Glowing eyes
Silently the tiger crouches, its striped coat blending perfectly with
the evening shadows. A deer is coming! The tiger turns its head to
watch—and suddenly its eyes begin to glow with a strange light.
The tiger can’t really make its eyes glow. Its eyes are very much like
yours. They have a curving, transparent window called the cornea
[(kawr]{.smallcaps} nee uh) just in front of the dark spot at the
middle, and a built-in lens just behind the dark spot. The cornea and
the lens gather light and bend it, so that it reaches the back of the
eye.
But tigers, cats, dogs, and some other hunting animals need to see
clearly at night as well as by day. Their eyes have a mirrorlike layer
at the back. At night the layer catches the very dim light that comes in
and reflects it forward inside the eye. The reflected light helps the
animals to see.
Sometimes in a dim light a cat will turn its head and look at you from
just the right angle. Then you see the strange glow—the light
reflecting from the special layer in the cat’s eyes.
