AMD Clinical Features & Classification

Pathoanatomy

Age-related macular degeneration centers on the macula, and more precisely on the retinal pigment epithelium (RPE) and Bruch's membrane, the two-layer interface between the neurosensory retina and the underlying choroid. Nearly every clinical finding in AMD, from drusen to geographic atrophy to choroidal neovascularization (CNV), traces back to dysfunction at this RPE-Bruch's interface.

The early stages, before vision loss becomes significant, are sometimes grouped under the older term age-related maculopathy (ARM): drusen and RPE changes that precede the more advanced dry (atrophic) or wet (neovascular) forms.

Drusen

Drusen are yellowish deposits of extracellular material (lipids, proteins, and cellular debris) that accumulate between the RPE basement membrane and Bruch's membrane. They are the hallmark early finding of AMD, and their morphology carries real prognostic weight.

Hard vs. Soft Drusen

Small, hard (calcified) drusen are discrete, sharply defined, and carry a comparatively low short-term risk of progression. Large, soft, confluent drusen are the higher-risk lesion. Pale and poorly demarcated, they coalesce over time, and this morphology is the hallmark precursor to both choroidal neovascularization and geographic atrophy. Soft drusen are therefore the finding that most warrants closer monitoring intervals.

Dry AMD & Geographic Atrophy

Dry (non-neovascular) AMD progresses from scattered drusen toward its end-stage manifestation, geographic atrophy (GA): demarcated zones of RPE and photoreceptor atrophy. Clinically, GA appears as a sharply demarcated, hypopigmented or grayish area at the macula. Loss of the RPE and overlying photoreceptors, and in advanced cases the underlying choriocapillaris, leaves the larger choroidal vessels more visible through the atrophic zone. GA is the advanced stage of dry AMD and causes progressive, irreversible central visual impairment.

Wet AMD & Its Features

Wet (neovascular/exudative) AMD develops when choroidal neovascularization (CNV), new vessels growing out of the choroid, through Bruch's membrane, and into or beneath the retina, causes bleeding or fluid leakage. This is the process that converts dry AMD into wet AMD, and on exam it is subretinal fluid or blood, not drusen alone, that marks the transition.

A pigment epithelial detachment (PED) in an older patient often indicates underlying choroidal neovascularization, since a CNV membrane is commonly present beneath it. Left untreated, CNV can progress to a disciform scar: a subretinal fibrovascular scar representing the end-stage fibrotic result of chronic CNV. In up to 50% of Asian patients, the neovascular AMD variant is specifically polypoidal choroidal vasculopathy (PCV), a distinct CNV subtype with that regional predominance.

Large, highly elevated vascularized PEDs carry their own specific risk once anti-VEGF treatment starts: a retinal pigment epithelium (RPE) tear. The RPE separates from Bruch's membrane and retracts, exposing bare choroid underneath, usually within the first one or two injections. Visual outcomes after a tear are often poor, especially when the tear extends under the fovea. Patients with this PED morphology need counseling on that risk before treatment begins.

Symptomatically, the hallmark of wet AMD is sudden central distortion (metamorphopsia), rather than the gradual, painless peripheral field loss or slow central scotoma more typical of dry disease progression. In a patient with known drusen, new-onset metamorphopsia should be treated as a red flag for conversion to wet AMD and prompts urgent OCT. Regardless of form, AMD's central vision loss spares peripheral vision, which is preserved until the disease's end stages: a distinction worth explaining to patients worried about total blindness.

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