Which layer is the third in Bruch's membrane?

• A. Outer Collagenous Layer
• B. Elastic Layer
• C. Inner Collagenous Layer
• D. Basement Membrane of the RPE

Answer: (B)

Bruch's membrane is a five-layer barrier between the retinal pigment epithelium (RPE) and the choroid, arranged from the RPE toward the choroid as: the basement membrane of the RPE, the inner collagenous layer, the elastic layer, the outer collagenous layer, and finally the basement membrane of the choroid. The third layer from the RPE side is the elastic layer, which contains elastic fibers that give Bruch's membrane its characteristic elasticity. This middle layer helps maintain the proper spacing and diffusion pathway for nutrients and waste between the choroid and the outer retina, while the surrounding collagenous layers provide structural strength. Changes with age can involve this elastic layer, contributing to thickening or diffusion impairment of Bruch's membrane.