How do inner and outer retinal blood supplies differ?

• A. Inner retina relies on choroidal circulation
• B. Inner retina is avascular; outer retina supplied by retinal arteries
• C. Inner retina is supplied by retinal arteries; outer retina is avascular and relies on the choroidal circulation
• D. Outer retina supplied by ciliary body arteries

Answer: (C)

The retina has two separate blood supplies: the inner retina is nourished by the retinal arteries, while the outer retina depends on the choroidal circulation. The central retinal artery branches form capillary networks that feed the inner layers, including the nerve fiber, ganglion cell, and inner nuclear layers. The outer retina, including the photoreceptors, has no retinal vessels and relies on the choriocapillaris in the choroid for oxygen and nutrients, with diffusion across the retinal pigment epithelium to reach the photoreceptors. This arrangement fits the high metabolic needs of the photoreceptors and explains why diseases affecting the choroid can impact the outer retina. Arteries from the ciliary body do not directly supply the outer retina.