Where are photoreceptors located in the retina and which layer contains the ganglion cell axons forming the optic nerve?

• A. Photoreceptors reside primarily in the outer nuclear layer (with outer segments); ganglion cell axons run in the nerve fiber layer forming the optic nerve
• B. Photoreceptors in inner nuclear layer; ganglion axons form the optic nerve
• C. Photoreceptors in the nerve fiber layer; ganglion axons in the outer nuclear layer
• D. Photoreceptors in the ganglion cell layer; axons in the choroid

Answer: (A)

Photoreceptors are the light-detecting cells whose cell bodies reside in the outer nuclear layer, with their light-sensing outer segments extending toward the retinal pigment epithelium. The axons of the retinal ganglion cells run through the nerve fiber layer, where they bundle together to form the optic nerve. So the correct description places photoreceptors in the outer nuclear layer and identifies the layer containing the optic nerve–forming axons as the nerve fiber layer. The inner nuclear layer contains other neurons (bipolar, horizontal, amacrine), not photoreceptors, and the ganglion cell axons are not located there.