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Birds of prey, such as this falcon, can spot a rabbit from far away.


Seeing is Believing Objects become visible when light bounces off of them. Yet it takes more than catching light to see an image. Eyes also have to bend the light. Here’s how: First, light hits the cornea. T at’s the clear covering on the front of the eyeball. T e cornea refracts, or bends, the light. T is helps the eye focus. Behind the cornea is the iris. T at’s the


colored part of the eye. T e iris has muscles attached to it that change its shape. T is allows the iris to control how much light goes through the pupil, the dark center of the eye. T e light passes through the pupil to reach


the eye’s lens. T e lens’ job is to focus light rays on the back of the eyeball. T e light goes to a part of the eye called the retina. T e lens helps form an image on the retina,


but the image looks a little odd. It’s reversed and upside down! T e retina has to transmit the image to the brain, and the brain “sees” it right side up.


Out of Focus? Not all eyes are perfect, though. T e shape of the eyeball determines where light hits the retina. T at means a person will have problems focusing on an object if his or her eyeballs have an unusual shape. If an eyeball is too long, for example, the


light focuses before it reaches the retina. T is kind of eye will have trouble seeing objects that are far away. T is is called nearsightenedness. If an eyeball is too short, the light focuses


past the retina. Now it’s harder to see objects that are close-up. T is is called farsightedness. In both cases, a pair of eyeglasses or contact


lenses are the answer! T ey will correct the vision so that the light hits the retina in the right place. T en the image will be clear. Some animals, like hawks and falcons, have


keen vision and can see great distances. Other animals, like rhinoceroses and moles, have poor vision. T ese animals must rely on other senses to help them survive.


cornea iris muscle blood vessels retina


pupil lens optic nerve JANUARY–FEBRUARY 2016 19


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