Eyes and Vision

The eye is the organ that lets you see. Your two eyes work together to turn light into pictures inside your brain. Vision is the sense that comes from this work. Most of what humans learn about the world arrives through the eyes.

Light is the key. Your eyes do not shoot anything out. They take light in. Light bounces off objects around you and enters your eye through a clear front window called the cornea. The cornea bends the light and sends it through a small hole called the pupil. The pupil is the black circle in the middle of your eye. It looks black because it is an opening, like the doorway of a dark room.

A ring of muscle called the iris controls how big the pupil gets. The iris is the colored part of your eye. In bright light, the iris makes the pupil small to let in less light. In a dark room, the pupil opens wide to catch more light. Your eye color comes from the iris, and no two people share exactly the same pattern.

Behind the pupil sits the lens. The lens focuses light onto the back of the eye, called the retina. The retina is packed with about 120 million tiny cells that react to light. Some of these cells, called rods, work in dim light. Others, called cones, see color. The retina turns light into electrical signals.

Those signals travel down the optic nerve, a thick bundle of nerve fibers, to the back of your brain. Your brain does the rest. The image that lands on your retina is actually upside down. Your brain flips it right-side up so the world makes sense. Seeing is really brain work as much as eye work.

About one in three people cannot see clearly without help. If your eyeball is shaped a little long, faraway things look blurry. If it is shaped a little short, close things look blurry. Glasses and contact lenses bend the light before it enters the eye, so the picture lands in the right spot on the retina.

Many animals see the world differently than you do. Eagles can spot a rabbit from a mile away. Dogs see fewer colors than humans. Bees see a kind of light called ultraviolet, which makes flowers look like glowing landing pads. Your eyes are amazing, but they show you only one slice of what is really out there.