The chameleon’s eyes, which rotate in all directions and can look in two different directions at the same time, have fascinated humanity since Ancient Greece
Aristotle, more than two thousand years ago, even said that these animals didn’t have optic nerves-their eyes were directly connected to the brain.
For centuries, philosophers, doctors, and scientists tried to understand the secret behind this almost magical movement.
Only now, in 2025, has the mystery finally been solved: the optic nerves of chameleons are coiled in long spirals, like springs, allowing the eyes to rotate almost 360° without breaking or stretching.
This structure is unique among all lizards on the planet.
“The chameleon’s eyes are like security cameras that monitor everything around them,” explains Juan Daza, professor at Sam Houston State University and lead author of the study.
“Each eye moves independently as the animal searches for prey.
When it finds an insect, both eyes immediately align in the same direction to calculate the distance and precisely shoot its tongue.”
A discovery almost no one has seen
It all began in 2017, when Edward Stanley, from the Florida Museum of Natural History, was performing a CT scan of a tiny leaf chameleon (Brookesia minima).
Inside the skull, he saw something never before recorded: the optic nerves coiled in perfect spirals.
The two researchers were so shocked that they thought someone must have already described it.
They searched entire libraries, texts in Latin, French, Italian, and even mixtures of ancient languages.
Nothing.
Neither Isaac Newton, who wrote about the chameleon’s eyes in 1704, nor the 19th-century anatomists who drew pieces of the nerve had noticed the complete coil.
Why hadn’t anyone seen it before? Because, for centuries, the only way to study it was by dissecting the animal with a scalpel.
Upon opening the skull, the delicate optic nerve would become displaced or severed, losing the coiled shape that the CT scan now reveals without touching the animal.
Masters of life in the trees
Chameleons live in Africa, parts of Europe, and Asia, almost always in the branches.
To do this, they have evolved incredible adaptations: a tail that coils and holds like an extra hand, feet shaped like pincers, and extremely slow movement so as not to be noticed.
They don’t have speed-nor do they need it.
Their weapon is their catapult-like tongue, which goes from 0 to 100 km/h in one hundredth of a second and can be more than twice the length of the animal’s body.
Since their necks hardly turn, the solution was to let their eyes do the work.
In other animals, optic nerves are straight or slightly wavy.
In chameleons, they’ve become like old telephone springs: the more the eye rotates, the more the spiral uncoils, providing slack without stretching or twisting the nerve.
How the spring forms
Scientists analyzed veiled chameleon (Chamaeleo calyptratus) embryos at different stages.
Early on, the optic nerves are straight.
Near birth, they grow so much that they begin to coil up on their own inside the skull.
When the hatchling emerges from the egg, it is born with both eyes fully mobile and the springs ready.
Why does only the chameleon have this?
Among vertebrates, those with large eyes generally choose one of two strategies: turning their necks a lot (like owls and lemurs) or having flexible optic nerves (like us humans).
Chameleons can hardly turn their necks, so they invented the spring-a solution so rare that it only appears in some invertebrates, like the upright-eyed fly.
“It’s like an old telephone cord,” Daza jokes.
“In the beginning it was straight and short.
Then someone coiled it to give it more reach.
The chameleon did the same thing with its optic nerve: it coiled it so the eye could rotate as much as it wanted.”
A silent revolution
The discovery was only possible thanks to two advances: tomography scans that see inside the skull without opening anything and projects like oVert, which freely provide 3D models of thousands of animals to scientists worldwide.
Analyzing more than 30 species of lizards and snakes, the researchers confirmed: only chameleons have such long and coiled optic nerves.
After Aristotle, Newton, dozens of anatomists and more than two thousand years of curiosity, the secret was there, hidden inside the chameleon’s head, waiting for the right technology to be seen.
As Edward Stanley said: “It’s exciting to be the one to take the next step on this long road of understanding what the heck goes on inside a chameleon’s head.”
Nature still holds surprises – and sometimes, the biggest ones were right in front of us the whole time.
Published in 11/18/2025 09h41
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
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