Bruch's membrane

Bruch's membrane is the innermost layer of the choroid. It is also called the vitreous lamina, because of its glassy microscopic appearance. It is 2–4 μm thick.^[1]

Layers

Illustration of Buch's Membrane

Bruch's membrane consists of five layers (from inside to outside):^[1][2]

1. the basement membrane 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 of the choriocapillaris

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

Embryology

Bruch's membrane is present by midterm in fetal development as an elastic sheet.

Pathology

Bruch's membrane thickens with age, slowing the transport of metabolites. This may lead to the formation of drusen in age-related macular degeneration.^[3] There is also a buildup 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.

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.

Eponym

Bruch's membrane was named after the German anatomist Karl Wilhelm Ludwig Bruch.

References

1. 1 2 Lee, Christina J.; Vroom, Jonathan A.; Fishman, Harvey A.; Bent, Stacey F. (Mar 2006). "Determination of human lens capsule permeability and its feasibility as a replacement for Bruch's membrane". Biomaterials. 27 (8): 1670–1678. doi:10.1016/j.biomaterials.2005.09.008. PMID 16199085. 
2. ↑ eOptha website: Anatomy of Uvea by Parthopratim Dutta Majumder
3. ↑ Young R (Mar 1987). "Pathophysiology of age-related macular degeneration". Surv Ophthalmol. 31 (5): 291–306. doi:10.1016/0039-6257(87)90115-9. PMID 3299827. 

External links

• Pictures at National Eye Institute

Anatomy of the globe of the eye
Fibrous tunic (outer)	Sclera Episcleral layer Schlemm's canal Trabecular meshwork Cornea Limbus layers Epithelium Bowman's Stroma Dua's layer Descemet's Endothelium
Uvea/vascular tunic (middle)	Choroid Capillary lamina of choroid Bruch's membrane Sattler's layer Ciliary body Ciliary processes Ciliary muscle Pars plicata Pars plana Iris Stroma Pupil Iris dilator muscle Iris sphincter muscle
Retina (inner)	Layers Inner limiting membrane Nerve fiber layer Ganglion cell layer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer External limiting membrane Layer of rods and cones Retinal pigment epithelium Cells Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Retina ganglion cell (Midget cell, Parasol cell, Bistratified cell, Giant retina ganglion cells, Photosensitive ganglion cell) → Diencephalon: P cell, M cell, K cell, Muller glia Other Macula Foveola Fovea centralis Parafovea Perifovea Optic disc Optic cup Ora serrata
Anatomical regions of the eye	Anterior segment Adnexa Fibrous tunic Anterior chamber Aqueous humor Iris Posterior chamber Ciliary body Lens Capsule of lens Zonule of Zinn Posterior segment Vitreous chamber Vitreous humor Retina Choroid
Other	Keratocytes Ocular immune system Tapetum lucidum Eye care professional Eye disease Refractive error Accommodation Physiological Optics Visual perception