It was somewhat unclear in places, and has been replaced with what you've read above. It's still on this page because the above text has not been completed. It'd be vastly inefficient to do it the way nature does it, however, by throwing rays of light out from the sun and seeing if they hit our eye. A model of the human eye. First, let's look at the eye itself.
Light rays come in through the lens.
These rays hit the back of the eye, the retina, which is equipped to detect the photons hitting it. The image is reversed, but the brain corrects for this and then displays it properly. From a ray tracing perspective, this is interesting, but still somewhat difficult to model. Once again, we can't cast so many rays that we get enough coming through the lens. The screen is placed in front of the eye.