Coiled optic nerves of chameleons observed for the first time using CT imaging

US scientists have viewed the intricate optic nerve coil that helps chameleons to see close to 360-degrees without moving their necks using computed tomography (CT) imaging.

Writing in Scientific Reports, researchers describe how chameleons have evolved a longer, more coiled optic nerve than other lizards in order to provide ‘slack’ and reduce tension on the optic nerve as the eye rotates.

Sam Houston State University associate professor and study co-author, Juan Daza, highlighted that chameleons can move their eyes independently to scan their environment in order to find prey.

"Chameleon eyes are like security cameras, moving in all directions," he said.

“The moment they find their prey, their eyes coordinate and go in one direction so they can calculate where to shoot their tongues,” Daza explained.

The research was initiated after Florida Museum of Natural History director, Edward Stanley, noticed the tightly coiled optic nerve shape on the CT scan of a minute leaf chameleon while visiting Daza’s lab in 2017.

Both Daza and Stanley initially assumed that the structure would have been previously reported – but later discovered that this was not the case.

“I was surprised by the structure itself, but I was more surprised that nobody else had noticed it,” Daza said.

Stanley highlighted that CT imaging has advantages over traditional methods for observing the anatomy of chameleons that relied on dissection – with the corresponding risk of damaging or shifting optic nerves.

“Throughout history people have looked at chameleon eyes because they're interesting,” Stanley said.

“But if you physically dissect the animal, you lose information that can tell the full story,” he added.