Bruch's membrane is the innermost layer of the choroid.
Bruch's membrane consists of five layers:
- the basement membrane of the retinal pigment epithelium
- the inner collagenous zone
- a central band of elastic fibers
- the outer collagenous zone
- the basement membrane of the choriocapillaris
The retinal pigment epithelium transports metabolic waste from the photoreceptors across Bruch's membrane to the choroid.
Bruch's membrane thickens with age slowing the transport of metabolites. This may lead to the formation of drusen in age-related macular degeneration. There is also a build up of deposits (Basal Linear Deposits or BLinD and Basal Lamellar Deposits BLamD) on and within the membrane. This build up seems to fragment the membrane into a lamellar structure more like puff-pastry than a barrier. Inflammatory and neovascular mediators can then invite choroidal vessels to grow into and beyond the fragmented membrane. This neovascular membrane destroys the architecture of the outer retina and leads to sudden loss of central vision - wet age related macular degeneration.
Pseudoxanthoma elasticum, myopia and trauma can also cause defects in Bruch's membrane which may lead to choroidal neovascularization. Alport's Syndrome, a genetic disorder affecting the alpha(IV) collagen chains, can also lead to defects in the Bruch membrane such as 'dot and fleck' retinopathy.
Bruch's membrane was named after the German anatomist Karl Wilhelm Ludwig Bruch.