How Do Chameleon Eyes Work? Looking Two Ways at Once

What makes chameleon eyes unusual?

Most of the eyeball is hidden. A chameleon’s upper and lower eyelids are fused into a single scaly cone, called a turret, with only a small opening in the center for the pupil. The turret moves together with the eyeball, so the pinhole always points where the eye is looking.

The eyes also bulge far out from the sides of the head. That position, plus the turret design, allows each eye to swing through a very wide arc, horizontally and vertically. In the veiled chameleon, the panther chameleon and other species, you can watch one eye roll forward while the other rolls up and back, a sight that makes chameleons look almost mechanical.

Can chameleons really look in two directions at once?

Yes. Unlike human eyes, which always move together, a chameleon’s eyes are not locked to each other. While searching, each eye makes its own quick, jumping movements, called saccades, and points in a different direction. Together they can survey nearly the whole sphere around the body, a field of view that is often described as close to 360 degrees, without the chameleon turning its head.

This is a big advantage for an animal that hunts by sitting still. A chameleon can keep watch for insects in front, for birds overhead and for snakes behind, all without moving and giving away its position.

What happens when a chameleon spots prey?

The behavior changes completely. Once one eye has found a possible meal, the chameleon turns its head toward it and swings the second eye forward too. Now both eyes look at the same target, and their movements become coordinated.

A 2001 study by the biologist Matthias Ott showed that while chameleons track prey with both eyes, the quick jumping movements of the two eyes become synchronized, even though the eyes still move independently during searching. The animal then aligns its head and body, judges the distance and fires its ballistic tongue, which is covered in our article on how fast a chameleon’s tongue is.

How do chameleons judge distance?

Humans judge distance mainly by comparing the slightly different images from our two eyes, known as stereo vision. Chameleons seem to rely mostly on something else: focus.

In a classic 1977 experiment, Lindsay Harkness covered one eye of chameleons and found that they could still judge distance and strike prey accurately. Then she placed lenses in front of the eye: a lens that changed the focus made the chameleons misjudge the distance in a predictable way. This showed that the chameleon judges how far away its prey is from how much it has to adjust its focus, a process called accommodation.

The chameleon’s eye is especially good at this. In 1995, Ott and Frank Schaeffel discovered that the chameleon lens has negative power, unlike the focusing lens of almost all other vertebrates. Combined with a strongly curved cornea, it works like a telephoto lens, projecting a large, magnified image onto the retina. This makes focus very sensitive to distance and gives chameleons a very large retinal image for an eye of their size.

How sharp is chameleon eyesight?

Chameleons are visual hunters with sharp eyes. Each retina has a fovea, a small central pit packed densely with cone cells, where vision is sharpest. The magnifying lens system spreads the image over this dense patch of cells, which helps the chameleon pick out small insects among leaves and twigs several meters away.

Vision is also tuned to motion. A still insect is easy to overlook; a moving one is quickly noticed, which is one reason chameleons often strike just after prey starts to move.

Can chameleons see color and ultraviolet light?

Yes. Like many lizards, chameleons have several types of cone cells, including ones sensitive to ultraviolet light, which humans cannot see. Colored oil droplets inside the cones are thought to fine-tune color perception.

Good color vision is essential for chameleons because they talk to each other in color. Rival males flash bright patterns, and females show special colors to signal whether they will mate. Read more in why chameleons change color.

How do chameleon eyes compare with other animals?

Few animals combine independent, all-around scanning with precise forward targeting. Many prey animals, such as rabbits, have wide panoramic vision but poor depth judgment straight ahead. Many predators, such as owls, have forward-facing eyes with excellent depth perception but a limited field of view; see how owl eyes work. Jumping spiders, described in how well jumping spiders can see, also use a telephoto-like eye design to judge the distance to prey before they pounce.

The chameleon gets the best of both: a lookout’s panoramic view while waiting, and a sniper’s focused aim at the moment of the strike.