1 year, 5 months ago
Why do animal eyes glow in the dark when reached by light but human eyes don't?
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M$1 Answer
Some animals have a lining of reflective cells called Tapetum Lucidum in or behind the retina which helps produce this glowing effect.
According to,
http://www.inspirationline.com/Brainteaser/animaleyes.htm
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Human eyes do reflect light, as all flash photographers know ... they just don't do it very well. Our eyes look red in some photographs. But it's not a reflector. It's the camera flash bouncing off the red blood vessels and red tissue in the back of our eye. The distinctive "eyeshine" given off by wolves and raccoons and crocodiles, among many other species, comes from the "tapetum lucidum", a mirror-like layer of cells in or behind the retina. This structure is found mostly in nocturnal animals, for whom it serves as a kind of light amplifier. The retina captures some of the light that enters the eye, but some passes through. The tapetum lucidum bounces it back at the retina, giving the animal a second chance to "see" it. It's this ricocheting light that gives off the vaguely eerie glow we've come to associate with scary tales ... all those sinister pairs of eyes staring out from gloomy thickets.
How about human ability to see at night? Cats are much better adapted for performance under low light than we are. They have larger corneas and pupils than us to collect more light in dim conditions. They also have the tapetum which reflects light back out of the eye. This way, their retinae get two chances to capture each photon of light. A cat's tapetum reflect 130 times more light than the human eye. This is why cats' eyes glow in the dark in photographs
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According to Wikipedia,
http://en.wikipedia.org/wiki/Tapetum_lucidum
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The tapetum lucidum contributes to the superior night vision of some animals. Many of these animals are nocturnal, especially carnivores that hunt their prey at night, while others are deep sea animals. Although strepsirrhine primates have a tapetum lucidum, humans and other haplorhine primates do not.
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