Dogs are similar to humans in many different ways but not in the case of sleep, though. Some of the breeds sleep with their eyes open. If you find your dog sleeping with his eyes open, need not be alarmed as it is how he falls asleep. It mainly depends on the breed whether they sleep with fully opened or semi-opened eyes. In order to know why they do so, you need to have a look at a dog’s anatomy.
What you see is not what it is in real
If you wonder why dogs do not shut their eyes during sleep, you are wrong. What you see open is a third eyelid which dogs possess. You will get to know this if you take a closer look at your dog while he is asleep. Yes, unlike humans, dogs do have a third eyelid which is basically a membrane to keep the eyes moist. This third eyelid also is known as palpebra tertia acts as a protective shield and is partially responsible for tear production.
The Function of the third eyelid
The third eyelid, also called the nictitating membrane, is a skin fold using the dog to open and close the eyes voluntarily. Dogs have an upper and lower eyelid along with an extra eyelid which situates in the inner corners under the lower eyelid. The primary function of this third eyelid is to protect the eyes by clearing off mucus and dust particles.
It also contains lymphoid tissues, which produce antibodies that are responsible for the immunity of a dog. In short, the third eyelid also acts as a lymph node to protect the dog from infection. It also can project the cornea from injuries just like in humans. The nictitating membrane also keeps their eyes moist all the time, so they do not have to blink their eyes if exposed to dust.
Do only dogs have a third eyelid?
Dogs are not the only animals which have a third eyelid. Cats, fish, camels, birds and some of the reptiles also have a third eyelid. This extra eyelid turns to be useful when hunting for food because they would never miss a pray. However, the third eyelid is not visible in most of the animals the way that you can see in dogs.
When does the third eyelid become visible?
When the dog is asleep, his both eyes are closed and in order to perform the functions of protection and moisturizing the third eyelid gets visibly opened. When the dog wakes up, the nictitating membrane must retain back to its old form tucked into the inner corner of the eye. Generally, the third eyelid becomes visible only when there is any illness or injury if the dog is awake.
Watch the video for dog dreaming with nictitating membrane:
When you need to be alarmed
Although the third eyelid is useful in terms of the purpose it serves, a visible third eyelid can also be an indication of some disease. It can be a loud symptom of a disease called “Cherry eye.” The condition is when the supporting cartilage of the eyelid folds over, and it thereby loses its protective power. When the gland exposed to dirt, the chances of infection are high. You need to take your dog to a vet immediately because it is a painful condition.
Lagophthalmos is another condition, which is the incapability to close the eyelids completely. The disease is prominent in most of the breeds of dogs and cats. If your dog is suffering from such a condition, you will be able to see a small opening between the eyelids when your pet is asleep.
As the third eyelid serves a lot of important functions, any issues will lead to severe damage to your dog’s eyes. Ulcers can be very painful and leads to extreme dryness of the eyes. In severe cases, your pet will not be able to open his eyes for a long time. There are treatments for Lagophthalmos, and you can treat him with canthoplasty surgery. It is one of the effective treatments, and before any chronic irritation happens, you need to start the treatment.
You need to be highly observant about the third eyelid for your dog. If you feel your pet is suffering from any odd situations, do talk with your vet.
So, do dogs close their eyes while they sleep? The answer is, it depends on the breed of the dog. Some dog may sleep with their eyes closed and some do not. When you see, if your dog is sleeping without closing his eyes, there is nothing to worry. Your dog might be able to sleep by keeping his eyes open. It could be partially open or fully open or fully closed. That is their natural way of sleeping.