Which two structures create the blood-ocular barrier most significantly?

• A. Tight junctions in retinal capillary endothelium and tight junctions in RPE
• B. Gap junctions in photoreceptors and adherens junctions in choroid
• C. Tight junctions in corneal endothelium and desmosomes in sclera
• D. Fenestrated capillaries and gap junctions in the iris

Answer: (A)

The blood-ocular barrier mainly relies on sealing junctions that block paracellular diffusion between blood and ocular tissues. The inner barrier is formed by tight junctions in the retinal capillary endothelium, which line the retinal vessels and tightly seal the vessel walls. The outer barrier comes from tight junctions between retinal pigment epithelium (RPE) cells, which separate the neural retina from the choroid and regulate the movement of ions and fluids into the subretinal space. Together, these two tight-junction–rich layers establish the selective barriers that protect retinal homeostasis and function. Structures with gap junctions, adherens junctions, or desmosomes do not create this sealing effect, and fenestrated capillaries would actually promote permeability, not barrier formation; likewise, the corneal endothelium and sclera are not the primary components defining the blood-ocular barrier.