Why do �animals' eyes shine in the dark ?

Eyes that glow in the pitch-black night make for many a scary tale. Isnt it..??

"A lot of the animals we see, especially the ones that go out at night, have a special, reflective surface right behind their retinas". That light-reflecting surface, called the tapetum lucidum, helps animals see better in the dark. It is a crystalline layer. If even a tiny amount of light gets into their eyes, it gets reflected around inside their eyes so that they can see it. It also means their eyes reflect back light, so that if a light shines on them, the reflection from their eyes can be seen in the dark.

But why this Reflection..??

It is a well known fact that we are able to see things around us because, the light reflected from the objects enters the eyes and reach the photoreceptor, which helps in transmitting the information to the brain. Similarly it applies to animals. But sometimes the light doesn't hit the photoreceptor, so the tapetum lucidum (present in few animals) acts as a mirror to bounce it back for a second chance to hit the photoreceptor.

Animals which have tapetum lucidum.

A large number of animals have the tapetum lucidum, including deer, dogs, cats, cattle, horses and ferrets. Humans don't, and neither do some other primates. Squirrels, kangaroos and pigs don't have the tapeta, either.

Do all eyes glow in same colour..??

And not all eyes animals glow the same color. This is due to different substances � like riboflavin or zinc � in an animal's tapetum. Also, there are varying amounts of pigment within the retina, and that can affect the color. Age and other factors also can change the color, so even two dogs of the same species could have eyes that glow different colors.

Cats often have eyes that glow bright green.

Another interesting thing now..!!

Simple, have you ever noticed when you use a flash to take a photo, sometimes the eyes of the person in that photograph look red?
Yes yes..(you may know but may not be sure of the reason of why it is..)If that is the case then you should know it now..!!
That red-eye (in the photograph) is because the eyes reflect back the light, and since there are a lot of blood vessels on the retina, the reflection looks red.


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