Macro of my gecko’s eye
Nocturnal geckos have to be able to block out the bright sun during the day while still retaining excellent night vision, which is why they have long zig-zagged pupils that can tightly constrict to let in only pinpoints of light. Interestingly, while humans cannot see colors in dim moonlight, these animals can discriminate between colors and their eyes are calculated to be almost 350 times stronger when it comes to seeing color.
Mesmerising!While humans tend to only think about their own vision and eyesight, eyes work in all kinds of different ways, allowing some animals to see in ways that humans can only imagine. Here are a few things you should know about a few animals with highly specialized eyes.
Like many predators, owls have their eyes located together in the front of their face, which allows them excellent depth perception during their hunting expeditions –particularly in low-light situations. Interestingly though, these massive eyes are fixed in their sockets and can barely move. This is why the owl can turn its head so far.
Gharials are ancient creatures that are practically living fossils. Despite this, they have extremely well-evolved eyes that are located in such a way that they can keep almost their entire head underwater and leave their eyes out to look out for prey. Their eyes are also primed for night vision, as a thin, mirror-like structure at the back of their eye helps reflect light that was not already absorbed by the eye back into the eye a second time. When lights are shown on the creatures at night, their eyes will reflect the light so brightly that it looks like they are glowing.
Hippos can see under the water with excellent precision, but what is really fascinating about their eyes is the clear layer of membrane that protects them from debris found underwater.
Chameleons have some of the most unique eyes in the entire animal kingdom. They do not have an upper and lower eyelid, but instead just have a cone with a small opening just big enough for their pupils. Each cone can be separately rotated and the chameleon can actually look at two separate things in completely different directions at the same time. This visual advantage makes them exceptionally adept at hunting flying insects as they quickly buzz by.
Like most insects, butterflies have compound eyes, which are made of hundreds of microscopic, six-sided lenses that allow them to see in every direction simultaneously. While this type of vision prevents the bugs from seeing things in sharp focus, butterflies can see ultraviolet light, which is invisible to the human eye. This aspect of their vision helps to lead them to flowers filled with delicious nectar.
The square pupils of goats attract a lot of attention, but they aren’t just there to look pretty. The width of the pupils allows the animals to see at a 330 degree angle, as opposed to humans who generally see at around a 185 degree angle.
Frogs are well-known for their big eyes, but few people know why their eyes bulge out. They can protrude their eyes to help them see above the surface while they are underwater. When they close their eyes, they pull them back, where they are covered by a top opaque eyelid and two eyelids made of of thin, translucent membrane.
Some of the most evolved eyes in the entire animal kingdom belong to cuttlefish. Their strange, w-shaped pupils are unable to register color, but can see the polarization of light, which allows them to see contrasts, even in dim light. While humans reshape their eye lenses to see things in better focus, the cuttlefish reshapes its whole eye. Additionally, internal sensors in the eye allow the creatures to observe things in front of them and behind them at the same time.
has evolved a unique pair of eyes that settle at the tips of their eyestalks, located on the head, and measure around 0.3mm across! This may sound tiny but with a spherical lens, the clever use of extending and withdrawing the eyes, while keeping the body stable, allows the snail to be a crafty spy and look around corners without exposing itself! Put that in your pipe James Bond! When sensing any danger the snail is able to quickly retreat its eyes into a protective shell, keeping them free from injury!
is a small (about squirrel sized) nocturnal primate, found in the rainforests of South Eastern Asia. It is the only fully predatory primate in the world, feeding on lizards and insects and is even known to catch birds in mid flight. It’s most remarkable feature; however, are its enormous eyes, the largest of any mammal, relative to body size. If your eyes were proportionally as big as those of the tarsier, they would be the size of grapefruits. These enormous eyes are fixed in the skull, and can´t be turn in their sockets. To compensate for this, the tarsier has a very flexible neck, and can rotate its head 180 degrees, just like an owl, to scan for potential prey or predators.
With each eye weighing more than its brain, the tarsier has extremely acute eyesight and superb night vision; it has even been suggested that they may be able to see ultraviolet light. On the other hand, they seem to have very poor color vision, as is the case with many nocturnal animals (including house cats and owls, for example).
Four eyed fish
Found in Mexico and Central America, as well as Northern South America, these are small fish measuring up to 32 cm and usually found in fresh or brackish water (although they have also been seen in marine coasts). They feed mostly on insects, so they spend most of their time swimming at the surface. Despite their name, four eyed fish have only two eyes. However, these eyes are divided by a band of tissue and each half of the eye has a pupil of its own. This bizarre adaptation allows the four eyed fish to see perfectly (and at the same time) both above and below the waterline, scanning for both prey and predators.
The upper half of the eyeball is adapted to vision in air, while the lower half is adapted to underwater vision. Although both halves of the eye use the same lens, the thickness and curve of the lens is different in the upper and lower eye halves, thus correcting for the different behavior of light in air and water. This means that when the four eyed fish is completely submerged, the upper halves of the eyes are out of focus. Fortunately, the fish spends almost its entire life in the surface, and it only has to dive completely once in a while to prevent the upper halves of the eyes from dehydrating.
Stalk eyed fly
These small but spectacular creatures are mostly found in the jungles of South East Asia and Africa, with a few species also found in Europe and North America. They get their name from the long projections from the sides of the head with the eyes and antennae at the end. Male flies usually have much longer stalks than females and it has been confirmed that females prefer males with long eyestalks. Males during mating season often stand face to face and measure their eyestalk’s length; the one with the greatest “eye span” is recognized as the winner.
Male stalk eyed flies also have the extraordinary ability to enlarge their eyestalks by ingesting air through their mouth and pumping it through ducts in the head to the eyestalks. They do this mostly during mating season.
The spookfish is a deep water, ghostly-looking fish that has some of the most bizarre eye structures known to science; each eye has a lateral swelling called a diverticulum, separated from the main eye by a septum. While the main part of the eye has a lens and functions in a similar way to other animal eyes, the diverticulum has a curved, composite mirror composed of many layers of what seem to be guanine crystals. This “mirror” is superior at gathering light than the normal eye; the diverticulum reflects light and focuses it onto the retina allowing the fish to see both up at down at the same time.
is the only vertebrate known to use a mirror eye structure to see, as well as the usual lens. Spookfish are found worldwide but are rare to see, since they spend most of their lives at a depth of 1000-2000 meters. They feed on small crustaceans and plankton, and measure about 18 cm in length.
The glasshead barreleye
a fish that lives 800 to 1,000 meters down, has an upward-pointing eye that helps locate predators, PhysOrg reported. This cylindrical eye has a “mirror-like second retina which can detect bioluminescent flashes created by deep-sea denizens to the sides and below,” the article explains. How does it work? “The light coming from below is focused onto a second retina by a curved mirror composed of many layers of small reflective plates made of guanine crystals, giving the fish a much bigger field of vision.” This is one of two known cases of reflector eyes in vertebrates (some mollusks and crustaceans have them), but the two cases are in different genera. “That indicates that two related but different genera took different paths to arrive at a similar solution – the reflective optics and a second retina to supplement the limited vision of the conventional refractive cylindrical eye.”
Ogre faced spider
Spiders are popularly known for having many eyes (although this varies greatly among the different species, with some having two, four, six or eight eyes). The Ogre-faced spider has six eyes, but it looks as if it only had two because the middle pair is greatly enlarged. This is an adaptation for a nocturnal lifestyle; ogre faced spiders have superb night vision not only because of their huge eyes, but because of an extremely light sensitive layer of cells covering them.
This membrane is so sensitive in fact, that it is destroyed at dawn and a new one is produced every night. Ogre faced spiders are unusual because they can see perfectly at night even though they lack tapetum lucidum, a reflective membrane that helps others spiders (and other predators such as cats) to see in low light conditions. As a matter of facts, scientists believe that ogre faced spiders have better night vision than cats, sharks, or even owls (which can see up to 100 times better than humans at night!).
And finally, we get to the animal with the weirdest and most amazing eyes in the world. The mantis shrimp is not actually a shrimp, but a different kind of crustacean from the Stomatopoda order. Known for its aggressiveness and formidable weaponry (they have an extremely sharp and powerful claw and can split a human finger in two or even break a glass aquarium with one single strike), mantis shrimp are voracious predators found mostly in tropical waters.
Their eyes are compound, like those of the dragonfly, although they have a far smaller number of ommatidia (about 10.000 per eye); however, in the mantis shrimp each ommatidia row has a particular function. For example, some of them are used to detect light, others to detect color, etc.
Mantis shrimp have much better color vision than humans (their eyes having 12 types of color receptors, whereas humans have only three), as well as ultraviolet, infrared and polarized light vision, thus having the most complex eyesight of any animal known. The eyes are located at the end of stalks, and can be moved independently from each other, rotating up to 70 degrees. Interestingly, the visual information is processed by the eyes themselves, not the brain.
Even more bizarre; each of the mantis shrimp’s eyes is divided in three sections allowing the creature to see objects with three different parts of the same eye. In other words, each eye has “trinocular vision” and complete depth perception, meaning that if a mantis shrimp lost an eye, its remaining eye would still be able to judge depth and distance as well as a human with his two eyes. Scientists are only starting to understand the mysteries of Stomatopod vision; for the moment, we can only imagine what the world really looks like to a mantis shrimp.
Trilobites were one of the most successful animal groups of all times, thriving for almost 300 million years long before dinosaurs appeared on Earth. Although some species were eyeless, most of them had compound eyes similar to those of insects. The weird thing about trilobite eyes is that their lenses were made of inorganic calcite crystal, a mineral that is also the main component of limestone and chalk. In its purest form, calcite is clear, thus being an adequate if unorthodox material for an eye lens.
These crystal eyes are unique to trilobites, with the compound eyes of modern invertebrates being made of chitin, an organic substance. Due to their unusual composition, trilobite eyes were completely rigid and could not be adjusted to focus; instead, the trilobite corrected its focus with an internal eye mechanism which not only solved any potential problems caused by the mineral lens, but also gave the trilobite such good vision, that it could keep both close and distant objects in focus at the same time.
As if that wasn´t bizarre enough, some trilobites had really weird looking eyes; a few had their eyes at the end of long projections, just like the Stalk Eyed Fly, while others had overhanging “eyeshades” on top of the eye, protecting it from bright sunlight. Being made of calcite, trilobite eyes fossilized easily, and therefore we probably know more about trilobite eyes and vision than about those of any other prehistoric creature.