Eye Size

O

Orleander

OH JOY!!!!
Valued Senior Member
They have a squid with eyes the size of soccer balls. Why does it need eyes so large in comparison to the rest of its body? I know its to see better at deep dark depths, but why can't it just have small really good eyes, like a cat?
 
Architeuthis is equipped with the largest eyes in the animal kingdom. A number of vertebrate animals are larger than Architeuthis, yet none have eyes of comparable size. At 25 cm in diameter, the eyes of Architeuthis are the size of a human head! Cephalopods are visual animals and are distinguished among invertebrates for their highly complex visual system.

The visual systems of cephalopods and vertebrates are an example of convergent evolution. This means both groups of animals see alike, but their ability to see evolved separately in each group. In fact, if we compare squid eyes to our own, we find remarkable similarity in the anatomy. Squid and people both have eyes with single lenses, pupils, irises and retinas. We can only guess at the light sensing capabilities of an eye with such an enormous retina

http://www.dogpile.com/clickserver/...23=0&40=dMYPiPnbJzw7BR7+OleINA==&_IceUrl=true
 
so its the retina that needs to be bigger, not the lens or the pupil? Why can't they just have a extra large retina in a small eye?
 
I think a bigger lens would gather more light, in addition to needing a large retina area. It must be very dark down there.
 
Orleander, the answer is in the article you quoted.
"It has a huge lens the size of an orange and captures an awful lot of light in the dark depths in which it hunts."
 
Isn't a cat capable of seeing in absolute dark? why doesn't it just have eyes similar to the cats eyes then. I think that's what orleander was asking too.
 
s0meguy said:
Isn't a cat capable of seeing in absolute dark? why doesn't it just have eyes similar to the cats eyes then. I think that's what orleander was asking too.
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Well first of all, no creatures can see in absolute dark.
Cats make use of moonlight, squids can't.
And not many wavelengths penetrate far beneath the surface.
Red light is absorbed first, then orange, yellow, green etc.
Blue light penetrates the furthest.
So water absorbs diffent wavelengths of light at different depths, this had an impact on how squid eyes evolved.

In short, cats and squids life in completely different environments regarding light. You can't compare them.
A squids eye-size is the result of it's environment. If it could have evolved the same effectiveness while staying small, it would have. Eyes, and associated brain-activity, consumes huge amounts of energy.
 
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you're right I'm being stupid, you always need some kind of light or sound to see. So what's different about the moons light that makes it so that we can't see it but cats can? Well we can but not as effectively as cats apparently.
 
s0meguy said:
you're right I'm being stupid, you always need some kind of light or sound to see. So what's different about the moons light that makes it so that we can't see it but cats can? Well we can but not as effectively as cats apparently.
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Cats have a reflective layer behind the retina. So the light that enters their eyes hits the retina, then reflects back and hits the retina again. This is way they can see so much better in dark conditions.
You might have heard about or seen eyeshine in cats or other animals, this is caused by the light reflecting back out of their eyes.
This makes them see better at night but impairs their vision in day light somewhat.
In addition they have far more rods (and fewer cones) than we have, again enhancing night vision.
 
For any given technology: larger size improves resolution, light gathering capacity, and chromatic aberration performance, in an optical sensing device.

The control is the necessity of paying for, constructing, and supporting (in all ways) the enlarging device. Costs increase faster than performance gain, after a certain "sweet spot".

Cats probably would have much larger eyes, if there were no increasing price to be paid for them. Apparently either the costs are much lower or the payoffs are much higher for a squid in the middle of the ocean.
 
and the whales that eat them don't have large eyes because they have echo location and don't need large eyes..right?
 
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