Which two layers of the retina form a barrier to the passage of molecules between choroid and retina?

• A. Bruch's membrane
• B. External limiting membrane
• C. Retinal nerve fiber layer
• D. Bruch's membrane and External limiting membrane

Answer: (D)

The question is about the outer diffusion barrier at the border between the choroid and the retina. Molecules moving from the choroidal vasculature into the neural retina encounter two key barriers: Bruch's membrane, which is the extracellular matrix separating the choroid from the retinal pigment epithelium, and the External limiting membrane, formed by tight junctions between Müller cells and photoreceptors. Bruch's membrane lies right at the choroid–retina interface, while the External limiting membrane lies at the boundary within the outer retina. Together they restrict the passage of molecules from the choroid into the retina, making them the two structures that form this barrier.