True or False?
An ostrich’s eye is bigger than its brain. Tat’s true. Pigeons have fantastic color vision. Tat’s also true. Most hamsters only blink one eye at a time. True. Dolphins can move each eye independently and can process two different images at once. True again. Geckos can see colors around 350 times better than a human, even in dim lighting. Also true! Animals depend on their eyes to help them
make sense of the world around them. Animal eyes come in many shapes, sizes, colors, and even numbers. Yet they all do the same job— collect light. Te light stimulates nerve cells in the eye, the cells pass the signals on to the brain. With help from the brain, eyes turn light into sight. Human eyes work like those of other
animals, capturing light and transmitting the response to the brain. Sight provides an estimated two-thirds of all the information a human brain takes in. Te human eye is oſten compared to a
camera. Both have lenses that bend and focus light. Both have openings that can adjust to different levels of light. Te eye transmits a constant stream of images to the brain by electrical signals, just as a camera stores images. But the comparison ends there due to the complex nature of the eye.
EYES IN ACTION
In humans, the cornea, iris, pupil, and lens work together to focus light on the retina. The light-sensitive retina lines much of the eyeball. Light stimulates nerve cells on the retina and the resulting nerve impulses travel along the optic nerve to the brain. There, the brain interprets the impulses as color, motion, shape, or other features.
12 NATIONAL GEOGRAPHIC EXTREME EXPLORER pupil
Light Moves Light is a form of energy, such as electricity or sound. It can come from natural sources, such as the sun, or artificial sources, such as a lamp or fire. Visible light is the light humans can see, but some other animals detect light waves invisible to us. Light travels faster than anything else in the
universe. It travels in waves and nearly straight lines. In space, it moves 299,700 kilometers per second, zipping from the sun to Earth in just over eight minutes! Once light reaches Earth, air, water, or glass slow it down, but just a bit. Light waves behave like other kinds of
waves. Light reflects, or bounces off objects. It also refracts, or bends, as it passes through different materials. And it can be absorbed, or taken in, by materials. Tese characteristics affect how and what
eyes see. For example, we call objects that absorb all of the light waves “black” while we call those that reflect all of the waves “white.”
iris iris
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