Squid eye vs human eye


Feb 14, 2005
Hi all.

Has the squid eye developed "better" than the human eye? They don't have a "black spot" as I understand it. Is the design inherently better than with ours?
:welcome: maarek99

I have no informations on squid's visual acuity, but Hughes (1977) reported that the cuttlefish has a very high visual acuity, which is better than that of the cat (!!!) (cited in a paper by Schaeffel et al., 1999)...
Like many other aquatic and non-aquativ invertebrates, cephalopods are also sensitive to the polarization of light 'cos the microvilli within their retina have a special horizontal/vertical arrangement (e. g. see Shashar et al., 1996; Shashar et al., 2000 etc.).... My eyes are not very sensitive to polarized light :wink:, so regarding polarization of light the ceph-eyes are better than my human eyes...

Sorry, that's not quite an answer to your "black spot"-squid-question...

I don't know about all cephs, but some of them have the veins feeding the eye from behind, rather than inside. The human eye has a hole where the veins feed through the back then spread out across the retina. This creates the blind spot. Cephs don't have that.

That said, all eyes are "functional" to their specific purpose. The human eye is very generalized, able to see in a wide range of conditions. Other eyes in other creatures are equally specialized to their environment. None is "better". Just specialized to their purpose.
...human eye has a hole where the veins feed through the back then spread out across the retina. This creates the blind spot...

The blind spot in the human eye is not caused by veins passing through the retina... it's the visual nerve which passes through the retina and causes the black spot...

The cephalopod retina is different and doesn't have such an blind area, that's right....

FYI, at the cost of a blind spot and "backwards" wiring, the human eye gains the feature a truly spherical retina, which allows the lens to focus accurately across the entire image.
Moreover, the mammalian lens is flexible. Cephalopods have a rigid lens that has developed a clever compromise; it changes optical characteristics (diffraction angle) near the edges, to help with focusing. And the animal grows rapidly, keeping all of this properly aligned. But the lens must move forward and back to focus.

In general, cephalopods are much more sensitive to low light, as well as being able to see three of the six kinds of polarized light. (So far as I know, only the mantis shrimp sees all six.) On low light vision, I have seen references that described a cat as ten times the human sensitivity (ability to see in the dark) and at least one species of octopus as 200 times. This was not a deep sea species.

Most octopuses and squid seem to be colorblind, but we have discovered at least one species of octopus and a few squid which are not.
Interesting, I have a set of contacts based on a similar concept that allows for a minimal (sadly now not enough but for 10 years or so worked) correction for distance and close focus.
It has been parked while I handle other concerns, unfortunately. Big deadline coming Friday; after that, we'll see.

Worth noting -- in mammals, the eyes form as extensions of the brain. In cephalopods, they form as extensions (inward) of skin tissue.

And the optic gland is wired to the eye in both octopuses and squid -- and gets signals from day length that control the animal's maturity and lifespan.

Another trivia bit: Humans have rods and cones -- and we recently (2006) discovered a third type of sensor cell, that works a bit like the octopus's optic gland: These retinal ganglion cells send the brain signals on the length of the day. Each eye has about 2,000 of them, and they bypass the retina's circuits and go right to the brain.
I think that tank lights might wwell be a trigger, through accidentally improper timing. You and I have talked about this before with regard to your own octopuses.

I wonder what serves the purpose in the dumbo octopuses? It is my understanding that they do not ever see daylight.

Cold water octopuses tend to live longer, and the dumbos certainly have cold water.

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