In a real eye, after light passes through the lens, it shines straight through the vitreous humor to the back of the eye. It receives blood from the retinal vessels in order to allow it to function correctly. The retina takes the light that it receives through the cornea, pupil, and lens, and changes it into nerve signals that the brain can understand. It processes the light with special cells called rods and cones. Rods are the ones working to check out the shape of your friend and how he's moving.
Cones are a little different because they sense color .
Cones need more light than rods do for them to work well - this explains why it's hard to see different colors in the dark. So when you see that your friend's got brown skin, brown hair, a red T-shirt, and blue jeans, it means your cones are processing the light to give your eyes all the color information. Sometimes the cornea, lens, and retina don't work perfectly as a team, and the image ends up at the wrong place at the back of the eye. Sometimes the image appears in front or in back of the retina, instead of right on it. The Nemours Foundation is a nonprofit organization devoted to children's health and is the largest physician practice delivering subspecialty pediatric care in the United States.