Which statement about retinal blood supply is correct?

• A. The inner retina is supplied by the choroidal circulation
• B. The outer retina is supplied by the retinal arteries
• C. The optic nerve head receives its blood supply from the retinal circulation
• D. Outer retina is avascular and relies on the choroidal circulation

Answer: (D)

The key idea is how the retina gets its blood supply from two separate vascular systems. The inner retina is nourished by the retinal circulation, derived from the central retinal artery. In contrast, the outer retina, which includes the photoreceptors, is avascular and relies on the choroidal circulation—specifically the choriocapillaris—for oxygen and nutrients by diffusion from the underlying choroid. The optic nerve head is primarily supplied by the short posterior ciliary arteries feeding the choroidal circulation around the nerve, not by the retinal circulation. So the statement that the outer retina is avascular and relies on the choroidal circulation is the correct one.