Dr Karl on cats seeing in the dark
Dr Karl Kruszelnicki is the smartest human in Australia and knows lots of things about science.
He has a weekly show on talk back science on radio, a regular segment on breakfast television about science, has written numerous books on science, and has a regular column in Melbourne's The Age and the Sydney Morning Herald Saturday magazines, GOOD WEEKEND called 'mythconceptions'.
Last Saturday, Dr Karl wrote 'Claws and effect' about cat's seeing at night. He said that I can share this on my blog with you (my human asked him if it was okay). Note that this was written from the human perspective.
[A] bold claim about cats is that they can see in the dark. The truth is that they cannot see in absolute darkness any more than we can. However, they are much better adapted than humans for seeing in low levels of light.
To understand why cats see better in semi-darkness, we need to know that rods and cones are the main cells that turn incoming light into electrical signals. Rods are more sensitive and work better in low-light situations, while cones are less sensitive and work better when there's lots of light. A cat's eye is much more richly endowed with rods than a human's eye.
Also cats have an extra layer in the back of the eye behind the retina, which means that the incoming light has two chances to hit the rods. This layer is called the tapetum lucidum. It's made from 15 types of cells and is very reflective. It glows a silvery-greeny-golden colour in most cats, but can be ruby-red in Siamese cats. The incoming light enters the front of the eye and passes through the transparent innards of the eye and enters the retina. At this stage, the light will register if it hits a rod. In the human eye, if it misses, the light is absorbed in a black layer behind the retina and is gone forever. But in the cat eye, if the light has not hit a rod, it will reflect off the tapetum and be bounced forward. The light now has a second chance to hit a rod and be registered.
So when you shine a very bright light (such as a camera flash) into a human eye, you get a reddish colour, from the blood vessels that nourish the retina. These blood vessels are in front of the retina, so they light up as well. When you shine a bright light (such as a torch or car headlights) into the eyes of a cat at night, you see a reflection of that light thanks to the tiny "mirror" in the back of the cat's eye.
All about Dr Karl
Dr Karl is not only really smart, he is also modest and very funny. Although my human can't understand his jokes.
Dr Karl (having coffee with my human in June 2005)
*As always, please check out Cooper and Camilla who always have interesting things to say.
........ooooooooOOOOOOOOoooooooo........
Last night we watched Psycho Beach Party (don't let the price fool you, if you can get it for A$4.99 like we can in Australia). It was so bad that it was quite good and pretty funny.
I didn't feel like dinner tonight. All I want to do is to sit on my human's lap. In fact, I insisted he sit on my chair while I sit on his lap to use the computer (but that means he gets impatient and looks over my shoulder at my typos).
I did have a bigger breakfast than usual though. I had the middle bit of a chicken wing and also a big slice of ham. Boy was I hungry this morning, but now I'm not.
keisercat@wildmail.com
He has a weekly show on talk back science on radio, a regular segment on breakfast television about science, has written numerous books on science, and has a regular column in Melbourne's The Age and the Sydney Morning Herald Saturday magazines, GOOD WEEKEND called 'mythconceptions'.
Last Saturday, Dr Karl wrote 'Claws and effect' about cat's seeing at night. He said that I can share this on my blog with you (my human asked him if it was okay). Note that this was written from the human perspective.
[A] bold claim about cats is that they can see in the dark. The truth is that they cannot see in absolute darkness any more than we can. However, they are much better adapted than humans for seeing in low levels of light.
To understand why cats see better in semi-darkness, we need to know that rods and cones are the main cells that turn incoming light into electrical signals. Rods are more sensitive and work better in low-light situations, while cones are less sensitive and work better when there's lots of light. A cat's eye is much more richly endowed with rods than a human's eye.
Also cats have an extra layer in the back of the eye behind the retina, which means that the incoming light has two chances to hit the rods. This layer is called the tapetum lucidum. It's made from 15 types of cells and is very reflective. It glows a silvery-greeny-golden colour in most cats, but can be ruby-red in Siamese cats. The incoming light enters the front of the eye and passes through the transparent innards of the eye and enters the retina. At this stage, the light will register if it hits a rod. In the human eye, if it misses, the light is absorbed in a black layer behind the retina and is gone forever. But in the cat eye, if the light has not hit a rod, it will reflect off the tapetum and be bounced forward. The light now has a second chance to hit a rod and be registered.
So when you shine a very bright light (such as a camera flash) into a human eye, you get a reddish colour, from the blood vessels that nourish the retina. These blood vessels are in front of the retina, so they light up as well. When you shine a bright light (such as a torch or car headlights) into the eyes of a cat at night, you see a reflection of that light thanks to the tiny "mirror" in the back of the cat's eye.
All about Dr Karl
Dr Karl is not only really smart, he is also modest and very funny. Although my human can't understand his jokes.
Dr Karl (having coffee with my human in June 2005)
*As always, please check out Cooper and Camilla who always have interesting things to say.
........ooooooooOOOOOOOOoooooooo........
Last night we watched Psycho Beach Party (don't let the price fool you, if you can get it for A$4.99 like we can in Australia). It was so bad that it was quite good and pretty funny.
I didn't feel like dinner tonight. All I want to do is to sit on my human's lap. In fact, I insisted he sit on my chair while I sit on his lap to use the computer (but that means he gets impatient and looks over my shoulder at my typos).
I did have a bigger breakfast than usual though. I had the middle bit of a chicken wing and also a big slice of ham. Boy was I hungry this morning, but now I'm not.
keisercat@wildmail.com
posted by Keiser at 20:30
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