It is the single leading cause of irreversible central vision loss in people over 65. Its risk profile looks different from glaucoma or diabetic retinopathy in one key respect: no single systemic disease drives it. Instead, age, a strong genetic component, and a handful of modifiable exposures, chiefly smoking, combine to determine who progresses.

Knowing who is at risk, and why, matters clinically because AMD splits early into two very different disease courses: dry (atrophic) and wet (neovascular). Both draw from the same epidemiologic and genetic risk pool, yet they diverge sharply in presentation and management, the subject of the companion page on AMD clinical features and classification.

Epidemiology & Prevalence

The over-65 threshold is not incidental. Incidence climbs steeply with each advancing decade past it, and the disease rarely presents earlier. Among racial groups, elderly Caucasians carry the highest prevalence, a disparity thought to reflect both genetic background and differences in macular pigmentation.

Dry (atrophic) AMD accounts for roughly 80% of cases and wet (neovascular, exudative) AMD the remaining 20%. The minority form nonetheless causes a disproportionate share of severe, rapid vision loss, since active choroidal neovascularization can bleed and leak fluid within days; geographic atrophy from dry AMD progresses over years instead.

Risk Factors

Age is the dominant non-modifiable risk factor. Of the modifiable exposures, chronic cigarette smoking carries the strongest and most consistent association with AMD progression. It has the clearest evidence base of any lifestyle factor, and it's the one most worth raising directly at the time of diagnosis, since quitting is an intervention a patient can act on immediately.

Other proposed associations (dietary fat, UV exposure, cardiovascular disease) are weaker and less consistently reproduced across studies. Smoking remains the headline modifiable risk factor to raise in counseling.

Individual risk can be quantified with the AREDS Simplified Severity Scale, which assigns each eye one point for large drusen (125 micrometers or larger) and one point for retinal pigment abnormality, for a combined score of 0 to 4. A score of 0 carries roughly a 0.5% five-year risk of progression to advanced AMD in at least one eye; a score of 4, with large drusen and pigment change in both eyes, raises that risk to roughly 50%. The scale turns a vague sense of elevated risk into a concrete number for the counseling conversation.

The AREDS2 trial tested whether adding ingredients to the original AREDS formula could improve on its roughly 25% reduction in progression risk. Substituting lutein and zeaxanthin for beta-carotene removed the lung cancer signal seen in smokers without any loss of efficacy, so the AREDS2 formula (vitamin C, vitamin E, zinc, copper, lutein, and zeaxanthin) replaced the original regimen for current and former smokers. A separate arm tested added omega-3 fatty acids (DHA and EPA). Five-year progression to advanced AMD was nearly identical with or without the omega-3s, so fish oil earned no place in the regimen despite earlier observational data suggesting a protective effect.

Genetics

AMD has one of the strongest genetic architectures of any common ophthalmic disease. Genome-wide association studies (GWAS), visualized with the characteristic skyline-shaped Manhattan plot that plots statistical significance of gene associations across chromosomal position, have identified numerous risk loci. Cumulatively, 19 identified loci account for approximately 40% of AMD's heritability, leaving most of it still unexplained by currently known variants.

Of all the loci implicated, the CFH (Complement Factor H) locus carries the strongest single association with AMD heritability, identified through GWAS meta-analyses as its major genetic contributor. CFH encodes a regulator of the complement system's alternative pathway, which ties AMD pathogenesis to chronic low-grade inflammatory and complement-mediated processes in the retina. That same biology underlies the newer complement-inhibitor drugs used for geographic atrophy, covered on the anti-VEGF and dry AMD management page. ARMS2/HTRA1 is the other major locus often discussed alongside CFH, but it does not surpass CFH's contribution to heritability.

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