Octopuses share a very peculiar feature that, despite quickly catching observers’ attention, is rarely spoken of… their eyes. Yes! They are round, prominent, and reveal their relentless curiosity. Taking our star student, the Octopus vulgaris, as a reference here, we will review this intriguing organ from the inside out to better understand how octopus’ eyes work.
The Common Octopus, Octopus vulgaris, is actually a species complex (or group of octopuses under the same name) present in all tropical, subtropical, and temperate waters worldwide. The OG Octopus vulgaris predominantly inhabits the Mediterranean Sea.
It may be called “common” but this octopus is anything but. Known to be a renowned escape artist, the Common Octopus has so many special qualities, but today we are going to be focusing on its eyes!
Let’s take a closer look…
Outside The Eye Of The Common Octopus
Did you know the Octopus vulgaris’ eyes are of remarkable size, reaching up to 2 cm at its full development at adult age?
While this might not strike you as gigantic, it is disproportionately large compared to the rest of its body.
The octopus often raises its eyes, as it can both bulge and retract them. They are positioned laterally (to the side or away from the middle of the head) and can move independently.
🐙 Octopus Fun Fact
One of the most fascinating elements about this sea creature is that it is a mollusk with vertebrate-like eyes!
The Anatomy Of An Octopus Eye
When it comes to the actual structure of an octopus’s eye, there are actually a few layers to it:
- Cornea – Protects the surface of the eye
- Lens – Adapt to visual sharpness
- Pupil – Retracts and dilates
- Colored Iris – Surrounds the pupil
- Retina – Located at the back of the eye and made up of neurons sensitive to light
Indeed, the octopus has a muscular ring-shaped skin folded around its eye that can close and open similarly to an eyelid. Therefore, don’t be too surprised if you ever see an Octopus vulgaris winking at you!
Eye Color And Shape
No jealousy is felt among Octopus vulgaris; they are all capable of switching eye color and they do not need a colored lens! Their eyes contain a cellular layer of chromatophores (the cells responsible for color change in octopus’s skin) that allow them to match their eye color to their outfits.
The chromatophores, present both in their iris and in their skin, provide a complete camouflage of the octopus body!
One of the most important features of the octopus eye is its pupil. Elongated and horizontal, it reminds us of goats’. It can tighten into a thin slit, making the eye almost invisible.
The octopus’s pupil is also sensitive to light! Like us, the less light there is, the more it expands to be able to absorb the maximum amount of light.
🐙 Octopus Fun Fact
For an octopus, pupil dilation is variable and can be controlled.
For example, the octopus can dilate it, making it almost round, to appear more threatening. That is what’s called a deimatic signal: when an animal uses intimidation to defend itself when facing a predator!
Inside The Octopus Vulgaris Eyes
So, now that we know what the anatomy of their eyes is… What is it like inside?
Overall, we have seen that the biological organization of the octopus’ eye is close to vertebrates’. But, through the microscope, their eyes prove to have the same photoreceptors (special cells that help detect light) as insects. They are called rhabdoms and differ from ours, so-called ciliate photoreceptors.
These two types of photoreceptor cells have distinct biological forms but are both means of optimizing light income- they increase the surface of contact with the light either by developing:
- Microvilli (rhabdoms)
- Cilia (ciliates)
Vertebrates have ciliary photoreceptors more commonly known as rods and cones that are sensitive to dim and bright light.
Cones also contain visual pigments (up to three in mammals; red, blue, green) that allows color vision. The Common Octopus has a different type of photoreceptor (rhabdomeric type) that is also found in arthropods (insects) and other mollusks.
No Blind Spot (Must Be Nice!)
There is another difference between octopus eyes and human eyes: the retina of their eye does not have the same innervation (distribution of nerves) as ours and that has major implications.
But first, let’s remember that retina cells are responsible for capturing light and they are distributed by cells that must transmit the information to the brain.
Well, in octopuses, the retina is innervated from below, which allows the nerve endings not to cover the inside of the retina; while in vertebrates, these nerves are above the retinal cells and end up obstructing part of the retina forming the optic nerve.
There is no transmission of information in this spot since there are no retinal photoreceptors. This is the blind spot!
Fun Blind Spot Test: Do This At Home!
To figure out your blind spot, look at these two little octopuses and do this experiment.
- Cover your right eye and look at the right octopus with your left eye.
- Look forward or backward from the screen until you notice the left octopus disappear (you can replicate the experiment by covering the left eye and looking at the left octopus).
And now, you have just highlighted your blind spot! Your eye is not able to take this information into account.
The octopus will always see both figures because the anatomy of its eye does not have a blind spot.
Looking Through The Eyes Of The Octopus
The octopus has mainly monocular vision (looking through one single eye) and each eye is independent. This increases the overall visual field, but it undoubtedly decreases the perception of depth in comparison with our binocular vision (looking through both eyes).
🐙 Octopus Fun Fact
In addition, it has been shown in the Octopus vulgaris that one eye tends to be preferred over the other! Just as we can be left-handed or right-handed, there are some Common Octopuses who naturally prefer to observe with their left eye over their right eye and vice versa.
How good is an octopus’s eyesight?
Studies suggest the octopus is rather short-sighted in a resting state; its eyes are well suited for seeing nearby objects.
Even so, octopuses have excellent vision with keen sharpness comparable to fish and other vertebrates.
🐙 Octopus Fun Fact
We don’t focus the same way. The Common Octopus has a stiff lens of fixed focal length, which is normally focused on fairly close objects. The focusing process is achieved by changing the distance between the lens and the retina, like a camera lens!
In vertebrates, such as us, the distance between the lens and the retina is fixed: we focus by changing the shape of the actual lens.
In what colors does the octopus see?
The octopus has only one visual pigment. It is monochromatic and therefore does not see colors. It only differentiates light and dark (or brightness), in a range of grays.
I can already picture you being disappointed by those sad shades of grey. But, don’t you worry, the octopus has more than one trick up its sleeve to surprise you!
How does he manage to be the king of camouflage without seeing any colors?
Of course, there is a well-kept secret…
Scientific research is still trying to unravel it. Octopuses may see colors but not by the same means as we do! One research hypothesis lies in the shape of the pupil and the use of chromatic aberration.
Chromatic aberration is an optical aberration (like a lens) that produces a blurry image with iridescent edges. Our eyes are adapted to avoid this chromatic aberration, but an octopus eye would be adapted to improve it.
This aberration would be linked to the particular shape of the cephalopod pupils, which act as a prism decomposing white light. Some U or W-shaped pupils (like Cuttlefish) would further promote this phenomenon.
It would be a whole different way of dealing with colors!
Take A Look Through The Octopus Vulgaris Eyes!
Now you know what it’s like to explore and see as a Common Octopus would. What did you think? Let us know in the comments done below!
If you want to educate yourself some more about all sorts of different cephalopods, take a look at our encyclopedia. Or, what we call it, our Octopedia!
Connect with other octopus lovers via the OctoNation Facebook group, OctopusFanClub.com! Make sure to follow us on Facebook and Instagram to keep up to date with the conservation, education, and ongoing research of cephalopods.
More Posts To Read:
- Meet the Cockeyed Squid: the Deep-Sea Animal with a Giant Eye!
- 10 Facts About Baby Nautilus!
- Does Octlantis Exist?
- Dumbfounding Flapjack Octopus Facts You NEED To Know!
- What Is The World’s Biggest Octopus?
Fanny is a young scientific mediator with a background in animal and cellular biology. She is very passionate about science and underwater life! Her goal is to make science readily accessible to everyone because, according to her, when you understand your environment, you are more likely to love it and therefore protect it.
Bulgarian born in Tunisia, she still lives on the Mediterranean coast, but on the other side of the sea, in the city of Marseille in France.