在线词典

Just how much of that clear vista can you take in anyway? If your eyesight is good, you probably think everything you see is always in sharp focus, like a photograph. This isn't the case. To understand why, let's take a closer look at your eye. The back of your eye is covered with light sensitive cells which send messages about what you see to your brain. The cells are not evenly distributed, however. At the center is a dense cluster of ultra-sensitive vision cells. Outside this central area, the cells rapidly become more sparse. These outer cells, responsible for peripheral vision, are great at detecting motion, but not so good at forming a clear image.