Bruch's membrane is the innermost layer of the choroid

Choroid

The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye , while in the outlying areas it narrows to 0.1 mm...

. It is also called the vitreous lamina, because of its glassy microscopic appearance.
It is 2–4 μm thick.

Layers

Bruch's membrane consists of five layers (from inside to outside):

1. the basement membrane
   Basement membrane
   The basement membrane is a thin sheet of fibers that underlies the epithelium, which lines the cavities and surfaces of organs including skin, or the endothelium, which lines the interior surface of blood vessels.- Composition :...
   
    of the retinal pigment epithelium
2. the inner collagenous zone
3. a central band of elastic fibers
4. the outer collagenous zone
5. the basement membrane
   Basement membrane
   The basement membrane is a thin sheet of fibers that underlies the epithelium, which lines the cavities and surfaces of organs including skin, or the endothelium, which lines the interior surface of blood vessels.- Composition :...
   
    of the choriocapillaris

The retinal pigment epithelium transports metabolic waste from the photoreceptors across Bruch's membrane to the choroid.

Pathology

Bruch's membrane thickens with age slowing the transport of metabolites. This may lead to the formation of drusen

Drusen

Drusen 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 drusen is normal with advancing age, and most people over 40 have some hard 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, primarily consisting of phospholipids. The accumulation of lipids appears to be greater in the central fundus than in the periphery. 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

Macular degeneration

Age-related macular degeneration is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults...

.

Pseudoxanthoma elasticum

Pseudoxanthoma elasticum

Pseudoxanthoma elasticum , also known as Grönblad–Strandberg syndrome, is a genetic disease that causes fragmentation and mineralization of elastic fibers in some tissues. The most common problems arise in the skin and eyes, and later in blood vessels in the form of premature atherosclerosis...

, myopia

Myopia

Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...

 and trauma can also cause defects in Bruch's membrane which may lead to choroidal neovascularization

Choroid

The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye , while in the outlying areas it narrows to 0.1 mm...

. 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.

External links

• Pictures at National Eye Institute
  National Eye Institute
  The National Eye Institute is one of the US National Institutes of Health that was established in 1968. The mission of NEI is to prolong and protect the vision of the American people. The NEI conducts and performs research into treating and preventing diseases affecting the eye or vision....