The chameleon’s eyes hide a secret

Cthe bulging eyes of heleons do strange things; they pivot in different directions like periscopes as they scan their surroundings. One eye may be focused on you, while the other eye is focused on a fleeing insect.

Although scientists have been fascinated by this ability for centuries, the physiological mechanism that makes it possible remains mysterious. Until now.

A team of researchers has discovered that chameleons have two coiled optic nerves that work independently to direct the reptile’s attention to two distinct scenes. They report their findings in a Scientific reports article published today.

“Chameleons’ eyes are like security cameras, moving in all directions,” biologist Juan Daza of Sam Houston State University, lead author of the paper, said in a statement. “They move their eyes independently while scanning their surroundings for prey. And as soon as they find their prey, their eyes coordinate and go in one direction so they can calculate where to stick their tongue out.”

Read more: »See through animal eyes»

In the new study, Daza and his colleagues examined the optic nerves of three chameleon species that differ in size, evolutionary history and behavior. The brown leaf chameleon, Brookesia superciliarisis about the length of a golf tee and lives on the ground or in shrubby vegetation. The bearded pygmy chameleon, Rieppeleon brevicaudatusis somewhat larger, about the size of a pencil, and similar in its habitat use. The veiled chameleon, Chamaeleo calyptratusis the largest of the group, measuring nearly a foot long and considered entirely arboreal. By comparing disparate species, the researchers hoped to determine which features of the optic nerve structure were common to chameleons.

The high-resolution CT scan corroborated an earlier observation that a chameleon controls each of its eyes independently, but can coordinate eye movements when it locks on a target. Daza and his team discovered that this was possible through the use of optic nerves coiled like old-fashioned telephone cords. Coiling appeared in all three species. This coiling gave each species a much longer length of optic nerve than would typically be present, allowing wild movements of their eyes with much slack in their nerve tissue.

When a chameleon’s eye swivels to look at something, the coiled optic nerve unfurls to give it the length it needs. Without coiling, the study authors hypothesize that the nerve would likely be under strain from these drastic eye wanders. Looking at scans of chameleon embryos, the study authors noted that the optic nerves are initially straight during development, as in other reptiles, in the egg, but become elongated and coiled as they hatch.

This discovery distinguishes chameleons from other animals, which use different adaptations to pivot their gaze without straining the optic nerve. For example, owls rotate their necks dramatically while keeping their eyeballs steady. In rats, the optic nerves are extendable, giving them a little more flexibility to look around.

It seems that chameleons have evolved a unique approach in the animal kingdom, making this surprising creature even more of an evolutionary marvel.

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Main image: LuckyStep / Shutterstock

• Devin Reese

  Published on November 10, 2025

  Devin Reese is the editor-in-chief of Natural history and a science writer based in Alexandria, Virginia.