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


Seeing Is Believing Objects become visible when light refl ects off of them. Yet it takes more than capturing refl ected light to see an image. Eyes also have to bend the light. Here’s how: Light fi rst hits the cornea, or the clear covering on the front of the eyeball. Light refracts as it moves through the cornea. Behind the cornea is the iris, or the colored


part of the eye. T e iris has muscles attached to it that change its size. T is allows the iris to control how much light goes through the pupil, the dark center of the eye. Light then moves through the eye’s lens,


refracting more. Muscles attached to the lens change the lens’ shape depending on the distance to the object. Changing the lens’ shape refracts the light a little more or less. Because of how light travels through the lens, the retina receives the light from the object as reversed and upside down! T e retina then transmits the nerve signals to the brain, and the brain “sees” the object right side up.


Out of Focus Not all eyes are perfect, though. T e overall shape of the eyeball determines if light focuses on the retina or somewhere else. T at means a person will have problems focusing on an object if his or her eyeballs aren’t round. If an eyeball is long like a football, for


example, the light focuses before it reaches the retina. T is kind of eye has trouble seeing objects that are far away—a condition called nearsightedness. If an eyeball is too short, the light focuses past the retina. T en it’s harder to see objects that are closeup. T is is called farsightedness. In both cases, a pair of eyeglasses or contact


lenses are the answer. T ey refract the light a bit more or less, so that the light focuses on the retina. T en the image will be clear. Some animals, such as hawks have keen


vision and can see great distances. Other animals, such as moles, have poor vision and rely heavily on other senses.


cornea iris muscle blood vessels retina


pupil lens optic nerve JANUARY–FEBRUARY 2016 13


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