Cats' pupils perfect for night vision!
The eyes have it!! Cats eyes are special - anyone can tell you that.
For centuries man has looked into the eyes of a cat and seen something mysterious and exotic.
Looking into the eyes of a cat is something special
because the cat family has a pupil unlike any other animal kingdom.
Anyone who has accidentally frightened a cat hich was happily lying in the sun can attest to the dramatic transformation of which cats' eyes are capable.
Cat's pupils can rapidly change from barely detectable vertical slits,
into big black circles which sometimes seem to fill the entire startled feline's face.
It is in the arrangement of the iris muscles around the pupil itself
with its ability to change its pupils from a verical slit to a circle.
These muscles are actually arranged in a figure eight pattern.
This configuration allows the cats' pupil to open and close to a far greater extent than our own.
Of course, what this means is that the cat can open its eyes wider to let more light in, thus helping it to "see in the dark"
Cats do see some colours, but they have far fewer colour receptors than we do.
Consequently, they see their world far more in terms of shades of brightness,
rather than the shades of colour which characterize our world.
Again this feature is an adoptation to the need for night vision,
as there is less need for colour perception in dim light.
Another feature which helps the cats' excellent night vision is a structure called the "Tapetum Lucidum"
The tapetum is a mirror like structure which lines the back of the cats' retina.
The retina is the part of the eye which contains the cells which are actually sensative to light.
These cells pick up the light messages, transfer them to nerves, and thus give us the thing we call sight.
When dim light passes through the cells of the cats' retina, it is reflected on the tapetum lucidum and pases back through the retinal cells; thus giving them a double bite at it!
So although cats can't in fact see in total darkness, they can use available light 50% more effectively than we can and only need one sixth of the illumination we need to see!!
Next time you catch the unearthly glow of a cats' eye shining back at you in a narrow beam of torch light; don't think of aliens!!
Instead, spare a thought for the poor old "Tapetum Lucidum" working overtime!!
Catharina's poetry
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