As many turtle keepers know, turtles have good eyesight and turtles are even capable of tracking and snatching quick prey underwater. As well as skillfully maneuvering around objects.
However, there is still a lot that most of us don’t know about turtle eyes. While we may never know exactly how colors appear to turtles, there are many questions we can easily answer with the evidence available to us.
Questions such as, “Can turtles see color?”, “How far can turtles see?”, “Can turtles see in the dark?”, “Can tortoises see in the dark?”, and “Can turtles see ultraviolet light?”
To understand how turtles see, we first need to consider how humans see so we can draw relatable comparisons which will help us understand how turtles see.
Humans see within the wavelength of about 400 nm to 740 nm. While different turtle species perceive different vision wavelength ranges, turtles are also sensitive to wavelengths of 400 nm to 740 nm, they seem to be more sensitive to shorter wavelengths such as those around 300 to 370 nm (which is within the wavelength range of ultraviolet light).
In fact, turtles’ eyes have UV receptors and turtles are capable of seeing colors that humans can’t imagine.
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Can Turtles See Color?
It used to be thought that turtles couldn’t see color and probably saw the world in greyscale.
This theory has been proven to be incorrect. According to research conducted, turtles can differentiate between several different colors.
They are particularly sensitive to shades of red and can differentiate between different shades of red better than humans do.
Owners have noticed that their turtles react to different colors in different ways. This is generally noticed in colors such as red, orange, and yellow, which seem to be their favorite colors.
Not only can turtles see color, but research also suggests that it’s likely that they can see a broader spectrum of colors than humans.
According to a study published in the Proceedings of the Royal Society B, reptiles such as turtles and even birds see red differently than what people do.
In fact, a gene (CYP2J19) which can be traced back to dinosaurs allows birds and turtles to see more shades of red than humans can. As such animals can pick up shades between crimson and scarlet.
Yellow & Orange
Several turtle keepers have noticed that their turtles have an odd attraction to the colors red, yellow, and orange. When they see objects of these colors, they would often investigate the object. According to Animal Planet, when a turtle does this, they want to find out if the object is edible.
Can Turtles See In The Dark?
While turtles can see in the dark just like humans can, they don’t have excellent night vision. Just like humans, during the day, the iris narrows and the pupil constricts.
This allows less light in and ensures that our eyes aren’t overwhelmed by the amount of light they receive. When it’s dark/or there is less light, the pupils of the turtle enlarge to allow in more light.
This allows turtles to see in the dark. While turtles can see in the dark, their eyes need time to adjust when it goes dark all of a sudden. After that, the turtle can see pretty well. As such, don’t be surprised when you see your turtle moving around its tank at night.
Turtles like humans lack tapetum lucidum. This is a layer of tissue in the eyes of several vertebrates such as dogs, cats, lemurs, deers, and many more.
The tapetum lucidum reflects light that enters the light back onto the retina and allows nocturnal animals such as owls, wolves, cats, and many more to see better in the dark.
The tapetum lucidum allows animals such as cats to be 44% more sensitive to light and as such allows them to see light so dim that it’s imperceptible to humans.
Turtles Vision Underwater and on Land
Most turtles are either semi-aquatic or aquatic. Aquatic turtles spend most of their lives underwater. The only time they come out of water is to breathe, bask on rocks and logs on the water, or in the case of sea turtles to lay eyes on the shores.
As such, it is essential that they see underwater. Also, because they need to come up for air and also to bask, they need to be able to see out of water as well. The turtle’s eyes are well adapted to see both in water and air.
How Do Turtles See Underwater? (Anatomy of Turtle Eyes)
The curved nature of the human cornea refracts light and ensures that we see perfectly in the air. However, when underwater, the cornea is unable to refract light.
This is why our underwater vision is murky and unfocused. Aquatic animals such as fish rely solely on their lenses to refract light with their cornea acting merely as a protective barrier.
Unlike humans and fish, turtles need to be able to see clearly both underwater and out of water. They accomplish this by having flat corneas and spherical lenses. As such they have perfect vision underwater and can see quite well out of water.
Turtles have an even distribution of rods and cones. This makes their eyes best adapted for bright light. It, therefore, comes as no surprise that turtles are primarily diurnal creatures.
However, research and studies have suggested that sea turtles can see bioluminescence in their prey. This ensures that they can locate bioluminescent prey deep underwater.
How Far Can Turtles See?
Turtles are far-sighted underwater but near-sighted out of water. Most turtles are aquatic species and as such hunt underwater. This requires excellent underwater vision.
Which in turn means that turtles have flat corneas and spherical lenses. These features ensure that aquatic turtles can see far underwater. These same features mean that turtles are short-sighted out of water.
However, since turtles come out of water only to breathe in air and bask, they are quite okay with being short-sighted out of water.
Turtle Eye Problems
It’s necessary that you can recognize eye diseases in turtles and seek out treatment. Also, knowing the causes of eye problems ensures you can cut down the likelihood of eye problems as you can correct the causative factors.
The two main eye problems pet turtles suffer are eye infections and swollen eyes. When left untreated eye infections can lead to respiratory tract infection as the bacteria causing the eye infection can easily move to the nasal passages.
Respiratory tract infection can lead to death. As you can see, an eye infection is a serious health condition that can lead to death when left untreated. Swollen eyes make it hard for the turtle to see or eat. This too can lead to starvation and death.
Swollen eyes typically occur with an eye infection, and is an early sign of vitamin A deficiency. First of all, this deficiency causes the Harderian glands to swell up.
This is why the eyes become puffy. When left untreated, the eyelids become so puffy that the affected turtle can no longer open the eyes. At this point, the turtle is practically blind.
There are some symptoms of swollen eyes. If you notice any of these symptoms, you may want to get in touch with your veterinarian.
- Eyes may appear puffier than it usually is.
- The conjunctiva and tear-secreting glands redden in color.
- Swollen eyelids – the eyelids may be so swollen that the turtle is practically blind as it cannot see through the swollen eyelids.
- Excess tear production/ excessive weeping
- Difficulty breathing
- Turtles may stop eating and starve.
- Weight Loss
The main cause of swollen eyes is vitamin A deficiency, also known as hypovitaminosis A. vitamin A deficiency is down to unbalanced diets. Feed turtles a lot of leafy green vegetables.
Additionally, you can offer commercial turtle diets that contain all the needed nutrients, including vitamin A, in the right proportions. Other problems caused by vitamin A deficiency include swollen feet and kidney damage.
It’s important to ensure that your turtle is provided the right diet. Research the dietary needs of your turtle and feed it properly. A mix of commercial turtle diet and leafy green vegetables is the way to go.
Offer foods such as spinach, parsley, kale, dandelion leaves, romaine lettuce, curly green lettuce, squash, and zucchini.
Additionally, you can supplement the turtle’s diet.
You need to see a herp vet for prescribed treatment. Vitamin A injections and prescription vitamin A drops are usually used to treat swollen eyes. Additionally, the turtle owner needs to improve the turtle’s diet.
Because swollen eyes often go hand in hand with eye infections, the vet may also need to treat for bacterial eye infections.
Bacterial Eye infection
Bacterial eye infections are closely related to respiratory tract infections, as the same bacteria that cause eye infections also cause RTI (respiratory tract infection). As you may already know, respiratory tract infections can lead to death. The bacteria usually responsible for eye infections are Pseudomonas and Aeromonas.
Some symptoms of eye infections include –
- Reddening of the conjunctiva.
- Puffy eyes
- Discharge from eyes
- The turtle scratches and rubs the eye frequently.
Since eye infections are linked to respiratory tract infections, be on the lookout for RTI symptoms such as
- Discharge from the mouth, nose
- Loss of balance when swimming
- Wheezing/difficulty breathing
There are many causes of eye infections. However, the common causes include
- Unsanitary living conditions such as dirty aquarium water.
- Vitamin A deficiency.
- Poor temperature control.
Make sure that the aquarium water is always clean. Install a powerful aquarium filter marked for an aquarium which is twice the size of the turtle’s current aquarium. This is because turtles produce more waste than fish do.
Also, change about a third to half of the water in the aquarium every week. Also, perform nitrite and ammonia level tests on the water. If the levels remain below the recommended levels, then the turtle is safe,
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As with swollen eyes, you need to see a vet for treatment. Systemic antibiotics are used to treat eye infections.
Pet keepers also need to improve the living conditions of the turtle’s enclosure to prevent the illness from recurring.
Turtle eyes are perfectly adapted to the turtle’s environment. As such, they have excellent underwater vision and can see color. Turtles are even capable of seeing into the UV spectrum. Something humans can’t do.
Their excellent vision ensures that they can identify food, navigate their environment, and even locate mating partners. Turtles also suffer from eye problems, with the most common ones being eye infections and swollen eyes.
When left unchecked, these problems can lead to death. Prevention is always the best policy. To prevent eye infections and swollen eyes from occurring, ensure the enclosure, and the aquarium water is clean, and feed the turtle a well-balanced diet.
If you have any questions or information, kindly leave a comment.