Eyes are complex globe-shaped organs about the size of ping-pong balls. They are part of the visual system. The human eye works much like a digital camera, focusing incoming light on bringing us the clear pictures we see from the moment we wake up to the moment we go to sleep.
The whole eye is protected by the eyelid, which frequently closes (blinks) to keep the eyeball moist and clean. The cornea, a clear dome-like structure, covers the iris and the pupil and is responsible for directing and focusing light rays, providing us with sharp vision.
The iris is the colorful part of the eye and has a critical job—it has muscles that that change its shape, allowing it control of how much light goes through the pupil (the black circle in the middle of the iris). Other parts of the eye include the lens and the retina which work together to project the image and send it to the brain to process.
The complexity of eyes varies in different animals, from the simplest—detecting light and dark—to the most complex—distinguishing shapes and colors—like the human eye.