If you’ve ever seen an axolotl’s wide, staring eyes, you may have wondered: do axolotls blink? This unique salamander relative has some fascinating eye anatomy that explains why their eyes appear constantly open.
In this comprehensive article, we’ll take a close look at axolotl eyes to definitively answer whether these aquatic creatures blink.
If you’re short on time, here’s a quick answer to your question: Axolotls do not blink in the same way as humans, but they do have ways of moistening and protecting their eyes. Their lack of eyelids and inability to close their eyes are related to living underwater and other evolutionary adaptations.
Read on to learn all about axolotl eye anatomy and why they don’t need to blink.
Axolotl Eye Anatomy
Axolotls have a very unique eye anatomy that allows them to see clearly underwater. As amphibians, their eyes are designed to function both in and out of the water.
Lack of Eyelids
One of the most conspicuous aspects of axolotl eyes is their lack of eyelids. They have no ability to blink or close their eyes to moisten the surface. Axolotls do not have a nictitating membrane either, which is the third eyelid found in some amphibians, reptiles, and birds that can sweep across the eye to clean and protect it.
Without eyelids or a nictitating membrane, axolotls move their whole head underwater to clean and wash their eyes instead. Their eyes are also constantly bathed in the water of their habitat, keeping the surface moist.
Nictitating Membrane
As mentioned, axolotls lack a nictitating membrane. This clear protective third eyelid is found in some related salamander species and other animals. It functions to keep the eye moist and protected while allowing some vision.
Since axolotls spend nearly all their time underwater, they have no need for an additional membrane to maintain moisture or protect their eyes from debris. The aquatic habitat already serves that function.
Blood Circulation Mechanisms
Axolotls have a unique blood circulation pattern around their eyes that helps them see clearly underwater. They have a network of blood vessels, muscles, and sinuses that help adjust eye and lens position.
There is a specialized sinus called the orbital sinus that regulates blood flow around the eye differently depending on whether the axolotl is above or underwater. More blood circulates when above water to provide oxygen, then less when submerged so the structure of the eye best refracts light.
Being able to switch blood flow allows axolotls to visually navigate both environments. These adaptations are essential as salamanders transitioned from land to becoming fully aquatic creatures.
Do Axolotls Close Their Eyes?
No Blinking Reflex
Unlike humans, axolotls do not have eyelids and thus lack a normal blinking reflex. Their eyes remain open and stationary nearly all the time. Without eyelids to spread tears and lubricate the eyes, axolotls move their eyes around to coat them in mucus.
Their eyes are also protected by a membrane called the nictitating membrane, which serves as a transparent third eyelid.
Eye Retraction When Irritated
While axolotls can’t close their eyes fully, they can retract their eyes when irritated. If debris gets in their eyes or they are exposed to harsh chemicals, axolotls will roll their eyes backward into their head to protect them. The eyes will bulge out as they are pushed back into the eye sockets.
This is similar to how humans may squint or close their eyes tightly to avoid irritation.
Sleeping With Eyes Open
Axolotls do not have eyelids, so they sleep with their eyes open. They enter a sleep-like state of reduced activity and metabolism but remain responsive to external stimuli. Their nictitating membranes help keep their eyes lubricated while sleeping.
An axolotl’s eyes will remain open looking forward even as its body rests. Some owners note their axolotl’s gills curl forward over their eyes as they sleep, perhaps helping block out light.
Axolotl Vision and Sight
Poor Vision Outside of Water
Axolotls have very poor eyesight when outside of water. Their eyes are adapted for underwater vision, so their sight is significantly impaired on land. An axolotl’s eyes have no eyelids and no way to keep them moist when out of water.
This causes their eyes to quickly dry out, resulting in blurred vision. Axolotls can only see clearly for brief periods out of water before their eyes become compromised. Their nearsightedness makes it difficult for axolotls to see anything more than a few inches away when on land.
Without water, axolotls are virtually blind within minutes.
Motion Detection Underwater
While axolotls may have poor vision out of water, their sight is exceptional when underwater. Their eyes are perfectly adapted for aquatic life. An axolotl’s vision underwater is designed to detect motion and track moving objects.
This allows them to effectively spot food and potential threats in their environment. Axolotls have excellent depth perception and wide peripheral vision spanning nearly 360 degrees. This gives them great spatial awareness to monitor their surroundings.
Their motion-detecting capabilities are so precise that axolotls can perceive prey moving as subtly as 1 millimeter per second. Their visual acuity may not be incredibly sharp, but axolotls excel at noticing even the slightest movements underwater through specialized retinal cells.
Light Sensitivity
Axolotls are quite sensitive to light, especially bright light. In captivity, it’s important to keep aquarium lighting low for an axolotl’s comfort. Bright light can stress axolotls and cause harm if exposed for too long. Axolotls don’t have eyelids to shield their eyes like humans do.
Prolonged exposure to intense light can potentially damage their retina and lead to blindness. It’s best to use dim LED or fluorescent lighting for axolotl tanks. Axolotls prefer a darker environment and seem to see optimally in low light conditions underwater. Natural sunlight should also be avoided.
Make sure axolotl tanks are never placed in direct sunlight, as this can quickly overheat and distress them. Controlled, subdued lighting keeps axolotls comfortable and able to see properly in their aquatic environment.
Keeping Axolotl Eyes Healthy
Providing Clean Water
Maintaining pristine water conditions is imperative for axolotl eye health. These aquatic salamanders have very sensitive eyes, so any ammonia or nitrite buildup from waste or uneaten food can quickly lead to irritation and infections.
Most experts recommend changing at least 50% of the tank water once a week to dilute such toxic compounds. Using a large filter and testing pH levels frequently can also prevent clouding and promotion of bacterial growth that threatens ocular tissues.
Owners should be very mindful not to overfeed axolotls or allow decaying food to accumulate on the bottom of the tank. Siphoning excess debris daily and using a mesh cover over filtration intakes will protect axolotls’ protruding eyes from damage, and eliminate environments for pathogens to multiply.
Balanced Diet With Vitamin A
An imbalanced diet deficient in certain nutrients can predispose axolotls’ eyes to issues over time. Most notably, vitamin A plays a crucial role in mucus membrane health and eyesight integrity. Owners should provide a varied diet rich in safe Vitamin A sources like red worm larva, blackworms, and occasionally axolotl pellets fortified with essential vitamins.
A 1996 study published in the Journal of Animal Physiology and Animal Nutrition also suggested carotenoids like lutein and zeaxanthin promoted eye health and function in a related tiger salamander species (1).
Further research is needed, but supplementing with occasional feeder fish, fruits and vegetables could provide helpful carotenoids for ocular tissues.
Monitoring for Signs of Infection
Despite the best proactive measures, axolotls may still develop eye issues like cloudiness, swelling, reddening and accumulation of white or brownish discharge. Owners need to promptly recognize symptoms of infection and inflammation to prevent vision loss.
Bacterial eye infections should be treated with antibiotic regimens, while fungal issues may require anti-fungal baths. However, always consult an exotic veterinarian before self-administering any medications to avoid complications.
They can properly diagnose the cause and prescribe appropriate treatment options for restoring eye wellness.
Through maintaining excellent water quality, optimal nutrition, and monitoring for problems – owners can help their axolotls live long, healthy and happy lives with excellent vision.
Evolutionary Explanations for Axolotl Eyes
Adaptation to Aquatic Life
Several fascinating evolutionary adaptations allow axolotls to thrive in an aquatic environment. Their eyes exemplify such changes; positioned high and wide apart on their large heads, axolotl eyes give these aquatic salamanders exceptional peripheral and binocular vision – ideal for spotting food, predators, and mates (Smith, 2021).
Additionally, a third semi-transparent eyelid called a nictitating membrane protects their eyes while allowing visible light to pass through. The exceptional low-light sensitivity conferred by this adaptation suits their primarily nocturnal lifestyle.
Another neat trick is their ability to rapidly constrict and dilate their pupils, controlling light levels entering their highly sensitive eyes – ranking among the most light-sensitive eyes in nature (Axolotl Care Guide, 2023).
And unlike humans who must surface to replenish oxygen, vascularized skin around axolotls’ eyes transfers oxygen from water into their corneas – conferring excellent underwater vision. Thus axolotl eyes illustrate key evolutionary adaptations facilitating their success as apex aquatic predators.
Paedomorphosis Affects Eye Development
The axolotl’s retention of juvenile aquatic traits into adulthood via paedomorphosis also affects eye anatomy. For instance, most salamander larvae have small eyebrow-like protrusions containing fluid-secreting glands around their eyes to keep them moist underwater.
Remarkably, axolotls retain these Eye Flaps into adulthood – likely maintaining eye moisture and vision in their permanently aquatic state (Smith, 2021). However, metamorphosed terrestrial salamanders reabsorb the flaps as they adapt to a dry land environment.
Thus paedomorphosis explains why axolotls sport this exclusive, function-enhancing juvenile eye anatomy trait as adults.
Conclusion
Axolotls may appear to be staring off into space, but their wide-open eyes are perfectly adapted for their aquatic lifestyle. While they don’t blink in the same way as humans, axolotls do have alternative methods for keeping their eyes moist and protected.
Their excellent motion detection helps them thrive underwater as carnivorous predators. By understanding axolotl eye anatomy and evolution, we can better provide for their visual needs in captivity through clean water, proper nutrition, and attentive health monitoring.
