Forgotten in its old age

by Aditya

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Multiple sources on the internet (including answers on this site) claim that red-eye is created by light from the flash reflecting on the blood vessels in back of the eye.

So, why do animals like dogs, that I believe also have red blood (I'm not going to injure my dog in order to test this, but I'm pretty sure the blood is red) have green-eye?

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Maybe some sort of vegetation growing on the back of pet's eyes reflecting the light? –  Nir May 2 '11 at 13:35
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...and lets not forget Riddick –  Jakub May 2 '11 at 15:24
    
+1 for not injuring your dog. (Also, good question :P) –  poke May 2 '11 at 17:59

2 Answers 2

up vote 20 down vote accepted

Many animals, including cats and dogs, have a reflective layer of cells at the back of the eye called the tapetum lucidum ('the tapestry of clarity'). This reflects the light back through the light-sensitive cells in the retina for a 'second pass', allowing the animal to see better at night.

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You don't have to do photography to notice this green reflective layer; staring into a cat's eye at exactly the right angle will let you see that at naked eye :) –  badp May 2 '11 at 18:17
    
Yup, headlights are particularly effective at showing them up. –  ElendilTheTall May 2 '11 at 18:49
    
Nice answer, +1, but no one as yet has explained why the color is green specifically... –  Uticensis May 2 '11 at 20:47
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@billare: actually, eyeshine can be white, green, blue, yellow or pink, depending on the angle you view it at. –  ElendilTheTall May 2 '11 at 20:57

According to Wikipedia it seems that animals that exhibit this phenomenon ("eyeshine") have an extra layer of tissue within their eyes that cause light to be reflected in a different way.

enter image description here
Source: Wikipedia

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Wikipedia has a picture of a cat which dramatically illustrates red eye and "eyeshine" occurring simultaneously. –  mattdm May 2 '11 at 14:03

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