A chameleon’s eyes are one of its defining features. Everybody has seen how they bulge out the side of a chameleon’s head and appear to swivel about in all directions, but fewer people know precisely how their eyes work and what makes them so unique.
Here are 8 amazing facts about a chameleon’s eyes that will help you appreciate just how wonderful and unique these creatures are.
1. Chameleons only have one eyelid
Most animals with eyelids have two of them, an upper and a lower that blink to clean and moisten the eyeball. Chameleons, on the other hand, don’t blink because they have one cone-shaped eyelid that fuses to their eyeball and covers the entire eyeball only leaving a tiny opening slit exposing the pupil.
There is a small membrane called the nictitating membrane that acts similar to an eyelid. This is on the side of the eye closest to the chameleon’s nose and this moves across the pupil to aid cleaning of the eyeball.
2. Chameleons have a negative lens and a positive cornea
A negative lens means it is a concave lens and this allows for a large retinal image leading to greater focusing and magnification. Chameleons have the highest level of magnification amongst all the vertebrates. To accompany the negative lens, chameleons have positive corneas meaning it is convex. This improves further the level of magnification and improved sight resolution. A chameleon can effectively see in high definition.
3. Chameleons have panoramic vision
This is thanks to the unique anatomy of their eyes. A chameleon’s eyes bulge out the side of their head. What enables this is not only the muscular eyelid that stops the eyeball popping out but also a very deep socket, much like our own, that holds the eye in place.
To enable the panoramic vision of 180 degrees horizontally and 90 degrees vertically, chameleons eyes are mounted on small turrets that move independently so one eye can see in front and the other behind, meaning a chameleon can constantly scan their environment for prey and predators. Their total field of vision is 342 degrees with a blind spot of 18 degrees directly behind their head.
4. Chameleons have monocular and binocular vision
The negative lens and positive cornea in a chameleon’s eye mean it is capable of corneal accommodation for depth perception. Most other vertebrates use lens accommodation for this purpose. This gives a higher resolution of focus. Scientists used to believe chameleons used stereopsis, the combining of images taken from each eye, to focus on their prey. Now there is evidence that chameleons perceive depth by taking information from just one eye, hence the monocular vision.
Accommodation is uncoupled in both eyes while a chameleon scans the environment. The best way to describe this is like having two movies playing in your head that you can watch each one separately or both at the same time. However, when one eye focuses on an insect it couple to the other eye guiding corneal accommodation in it and both eyes effectively become a pair of binoculars that zoom in on their target. This coupling and uncoupling occur in less than the blink of your own eye.
Not only is this type of vision system extremely effective at scanning for and hunting prey, it is also equally effective for escaping predators. If a chameleon spots a potential predator it is able to uncouple its eyes, focus monocularly with one eye on the danger and use the other eye to scan the environment for an escape route.
5. Chameleons can see in the ultraviolet spectrum
Scientists recently discovered that certain parts of a chameleon’s bone structure glow when placed under UV light. This occurs in nearly all species tested. The process is called biofluorescence, meaning chameleons absorb light and then reemit it in a different color. As chameleons can see in the ultraviolet spectrum, it’s though this biofluoresence is another way for chameleons to communicate with each other. This is more common in sea life and very rare in land species, making the chameleon yet more fascinating and unique.
6. Chameleons are virtually blind in the dark
The photoreceptors that enable the retina to comprehend an image are divided into rods and cones. Chameleons have mainly cones and hardly any rods. This means they see the world mainly in colors with very little contrast making them virtually blind in the dark.
7. Chameleons can see for miles
OK not miles but they can see things in very sharp detail up to half a mile away! This is absolutely astonishing when you consider that you can see nowhere near that distance in any detail and you are much larger than a chameleon with a much larger brain to process images. This is down to the small opening a chameleon’s eyelid allows over its pupil, in effect making it a tiny camera with pinpoint sharpness of detail.
8. Chameleons have self cleaning eyes
When something irritating gets in our eyes the temptation is to rub our eyes with our hands to relieve the irritation, we also use eye drops and wash our eyes with water to remove the irritant. Chameleons, however, have a much more efficient method. Whenever their eyes get irritated they push their eyeballs right up against the eyelid. The nictitating membrane mentioned earlier then moves across the eyeball in a wiping motion to clean the eyeball and remove the irritant.
Chameleons also bulge their eyes right out at times of distress. My chameleon would sometimes turn black and glare with big bulging eyes at anyone new who entered the room his cage was in! Chameleons can also retract the eyes in at times of stress too.
So, as you can see chameleons have a really fascinating vision system completely unique amongst vertebrates and almost unique amongst all animals. For more general facts about chameleons check out my 50 nifty chameleon facts article.
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