Age-related macular degeneration (ARMD) is an acquired degenerative disorder affecting the macula, with the hallmark being the presence of ‘drusen’ in the macula. There are two main subtypes, which we will describe in the following article.
ARMD is usually classified into two types: Dry ARMD (non-exudative, non-neovascular), and Wet ARMD (exudative, neovascular). The former makes up 90% of cases, whilst the latter is less common, however is associated with rapid progression to advanced vision loss. Another, temporal classification of the condition exists, where the disease is classified as ‘early’, ‘intermediate’, or ‘advanced’ ARMD.
A combination of genetic and environmental risk factors are thought to interact to modify the Bruch's membrane/choroid complex, the retinal pigment epithelium (RPE) and photoreceptor cells. Drusen, the main histopathological hallmark of the condition, are extracellular eosinophilic deposits located between the RPE and Bruch’s membrane, thought to be derived from immune-mediated and metabolic processes in the RPE. Age-related drusen are common after the 6th decade, but these are biochemically distinct from the drusen we see in ARMD.
<aside> 💡 ARMD is the most common cause of irreversible vision loss in the developed world.
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In the UK, significant visual impairment (binocularly 6/18 or worse) from AMD affects about 4% of the population aged over 75 years and 14% of those over 90.
Dry ARMD is also known as non-exudative, or non-neovascular ARMD. Vision declines over a period of months/years, usually in both eyes, however they may be asymmetrically affected. The main clinical sign is soft drusen. With progression, the end result of dry ARMD is geographic atrophy (GA): well circumscribed areas of RPE atrophy, with variable loss of the retina and choriocapillaris. OCT may show drusen: in addition to loss of RPE in geographic atrophy.
Fundus photographs at different stages of age-related macular degeneration (AMD) progression. (a) Large and intermediate drusen at intermediate stage of AMD. (b) Neovascular AMD—right eye with evidence of sub-retinal fluid, hemorrhage, and hard exudate in the presence of choroidal neovascularization. (c) Fluorescein angiography of the neovascular AMD—Left eye showing the hyperfluorescence of the fluorescein angiogram corresponding to the area of the choroidal neovascularization. (d) Central geographic atrophy—Right eye with evidence of geographic atrophy involving the center of the fovea with evidence of large drusen temporally. - Image Courtesy of Ratnapriya et al.