June 23, 2003
A: FROM MENTOR DESIREE BUTTER IN PA
Abi,
You can find out more about cat vision at:
http://videoforcats.com/catvision.htm
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A: FROM MENTOR AMY MCMILLAN IN NY
Hi Abi, Good question. Nocturnal animals do have a more dense array of rods
than do the human eye. These rods contain a light-absorbing pigment called
rhodopsin, which will break down in bright light so many animals with good
night vision don't see well during the day. There are other adaptations to
dark vision including larger eyes and a reflective membrane that serves to
mirror any light that is present. This website is a nice summary of all the
ways nocturnal animals deal with sight
http://ebiomedia.com/gall/eyes/nocturnal.html.

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A: FROM MENTOR JOAN LUSK IN RI
Cats do have more rods, relative to humans. Their pupils can open
wider, too, admitting more light. And each photon has two chances to
trigger a reaction, because the reflective membrane behind a cat's
retina sends those that missed hitting a receptor the first time back
through the retina for a second try. If it misses again, the photon
come back out through the pupil and we see the reflected light. Many
animals that are active at night have such membrane - think of deer
caught in the headlights and other animals you've seen cross the road
at night. How weird it would be if people's eyes reflected light
like that! Here's a light-hearted site:

http://videoforcats.com/catvision.htm