Light that strikes the depressed area at the center of the retina is perceived more sharply then light that falls out side the depression. The result is an image that appears focused at the center but blurred around the edges. A camera, however, can generate a photograph that is sharp from foreground to background and edge to edge. This explains why a photograph of a scene can be evenly focused throughout, even though your eye didn’t perceive the scene that way.
Adapted from Composition by Blue Fier (Photo Workshop, 2007; $30)