Drusen are tiny yellow or white
accumulations of extracellular material that build up between Bruch’s membrane
and the retinal pigment epithelium of the eye. The presence of a few small
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.
Classification Drusen are 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. Optical coherence
tomography scans of the orbits or head, calcification at the head of the optic
nerve without change in size of globe strongly suggests drusen in a middle-age
or elderly patient. 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. ‘Hard drusen’ may coalesce into ‘soft
drusen’ which is a manifestation of macular degeneration.
Pathophysiology Drusen were initially described by
Franciscus Donders who called them “Colloidkugeln”. Later, Heinrich Müller
named them for the German word for geode, based on their glittering
appearance. In view of their location between the retinal pigment epithelium
and its vascular supply, the choriocapillaris, it is possible that
drusen deprive the RPE and photoreceptor cells 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. See also
Optic disc drusen Notes
External links agingeye.com
image from macular.org