Reptiles have some of the most exciting eyes in the animal kingdom.
You can discover pupils with round, elliptical, horizontal, and even star shapes between reptiles and amphibians.
Join us as we delve into the vision of reptiles and learn all there is to know about reptile eyesight.
Table of Contents
- Some reptiles are dichromatic – they can only see blue and green.
- Reptiles can usually see five colors, and some can see infrared.
- Pupil shapes vary in reptiles and are typically round, horizontal, or vertical.
- Reptiles use their Jacobson’s organ to help contribute extra detail to their vision (through scent).
- Some reptiles have a third or parietal eye, which contributes information to their nervous systems.
With so many types of lizards and reptiles, it’s impossible to cover all aspects of lizard vision at once.
Lizard eyes have a vast array of pupil shapes, some are lidded and others are lidless.
There are three different types of pupils in reptiles.
Round pupils are the most common pupil shape in the animal kingdom. Humans, fish, and birds have this type of pupil.
A rounded pupil is more receptive to light than a horizontal or vertical one. Animals that are usually active during the day tend to have this type of eye.
This eye formation is typical in reptiles that hunt actively in daylight hours.
Fun Fact: Some gecko species have rounded pupils, which can shrink to the size of pinpricks!
Rounded pupils give snakes and other hunters the ability to take in plenty of light from the sun and create clear images of what and where their intended prey is.
Round-pupil reptiles include:
- Turtles (yes, turtles are reptiles)
- The Boomslang (Dispholidus typus)
- Komodo Dragons (Varanus komodoensis)
While vertical pupils aren’t as common as round ones in the reptile kingdom, you’re more likely to see them than horizontal pupils.
Each pupil formation has a unique advantage. Vertical pupils give the ability to gauge distances.
Reptiles with vertically oriented pupils can estimate how far away something is.
You’ll see this type of eye more commonly in ambush predators, who can use the advantage of guessing how far away a prey item is.
It enables them to know exactly when to launch an attack.
Examples of vertical-pupil reptiles include:
- The Tokay Gecko (Gekko gecko)
- The Gaboon Viper (Bitis gabonica)
- Burton’s Legless Lizard (Lialis burtonis)
Horizontal pupils are common in animals that aren’t high up the food chain.
This eye configuration allows animals to receive light from both in front of and behind them, giving prey species the maximum amount of vigilance.
Lizards and snakes with this type of eye are generally on the constant lookout for the arrival of larger predators. It gives them almost a panoramic view of their surroundings.
This type of pupil is common in larger vertebrates, like goats and deer, as it allows them to look out for predators in most directions.
Reptiles with this type of eye include:
- Horny Toads (Phrynosoma spp.)
- The Green Vine Snake (Oxybelis fulgidus)
Reptile Eyes & Vision
Vision isn’t the easiest thing to explain as a rule, but you need at least some basic understanding of how eyesight works before talking about reptile vision.
In the simplest form, most animals (including humans) see by interpreting the light reflected from objects.
The molecular biology of the eye allows it to interpret light as images. Reptile and snake eyes have two major cell types which react to different light signals.
The two cell types are cone-shaped and rod-shaped. Rods pick up any visible light and signal the brain when they do.
Cone cells come in multiple variations, and each one responds to a different color.
When the cell encounters the right light color, it sends signals to the nervous system for interpretation.
Humans have three types of cones, which allows us to see red, green, and blue. In reptiles, most species have four cones, and some even have five.
The result? Reptilians can see all the colors we do and a range of colors that we CAN’T see. Some species (those with the fifth cone) can even see UVA rays.
As a result of their different cell construction, some of the snakes and their legged relatives can see much more than we can.
It depends on the species, though, and some may be blind.
Of course, this is the basic version of reptile eyesight and not approved by the academic press. Vision is a highly complex field, and there’s always more to learn.
Reptile Eye Anatomy
The lizard eye anatomy is similar to humans, despite the oddities in their vision. The eye has the following parts:
Eyelid – Besides snakes, most reptilians have eyelids that can blink to maintain moisture and protect the eye.
Fun Fact: Snakes, the gecko family, and some other types lack eyelids. They have an adapted transparent scale called a spectacle which protects the eye. When they shed, they shed the “eyelid” too.
Sclera – is the outside wall of the eyeball. It keeps the vitreous fluid (eyeball juice to you and me) inside, where it belongs.
Cornea – acts as an outer lens, provides up to 75% of the eyes’ focus, and is transparent.
Iris – a ring of pigmented muscles which control the size of the pupil.
Pupil – a hole in the sclera that either expands or contracts to let more light into the eye.
Lens – located behind the iris and pupil. All light passes through it on the way to the retina. The lens provides the rest of the eye’s ability to focus.
Retina – is the sensory layer that contains the sight cells. Without a functioning retina, a reptile would be blind. The retina is pigmented and lines the inside of the sclera.
The evolution of snakes and their kin hasn’t made it easy to notice any sign of their generally superior eyesight.
In most cases, they can see MORE of the light spectrum than humans and see better for catching prey.
Overall, they can understand more surface light reflections and have superior vision.
As with humans, the reptilian eye’s ability to interpret its surroundings comes from interpreting light waves that come through an outer lens, then an inner lens, before the retina interprets them.
In “lesser” animals, like insects, they manage to create a broad sense of vision through basic senses.
Can Snakes See Color?
Many people ask, “Can snakes see color?”
Snakes CAN see color, and most snakes can see more colors than humans can.
As mentioned earlier, the sensory layer of the eyeball has cells called cones and cells called rods.
Most reptilians in the world have four types of cones, which is one more than humans have.
Some of the creatures in this group can even see ultraviolet and infrared rays. In rare cases, some types may only have two cones and see like a colorblind person.
Do Lizards Have Eyelids?
Do lizards have eyelids? Unlike snakes, lizards usually have movable eyelids. This adaptation helps them to keep their eyes clean and protect them from harm.
Some reptilians, with geckos the most famous of them, lack movable eyelids, and their eyes have a transparent membrane for protection.
When creatures with these transparent membranes shed, the scale becomes opaque and obscures their vision.
Do Most Lizards Have the Third Eye?
Many of these animals have a third sight structure called a parietal eye. It isn’t a complete eye, but a basic one with a lens and a cornea.
The parietal eye is part of the epithalamus and can sense light and darkness. It helps the animal moderate hormone production and decide how much time to spend in the heat.
When it’s visible (which is rarely), it looks like nothing but a dimple in the skin.
This organ doesn’t give the creature vision but allows it to take in sensory signals.
Can Most Reptiles “See” With Their Tongues?
In humans, we rely on our eyesight for vision. For lizards, snakes, and other reptilians, there’s no better vision than that supported by their tongues.
You could say that snakes see by taste, though that wouldn’t be accurate.
If you’ve ever seen a snake hunting, or a water monitor doing its thing, you’ll have noticed the constant flick, flick, flick of its tongue.
Some people refer to this as tasting the air, though the reptiles use their tongues to pick up a scent.
Reptilians, amphibians, and mammals have an organ called the Jacobson’s or vomeronasal organ.
It takes its name from Ludvig Levin Jacobson, the Dutch anatomist who discovered it.
This unique anatomical development is a scent organ surrounded by many blood vessels and nerve endings.
In humans, it’s near the back of the nasal cavity. In reptiles, the organ is on the roof of the mouth.
In the course of their evolution, reptiles learned to rely on Jacobson’s organ.
First, they flick their tongues out to pick up a scent, then apply their tongues to the surface of the organ.
How does it help the vision of the reptiles, though?
The organ connects to the snake’s nervous system and provides details that the animal can add to the basic pictures that the reptile saw through sight.
We hope you’ve enjoyed this article about how reptiles see. Of course, there’s far more to learn about our scaly friends.
If you’d like to learn more, why don’t you check out our article about how long snakes live?
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