This, and the fibrous white sclera help to keep the shape of your eyeball. The blood vessels that run through the choroid carry food and oxygen to the cells of the eye. The retina lines the inside of the eyeball. This is the nerve layer of the eye.The cells of the retina react to light.They send messages to the brain through the optic nerve, making it possible for you to see.he blood vessels that run through the choroid carry food and oxygen to the cells of the eye. The retina lines the inside of the eyeball. This is the nerve layer of the eye. The cells of the retina react to light. They send messages to the brain through the optic nerve, making it possible for you to see.