A new Scientific Reports study reveals that chameleons have coiled optic nerves that allow each eye to swivel independently and then coordinate for targeting prey. High-resolution CT scans of three species — Brookesia superciliaris, Rieppeleon brevicaudatus, and Chamaeleo calyptratus — show telephone-cord-like coils that provide extra nerve length. Embryo scans indicate the nerves are straight in the egg and coil by hatching. This coiling likely prevents strain during extreme eye movements and represents a unique vertebrate adaptation.
Chameleons' Secret Wiring: Coiled Optic Nerves Explain Their Periscopic Eyes
A new Scientific Reports study reveals that chameleons have coiled optic nerves that allow each eye to swivel independently and then coordinate for targeting prey. High-resolution CT scans of three species — Brookesia superciliaris, Rieppeleon brevicaudatus, and Chamaeleo calyptratus — show telephone-cord-like coils that provide extra nerve length. Embryo scans indicate the nerves are straight in the egg and coil by hatching. This coiling likely prevents strain during extreme eye movements and represents a unique vertebrate adaptation.
02:40 PM, 11/11/2025Science
Chameleons' eyes hide a clever anatomical trick
Chameleons' prominent, bulging eyes can swivel independently, working like periscopes as they scan their surroundings. New high-resolution CT scans reveal the anatomical secret that makes those extreme eye movements possible: coiled optic nerves that provide extra length and slack, allowing each eye to move freely and then lock together when the animal targets prey.
"Chameleon eyes are like security cameras, moving in all directions," said biologist Juan Daza of Sam Houston State University, lead author of the new study. "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."
What the researchers did
Daza and colleagues used high-resolution CT scanning to examine the optic nerves of three chameleon species that vary in size, habitat and evolutionary history: Brookesia superciliaris (the tiny brown leaf chameleon, about the length of a golf tee), Rieppeleon brevicaudatus (the bearded pygmy chameleon, roughly crayon-sized), and the larger, largely arboreal Chamaeleo calyptratus (the veiled chameleon, which can approach a foot in length).
What they found
All three species showed optic nerves coiled like old-fashioned telephone cords. The coiling provides substantially more nerve length than a straight nerve would, giving the nervous tissue the slack needed for wide, rapid eye swings without putting damaging tension on the nerve.
Developmental scans revealed that the optic nerves are straight during embryonic stages inside the egg — similar to other reptiles — and then lengthen and coil before or by hatching. This indicates the coils form during late development and are a species-wide adaptation rather than an individual anatomical quirk.
Why it matters
The coiled-nerve arrangement explains how chameleons can perform independent monocular scans of their surroundings and then rapidly coordinate both eyes to aim and judge distance for their tongue strike. Other animals avoid optic-nerve strain using different strategies: owls rotate their necks while keeping the eyes relatively fixed, and rodents rely on more elastic optic nerves. The chameleons' coiled-nerves strategy appears to be a novel vertebrate solution to extreme eye mobility.
This finding, reported in Scientific Reports, resolves a long-standing physiological mystery and highlights another remarkable evolutionary innovation in chameleons.
Originally reported by Nautilus; study led by Juan Daza, Sam Houston State University.