In a Rare Biological Twist, Chameleons’ Optic Nerves Coil Like a Telephone Cord

Chameleons see the world in a way no other animal can, with eyes that move independently yet lock in perfect sync when they focus. A new study in Scientific Reports has uncovered the structure behind that ability: optic nerves coiled like telephone cords, giving each eye the slack to rotate nearly 360 degrees without damage.

“Chameleon eyes are like security cameras, moving in all directions,” said Juan Daza, an author of the study, in a press release. “They move their eyes independently while scanning their environment to find prey. And the moment they find their prey, their eyes coordinate and go in one direction so they can calculate where to shoot their tongues.”

Read More: 4 Hidden Ways Animals Camouflage Themselves

CT Scans Reveal Hidden Chameleon Anatomy

The breakthrough came in 2017, when Edward Stanley, director of the Florida Museum of Natural History’s imaging lab, noticed something unusual in a CT (Computed Tomography) scan of a tiny leaf chameleon (Brookesia minima): its optic nerves were coiled, not straight.

“I was surprised by the structure itself, but I was more surprised that nobody else had noticed it,” Daza said in the press release. “Chameleons are well studied, and people have been doing anatomical studies of them for a long time.”

Traditional dissections had damaged or displaced the delicate nerves, hiding their true shape. Only with modern CT scans could scientists visualize them intact.

“Throughout history, people have looked at chameleon eyes because they’re interesting,” said Edward Stanley, a co-author of the study. “But if you physically dissect the animal, you lose information that can tell the full story.”

Chameleons’ vision is critical to their slow, deliberate hunting style. They have prehensile tails, grasping feet, and tongues that strike prey at more than twice their body length. Their short, rigid necks restrict head movement, so their eyes do most of the work.

Read More: The Eye-Popping Truth About These 4 Animals’ Enormous Peepers

Coiled Optic Nerves Power Eye Movement

Using contrast-enhanced microCT imaging, the team scanned more than 30 species of lizards and snakes, including three chameleons from different evolutionary lineages. The scans, part of the open-access oVert (openVertebrate) project, revealed that each chameleon had optic nerves looping several times before reaching the eyes, a design unseen in other reptiles.

The nerves were up to three times longer than the straight distance from the brain to the eye, forming coils that act like springs to prevent strain as the eyes rotate. When the team looked at embryos of the veiled chameleon (Chamaeleo calyptratus), they saw the nerves begin straight and twist into loops just before hatching.

“You can compare optic nerves with old phones,” Daza said. “The first phones just had a simple, straight cord attached to the headset, but then someone had the idea to coil the cord and give it more slack so people could walk farther while holding it. That’s what these animals are doing: They’re maximizing the range of motion of the eye by creating this coiled structure.”

Scientists Probe Chameleon Vision Further

Even after centuries of study, chameleons still hold surprises. Researchers now want to know whether other tree-dwelling lizards have evolved similar optic nerve coils.

“These giants we’ve cited — Newton, Aristotle, and others — have inspired natural historians for centuries,” Stanley said. “It’s exciting to be the ones taking the next step along the long road to understanding what on earth is going on in chameleons.”

Read More: Slingshot Tongues of Chameleons and Salamanders Could Transform Tech in Medicine and Space

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article: