Drusen, from the German word for node or geode (the singular form is "Druse"), are small yellow or white collections of material that form between Bruch's membrane and the retinal pigment epithelium in the eye. It is normal for a few small ("hard") drusen to appear as people age, and most individuals over 40 years old 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 (AMD).

Classification

Drusen linked to aging and macular degeneration are different from optic disc drusen, which appear on the optic nerve head. Both types of drusen can be seen during an eye exam called ophthalmoscopy. Special imaging scans of the head or orbits, showing calcifications at the front of the optic nerve without changes in eye size, may indicate drusen in middle-aged or elderly individuals.

It is not known whether drusen cause macular degeneration or are signs of another process that also leads to drusen and macular degeneration. However, drusen are signs of a higher risk for complications from macular degeneration.

Hard drusen can join together to form soft drusen, which is a sign of macular degeneration.

Pathophysiology

Around 1850, three authors—Carl Wedl, Franciscus Donders, and Heinrich Müller—used different names for drusen. Drusen, the main feature of AMD, were first described in 1854 by Wedl. Wedl called them "colloid bodies of the choroid" and believed they were cells that did not form properly. Donders later referred to them as "Colloidkugeln," which means "colloid spheres" in German. Heinrich Müller named them after the German word for "geode," because of their shiny appearance. He thought drusen came from the nuclei of pigment cells in the choroid. Because drusen are located between the retinal pigment epithelium (RPE) and the choriocapillaris (the blood supply of the RPE), they might take away oxygen and nutrients from the RPE and photoreceptor cells. In some cases, drusen form above the "pillars" of the choriocapillaris, which is the area between two tiny blood vessels. However, differences are seen among different types of AMD.

The source of the proteins and lipids in drusen is not clear, but both the RPE and the choroid may contribute. Small amounts of several elements are found in drusen, with zinc being the most concentrated. The proteins in drusen include apolipoproteins and oxidized proteins, likely from blood, RPE, and photoreceptors. Drusen also contain parts of the complement system. Zinc in drusen may help form drusen by causing substances in the complement system, like complement factor H, to clump together and stop working.

Because drusen contain molecules that control inflammation, some researchers believe these deposits are created by the immune system.

Diagnosis

Drusen often do not cause symptoms and are often discovered during regular eye checkups when the eyes are examined with dilated pupils.

Treatment

Laser treatment for drusen has been studied. Although this method can remove drusen, studies have found that it does not lower the chance of developing choroidal neovascularisation, which causes blindness linked to age-related macular degeneration.