Eyes that Glow!

Have you ever had an experience of walking across a  forest during night and encountering glowing eyes that look at you …  or many times at home glowing eyes of your pets … why do some animals' eyes glow at night?
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.
A large number of animals have the tapetum lucidum, including deer, dogs, cats, cattle, horses and ferrets. Humans and some other primates and animals like  Squirrels, kangaroos and pigs don't have the reflective layer.
Not all eyes animals' glow the same color. Even then the color shades changes with age & two dogs of the same species could have eyes that glow different colors , due to different substances — like riboflavin or zinc. Cats often have eyes that glow bright green, though Siamese cats' eyes often glow bright yellow.
Alligators and crocodiles shine red. Such eyeshine is found in many other kinds of animals including various mammals, sharks, sturgeons, and some moths, but not in birds nor amphibians: and in all colors except violet and white.
When light enters the eye, it's supposed to hit a photoreceptor that transmits the information to the brain. But sometimes the light doesn't hit the photoreceptor, so the tapetum lucidum acts as a mirror to bounce it back for a second chance.
Most mammals, the pupil of the eye is round but in many of the flesh- eaters such as the domestic cat, it becomes a vertical slit in bright sunlight and widens to cover most of the pupil in darkness. That is why they see so well at night. In the eyes of the kangaroo and some hoofed animals, notably the goat, the pupil is a horizontal slit.


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