(singular, "druse") are tiny yellow or white accumulations of extracellular material that build up in Bruch's membrane
of the eye
. The presence of a few small ("hard") drusen is normal with advancing age, and most people over 40 have some hard drusen. However, the presence of larger and more numerous drusen in the macula
is a common early sign of age-related macular degeneration
Drusen associated with aging and macular degeneration are distinct from another clinical entity, optic disc drusen
, which is present on the optic nerve
head. Both age-related drusen and optic disc drusen can be observed by ophthalmoscopy
Whether drusen promote AMD or are symptomatic of an underlying process that causes both drusen and AMD is not known, but they are indicators of increased risk of the complications of AMD.
Drusen were initially described by Donders who named them for the German word for geode
, based on their glittering appearance. In view of their location between the retinal pigment epithelium
(RPE) and its vascular supply, the choriocapillaris
, it is possible that drusen deprive the RPE and photoreceptors
of oxygen and nutrients. Interestingly, drusen always develop above the so called pillars of choriocapillaris
that is the area between two microvessels.
The source of the proteins and lipids in drusen is also not clear, with potential contributions by both the RPE and the choroid. Several trace elements are present in drusen, probably the most concentrated being zinc. The protein composition of drusen includes apolipoproteins and members of the complement system. Zinc in drusen have been suggested to play a role in drusen formation by precipitating and inhibiting the elements of the complement cascade, especially complement factor H.
The presence of molecules that regulate inflammation in drusen has led some investigators to conclude that these deposits are product of the immune system.
- Donders F. Beitrage zur pathologischen Anatomie des Auges. Archiv Für Ophthalmologie 1854; 1:106-18