What Is Bruch's Membrane?

Bruch's membrane is a thin layer of tissue that serves as the inner layer of the choroid. It derives its name from a 19th-century German anatomist who first described it. This membrane has a glassy appearance when viewed with a microscope. Thus, it is sometimes called vitreous lamina, a Latin term that can be interpreted as "glass-like layer." Other alternate terms include lamina basalis and omplexus basalis.

The choroid is the layer of the eye comprised of blood vessels and the location of Bruch's membrane. Also known as the choroidea or choroid coat, it consists of four layers. Bruch's membrane is one of them, lying at the innermost area of the choroid. The outermost layer is Haller's layer, which is made up of blood vessels of comparatively large diameter. In between those two layers is Sattler's layer, which consists of blood vessels of mid-sized diameter as well as the choriocapillaris — named so because it consists of the smallest blood vessels, which are called capillaries.

Bruch's membrane in particular is about 2 to 4 micrometers thick. Its main function is to act as a barrier between the choroid and the retina, which is the tissue that lines the eye's inner surface. The specific part of the retina barred from the choroid is the retinal pigment epithelium (RPE), or pigmented layer of retina. The membrane also functions as a support system for the choroid. Bruch's membrane is divided into five parts, which consists of the RPE basement membrane, the inner collagenous zone, an elastic-fiber band at the center, the outer collagenous zone, and the choriocapillaris' basement membrane.

As a person gets older, the Bruch's membrane tends to thicken. Since the RPE has to pass through this layer to transport waste material to the choroid, the thickening can slow down such an activity. This could lead to small white or yellow deposits of extracellular material known as drusen accumulating on or in the Bruch's membrane. Macular degeneration, which is characterized by loss of central vision, consequently occurs. Physicians combat the condition with laser treatment or immunomodulatory agents.

Bruch's membrane is named after a German anatomist named Karl Wilhelm Ludwig Bruch, who lived between 1819 and 1884. In addition to the aforementioned eponym, the lymph nodes found in the mucous membrane covering the eye's white part — the palpebral conjunctiva — is named after him as they are sometimes called Bruch's glands. Bruch is also known to have taught anatomy and physiology at the University of Giessen in Germany and the University of Basel in Switzerland.