How Many Eyes Does An Octopus Have?

How Many Eyes Does an Octopus Have?

Octopuses have two large eyes and very superior vision. When it’s dark, the pupil of the octopus eye is circular, while in bright light, it compresses to a horizontal slit.

How Big are Octopus Eyes?

Compared to their body, the octopus typically has very large eyes. For example, the Common Octopus measures in the 12-to-36-inch range and weighs from 6.6 to 22 pounds. Their eye diameter ranges between half an inch to one inch.

In contrast, the adult human eye also measures about one inch, yet we are considerably larger than the average octopus.

Octopus Eyes vs Human Eyes

Even though the human and octopus eyes are structurally similar, there are also key differences affecting how octopuses see compared to how we do.

One main difference is the way the octopus eye vs. the human eye focuses. Octopuses focus by moving the lens in or out, similar to the way that you would focus a camera or telescope. The human eye focuses by using muscles to adjust the shape of the lens. The octopus movable lens allows them to focus more quickly on objects, even those that are moving, and they likely have fewer vision problems than people.

Human and octopus eyes have many same eye structures, including the lens, iris, retina, optic nerve, pigment cells, and photoreceptors. However, due to the moveable lens, octopuses don’t have corneas.

How Do Octopus Eyes Develop?

The human eye, and those of other vertebrates, develop as outgrowths of the brain, the octopus eye forms as an invagination while still in the egg. The eye forms from an inward fold in an outer layer. This means the optic nerve connects to the retina without having to pass through the photoreceptive layer at the back of the eye.

Can Octopus Eyes See Color?

The human eye has three kinds of photoreceptors, each singularly sensitive to red, blue, or green light, but the octopus eye contains only one type of light receptor.

This technically means they only see black and white, are colorblind, and shouldn’t be able to distinguish different colors. So how is it possible that octopuses can change color rapidly to blend into their surroundings?

How do Octopuses See Color?

Originally it was believed that octopuses were colorblind, but more recent studies indicate that they can differentiate between colors.

The answer may lie in the ability of their unique U-shaped, W-shaped, and dumbbell-shaped pupils to act as prisms and force light to enter the eye in all directions at once. In contrast, the human pupil is round and allows light to enter only from a single direction.

Using an effect called chromatic aberration, the octopus can change the depth of the eyeball or alter the distance between the lens and the retina to process the different light wavelengths, allowing for colors to be detected.

It would explain why octopuses appear to be able to see different colors and why they change their skin color for camouflage or to warn away other animals.

Do Octopus Eyes Have a Blind Spot?

You may not know it, but humans have natural blind spots in both eyes. Your retina is made up of tiny, light-detecting cells called photoreceptors. Where the optic nerve connects to the retina has no light-sensitive cells and creates a blind spot. You don’t notice because your other eye compensates for it.

But the octopus doesn’t have blind spots. Their optic nerve extends from the back of the retina instead of the front so that no part of the retina is blocked.

Are Octopuses Nearsighted?

Octopuses are myopic or nearsighted, which means they can see nearby objects. However, they’re able to contract a muscle around their eyes which moves the lens closer to the retina and allows them to have near normal-sightedness.

Can Octopuses See Polarized Light?

Polarized light is light that vibrates in only one direction. The human eye is not particularly sensitive to polarized light. The closest we get to distinguish it is when wearing polarized sunglasses to cut down on glare to protect our eyes.

On the other hand, cephalopods, like octopus, are sensitive to polarized light. The ability to see polarized light can help with various tasks, including navigation, habitat localization, contrast enhancement, and communication. Polarized vision also allows the octopus to differentiate objects, similar to how we have color vision.

Do Octopuses Have Night Vision?

Most octopus species are nocturnal, meaning they’re active at night. Luckily, they can see very well both at night and during the day. They typically hunt at night and may even venture on land in search of food.

Do Octopus Eyes Work Together or Independently?

Because their eyes are on the sides of the head, the octopus primarily uses monocular vision and can move its eyes independently. Each pupil is controlled by its own muscles and nerves and gives octopuses the ability to rotate their eyes up to 80 degrees in either direction.

Do Octopuses Have Blue Eyes?

Although octopuses do not have blue eyes, they do have blue blood. Octopuses have a high metabolic rate that requires a lot of oxygen. The color comes from copper-based hemocyanin a protein that transports oxygen throughout their bodies more efficiently at low temperatures and low oxygen concentrations.

Can Octopuses Detect Light Without Using Their Eyes?

Octopuses have thousands of cells called chromatophores just beneath their skin surface. These chromatophores contain opsin molecules which are light-sensitive proteins also found in their eyes to help them detect light. Theoretically, this means octopuses can sense light with their skin.

Do Octopuses Smell with Their Eyes?

You may have noticed that the octopus doesn’t have a nose, but that doesn’t mean they can’t detect smells. In fact, they have an excellent sense of smell. Octopus can smell due to chemical sensors at the ends of their arms that not only feel but smell and taste as well. It’s why they often stick one arm into an opening. Octopuses are able to detect predators at a distance and get out of the way.

References

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