26.1 Features
Age-related macular degeneration (AMD) is a degenerative disorder of the choroid and outer retina, and the most common cause of blindness in those over the age of 50 in developed countries. AMD falls into two categories: atrophic (dry) and neovascular (wet). It is estimated that 15 million North Americans have some degree of dry AMD (accounting for 85–90% of AMD patients in North America). The most agreed upon risk factor is age, with studies demonstrating an increased prevalence in those 65 years or older. To a lesser degree, other factors include family history, race, female sex, light iris color, cigarette smoking, and medical conditions such as hypertension, hypercholesteremia, and cardiovascular disease. Furthermore, multiple genes involving collagen matrix production, the complement cascade, and lipid metabolism and transport are implicated.
In AMD, a lipid material, rich in apolipoprotein B, accumulates anterior to Bruch’s membrane. These lipid aggregations fall into two broad categories: drusen and basal deposits. Drusen are subdivided into typical and subretinal drusen/pseudodrusen. Basal deposits are further categorized as basal linear and basal laminar deposits. Typical drusen are focal collections between the retinal pigmented epithelial (RPE) basal lamina and inner collagenous layer of Bruch’s membrane. Subretinal drusen exist in the subretinal space, above the RPE. Neither basal linear nor laminar deposits are visible on fundus examination.
There are several changes in the RPE associated with AMD, including focal areas of hypopigmentation, hyperpigmentation, and atrophy that are visible on examination. Pigmentary changes of the RPE are considered secondary to RPE migration, with hyperpigmentary changes generally preceding hypopigmentary changes. Atrophy appears late in the disease process and is thought to occur where drusen regress with corresponding areas of death of the overlying RPE and retina and thinning of the underlying choriocapillaris.
Dry AMD can be classified as early, intermediate, or advanced. Early dry AMD consists of small or a few medium-sized drusen. Intermediate AMD is defined by more than 20 intermediate indistinct drusen, or 50 distinct drusen, or at least one large drusen, and/or the presence of nonfoveal involving atrophy (▶ Fig. 26.1, ▶ Fig. 26.2). Advanced AMD consists of foveal involving atrophy, or in the case of neovascular AMD, a choroidal neovascular membrane (▶ Fig. 26.3). Atrophy commonly spares the fovea until the later stages of the diseases.
Fig. 26.1 (a) Fundus photograph of the right eye depicting intermediate age-related macular degeneration (AMD), with many intermediate and large drusen without geographic atrophy. (b) Fundus photograph of the left eye depicting advanced AMD, with many intermediate and large drusen with geographic atrophy. (c) Optical coherence tomography (OCT) through the areas of drusen showing subretinal pigment epithelium collections without fluid or atrophy. (d) OCT through the areas of drusen showing subretinal pigment epithelium collections with additional areas of RPE atrophy and outer retinal atrophy.
Fig. 26.2 (a) Retinal pigment epithelium map showing elevations corresponding to drusen location and height. (b) Corresponding optical coherence tomography demonstrating significant drusen burden without evidence of fluid.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
