a PDF on Whale eyes (appears to be a children's textbook):
relevant info is on page 3 and 4
http://www.destinationcinema.com/our...ments/v3_3.pdf
quote from page 3:
Quote:
The vertebrate eye is like a camera that forms a
picture. The visual system transmits the image
in biochemical code to the brain via the optic
nerves. The human eye is similar to the eyes of
other mammals, whales included.
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and a really good explaination of the differences between squid and human eyes:
Quote:
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In humans (and in fact in all vertebrates) the inner layer of the optic cup forms the retina. This means the retina is actually "reversed", with the light-sensitive portion (the rods and cones) on the outside. IOW, incoming light has to pass through all of the layers before it reaches the rods and cones.
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This is where the idea that the layers provide protection against certain types of light from frying the rods and cones.
Quote:
In squid (and octopi and other molluscs), however, the eye is somewhat different. The light sensitive portion is on the inside surface, facing the incoming light. Light strikes the rods and cones before the other parts. This means that squid eyes have substantially greater light sensitivity than humans. The nerve fibers of the squid eye don't have to pass through the retina to enter the visual cortex of the brain, they are already on that side of it. By contrast, the neural elements of the vertebrate eye must pass through, and that's what makes the blind spot. Squid eyes have no blind spot.
In addition, squid eyes have a different focussing mechanism (using the lens rather than the cornea) that allows significantly greater function underwater by reducing refraction and eliminating the problems humans have with astigmatism, etc. Squid don't have to wear glasses...
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Does that help?