When it comes to vision, there are some animals in the eye kingdom that just have the evolutionary edge.
One cool trait that some animals have is the ability to move their eyes independently, which lets them track two different things at once. Can you imagine how useful it would be if you could do this in your own life?
So, what are some animals that can move their eyes independently?
Animals that move their eyes independently include chameleons, great-tailed grackles, and some other birds, some fish species like the sand lance and pipefish, and mantis shrimp. Dragonflies may also be able to see two things at once. The ability to see independently with both eyes helps these critters track prey and watch for predators.
Let’s take a closer look at the eyes of these incredible animals and what exactly they can do.
When it comes to animals with amazing eyes, chameleons are near the top of the list. They are able to see what is going on above them, behind them, and on either side of them all at once because of incredible 360-degree vision. Plus, they are one of the few animals that can move their eyes independently of one another.
Chameleons have such a wide field of vision because of their thinner body and the way their eyes bulge out let them see everything, even behind them. They can even see with their eyes closed because of a tiny hole in their eyelid.
Chameleons use their ability to see and their ability to camouflage themselves with their environment to hunt prey weight up to 30% of their own body weight. Their vision also helps them stay aware of birds, snakes, and other predators.
Chameleons also can see up to 5-10m away, making them one of the animals with the best long-distance vision, too. They use their eyes independently from one another and then shift to binocular vision when they’re ready to focus on something.
Great-Tailed Grackles and Other Bird Species
Great-tailed grackles are part of the blackbird family. While some animals have poor vision, birds like the grackle generally have good vision because they rely on their ability to see well from long distances to spot crops, insects, and all the other foods that make up their diet.
It’s also known that these birds are able to track two different targets using both of their eyes independently, which helps them find the foods that make up their diet.
Common grackles are prey for a lot of other birds and small animals, so this helps them spot predators, too.
While there hasn’t been a ton of research on the estimated 18,000 different bird species in the world and their ability to move their eyes independently, it can be inferred if grackles can do it then there are other bird species that have this ability, too.
It is known that not all bird species can do this, though. Some birds have eyes that move in different directions, but one eye moves as a counter-movement to the other. This means it actually isn’t working independently even though the bird’s eyes are pointed in different directions.
Some Species of Fish
There hasn’t been a lot of research on the many fish species and their eye movements, but one study compared the eye movements of pipefish, sand lance, and butterflyfish.
Researchers found that pipefish and sand lance can move their eyes independently, while butterflyfish move their eyes together.
The same study also found that sand lance needed visual input from both eyes to see visual stimuli clearly, while pipefish could use either eye. Butterflyfish also only needed one eye for clear vision.
Because fish have eyes on either side of their head (depending on their specific anatomy), fish that are capable of moving their eyes independently have a better field of vision. They only have blind spots directly in front of them and directly behind them.
Mantis shrimp have an incredible 16 color receptors in their eyes, whereas humans only have three. While researchers don’t think they can distinguish between colors as well as humans, mantis shrimp do excel when it comes to motility of their eyes.
The eyes of the mantis shrimp are constantly moving. They move up and down, side-to-side, and roll around in their eye stalks– and mantis shrimp seem to do this constantly and without causing any problems with vision.
Even though many species are capable of this type of eye movement, they don’t usually move their eyes as rapidly, possibly because their vision would be too blurry. It could be inferred, therefore, that mantis shrimp can also quickly process information from their surroundings.
While I’m going to add dragonflies here because they may be able to see more than one image at once, it hasn’t really been proven yet. What is known about dragonfly vision is that they have the largest eyes relative to their body size in the insect world.
While some animals have trouble seeing up, dragonflies can see 360 degrees around them all at once. With a field of vision like this, it’s no surprise that scientists have had a hard time figuring out exactly what they are seeing.
Plus, dragonflies process images at a rate of 200 frames per second (humans only process at 30-60 frames per second). This makes it hard to know if they have double vision or are just processing images from their surroundings really fast.
What Is It Called When You Can Move Each Eye Independently?
The ability to move one eye separately from the other one is called disconjugate movement (or disconjugate gaze). It’s also referred to as asynchronous optokinetic movement. By contrast, eye motions where both eyes move together are called conjugate eye movements.
While some humans have this condition from medical problems like brain stem damage, it’s also possible to train your eyes to move independently from one another. It’s estimated 5-8% of the population can move their eyes independently.
For you to be able to focus on two separate objects, however, the separate hemispheres of your brain would also have to learn to focus on those things separately. The left hemisphere would interpret information from the right eye and the right hemisphere would interpret information from the left eye.
Why Do Animals That Can Move Their Eyes Independently Have That Ability?
It can be assumed like with most things that evolve in a species over time, this ability helps a species survive. Many of the critters on this list rely on their ability to track two things at once to spot predators and prey.
The exception of course seems to be the mantis shrimp, which seems to move its eyes without needing any reason at all.
When Did Humans and Animals Develop the Ability to Move Their Eyes Independently From Their Heads?
According to researchers at Penn State University, vertebrates may not always have been able to move their eyes and heads separately. Before the earliest vertebrates emerged on land 350 million years ago, it’s believed that to see something, the animal would have to move its head to move its eyes and focus on something.
While we cannot necessarily say that evolution of this trait happened for any specific reason, it can be said that having the ability to move your eyes separately from your head conserves energy. After all, think about how much less energy is required to move your eye muscles than is needed to move your head.
Chameleons, great-tailed grackles, some fish species, and mantis shrimp are all animals that can move their eyes independently. Dragonflies may also be able to use their eyes independently, though more research needs to be done because of the fast rate that they process images from the world around them.
This all makes for some impressive eyes but it might not be as impressive as having many eyes like some other species.
Understanding the way that animal eyes work is often helpful to the field of optometry and helps scientists understand more about the human eye as well. Hopefully, you’ve enjoyed reading about these animals with the incredible ability to use their eyes independently.