More than meets the eye: How different animals see the world

February 10th, 2026

Written by: Catrina Hacker

When we interact with animals it’s easy to assume that they see the world the same way we do, but to what extent is that true? Just because an animal has eyes doesn’t mean they work the same way ours do. In fact, scientists think that eyes have evolved dozens of separate times throughout evolutionary history1, leading to a dizzying array of eye designs across the animal kingdom, each giving a different view of the world. For example, dogs might be man’s best friend, but they don’t see like us. Here we’ll explore just a few of the amazing eyes that can be found across the animal kingdom as we consider what it might be like to see the world through another animal’s eyes.

Sea urchin: The animal that functions like one giant eye

Our first animal eye doesn’t look like what likely comes to mind when you think of an eye. What makes an eye different from other organs and body parts is that it can sense light using sensors called photoreceptors. In humans, the light information from photoreceptors in the eye gets passed into the brain to build our visual perception of the world. Whereas our eyes are confined to two relatively small structures in our heads, sea urchins have photoreceptors all over their bodies2. This makes the whole animal function like one big eye.

Sea urchins have two types of extensions spread across the body: prickly spikes, called spines, and smaller, flexible extensions, called tube feet (Figure 1). Photoreceptors reside in sea urchins’ tube feet where they detect light2 and then pass that information on to the nerve network to guide a behavioral response. This gives sea urchins a constant 360° view of the world so that predators can never take them by surprise. While sea urchins can see more of the environment than us at any moment, their vision is pretty blurry and they don’t see color very well3. Nevertheless, these giant eyes are a remarkable example of how diverse animal eyes can be.

Figure 1. Left: The purple sea urchin Strongylocentrotus purpuratus whose photoreceptors all over its body allow it to function like one big eye. Right: A close-up picture of a sea urchin that showcases its rigid spines and flexible tube feet extending beyond the spines.

Goat: Wider pupils and wider vision

One key feature of more traditional animal eyes is the pupil, a hole that changes size to influence when and how much light enters the eye. For example, you may have noticed that your pupils become smaller when you step out into the light and larger when you’re in a dark room. This is because they are allowing more or less light to enter the eye depending on your environment.

While humans have circular pupils, goats have stunning rectangular pupils (Figure 2). Their rectangular shape comes with at least two major advantages4: first, it increases peripheral vision, allowing goats to see a much wider space around and even behind them. This helps to detect predators who may be lurking in a goat’s peripheral vision. Second, rectangular pupils shield the eyes from direct overhead sunlight. This may help goats to see better when they’re out grazing in direct sunlight. Given all these advantages, perhaps it’s not surprising that other prey animals like sheep, deer, and horses also have rectangular pupils4, giving them the same advantages.

Figure 2. Profile view of a baby goat featuring its rectangular pupils.

Chameleon: Two don’t always work as one

Perhaps the most iconic pair of animal eyes belong to the chameleon. The eyes themselves are very big, but they’re mostly covered by a scaly eyelid (Figure 3). This is because one of the chameleon’s most notable characteristics is its ability to change color. Not only does the scaly lid protect the eyes, but it lets the chameleon change the color of as much of its body as possible.

Figure 3. Left: Side view of a chameleon showing how little of the eye is left uncovered. Right: Close up of a chameleon eye. Note the very small opening for the eye surrounded by colorful skin to match the rest of the chameleon’s body.

Another notable feature of chameleon eyes is that each can rotate nearly 180° horizontally and 90° vertically, giving them a nearly 360° field of vision. Importantly, the eyes don’t have to move together. Instead, they can move independently from one another to look in different directions5 (Video 1). Being able to move its eyes in every direction allows the chameleon to stay perfectly still while it looks all around itself to spot prey. Once it has identified its prey, both eyes move to the target so the chameleon can judge how far to reach out its tongue and enjoy its meal. One factor that allows chameleons to move their eyes in all directions is the fact that the eyes are raised rather than set deep in sockets like ours (Figure 3). Another factor is that the bundle of nerves exiting the back of the eye, called the optic nerve, isextra-long and coiled5. Scientists think this extra length provides the slack necessary for chameleons to make such big eye movements.

Video 1. Close up of a chameleon head as it moves each of its eyes, one at a time.

Spider: Sometimes more is more

While us humans are stuck with a mere two eyes and two legs, most spiders get eight of each. The most famous example is the jumping spider whose vision allows it to perform daring leaps. Like many other spiders, the jumping spider has two forward-facing principal eyes and three secondary eyes on either side of its head (Figure 4). One key advantage to this design is that the eyes situated around the head allow it to see more of its surroundings than just the two forward-facing eyes can alone.

But the biggest advantage of having eight eyes comes from the fact that they’re not all the same. The biggest difference is between the principal and secondary eyes. Compared to secondary eyes, principal eyes are more sensitive, provide color vision, and can be used to look around (although not in the same way as humans)6. In fact, the principal eyes of jumping spiders provide such clear vision compared to other spiders that jumping spiders can see as well as pigeons and some dogs! On the other hand, secondary eyes can have a variety of modifications that help spiders process things on the edge of their vision, like night vision or motion sensing.

Figure 4. Close up of a female jumping spider showcasing her two principal eyes and two of her secondary eyes. The spider has four more eyes (two of three of which can be glimpsed).

Colossal squid: Owner of the biggest eyes on earth

The prize for the biggest eyes on earth goes to the colossal squid at a whopping 11-12 inches across (roughly the size of a soccer ball) (Video 2). In fact, some scientists think that the colossal squid may have the largest eyes to ever have existed in the entire history of the animal kingdom (see them here)7! Why so big? The colossal squid lives thousands of meters deep in the ocean where it needs to hunt for its meals and watch for predators in the dark waters. Bigger eyes mean more photoreceptors to capture the light, helping the colossal squid to see in the dark.

But that’s not all! Colossal squids have a special structure in each eye called a light organ that produces light through bacterial bioluminescence. When the squid moves its eyes to look directly in front of its arms the light from the light organs is concentrated in one spot enough for the squid to see its prey7, acting like bacterial flashlights. This, in addition to the large eye size, helps colossal squids survive in the dark depths of the ocean.

Video 2. News coverage showing a preserved colossal squid whose eye was measured to be 11 inches across.

These are just five examples of the many captivating eyes across the animal kingdom (see the cover photo for some more). The diversity of animal eyes matches the diversity of needs, with each perfectly suited to how that animal needs to move about the world. Aside from the fascinating biology behind different animal eyes, I can’t help but imagine what it would be like to see the world through another animal’s eyes. What might I see differently if I could see through eight eyes? Would I appreciate more about my surroundings if my photoreceptors were all over my body? How would I move about the world differently if I could move my eyes independently of one another? We might all be living in the same world, but we certainly aren’t all seeing it the same.

References

1.         Lamb, T. D., Arendt, D. & Collin, S. P. The evolution of phototransduction and eyes. Philos. Trans. R. Soc. B Biol. Sci. 364, 2791–2793 (2009).

2.         Ullrich-Lüter, E. M., Dupont, S., Arboleda, E., Hausen, H. & Arnone, M. I. Unique system of photoreceptors in sea urchin tube feet. Proc. Natl. Acad. Sci. 108, 8367–8372 (2011).

3.         Al-Wahaibi, M. K. & Claereboudt, M. R. Extraocular vision in the sea urchin Diadema setosum. Mar. Freshw. Behav. Physiol. 50, 31–40 (2017).

4.         Banks, M. S., Sprague, W. W., Schmoll, J., Parnell, J. A. Q. & Love, G. D. Why do animal eyes have pupils of different shapes? Sci. Adv. 1, e1500391 (2015).

5.         Collins, E. et al. A new twist in the evolution of chameleons uncovers an extremely specialized optic nerve morphology. Sci. Rep. 15, 38270 (2025).

6.         Morehouse, N. Spider vision. Curr. Biol. 30, R975–R980 (2020).

7.         The eyes of the colossal squid | Te Papa. https://tepapa.govt.nz/discover-collections/read-watch-play/colossal-squid/anatomy-colossal-squid/eyes-colossal-squid.

Cover photo made by Catrina Hacker with the following images:

Figure 1 contains images by Taollan82 on Wikimedia Commons under a Creative Commons Attribution 3.0 Unported license (left) and Jerry Kirkhart on Wikimedia Commons under a Creative Commons Attribution 2.0 Generic license (right).

Figure 2 by Béria L. Rodríguez on Wikimedia Commons under a Creative Commons Attribution-Share Alike 3.0 Unported license.

Figure 3 contains images by Sharp Photography on Wikimedia Commons under a Creative Commons Attribution-Share Alike 4.0 International license (left) and Brice Miller on Wikimedia Commons under a Creative Commons Attribution-Share Alike 4.0 International license.

Figure 4 by Computer Hotline on Wikimedia Commons under a Creative Commons Attribution 2.0 Generic license.

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