Slowly progressive atrophy of macular retinal pigment epithelial cells (the RPE cells lie under the light sensitive neuro retina).
Retina image of dry AMD
Source: www.retinagallery.com
New choroidal blood vessels grow into and under the retina. These bleed or leak fluid, causing macular oedema and scarring. Less common than dry AMD, but usually more severe.
Retina image of wet AMD
Source: www.retinagallery.com