Is the outer BRB formed by tight junctions of the RPE on its apical or basal side?

Is the outer BRB formed by tight junctions of the RPE on its apical or basal side?

• A. Apical RPE
• B. Basal RPE
• C. Both
• D. Neither

Answer: (A)

The outer blood-retinal barrier is formed by tight junctions between adjacent RPE cells at their apical membrane, facing the subretinal space where photoreceptors reside. These apical junctions seal the paracellular path between the retina and the choroid, preventing diffusion from choroidal blood into the retinal environment while still allowing selective transport through the RPE itself. The basal side of the RPE lies against Bruch’s membrane toward the choroid, where tight junctions do not create the BRB. The inner BRB, by contrast, is provided by tight junctions between retinal capillary endothelial cells.

The outer blood-retinal barrier is formed by tight junctions between adjacent RPE cells at their apical membrane, facing the subretinal space where photoreceptors reside. These apical junctions seal the paracellular path between the retina and the choroid, preventing diffusion from choroidal blood into the retinal environment while still allowing selective transport through the RPE itself. The basal side of the RPE lies against Bruch’s membrane toward the choroid, where tight junctions do not create the BRB. The inner BRB, by contrast, is provided by tight junctions between retinal capillary endothelial cells.