Why Is My Dog's Third Eyelid Showing?


Also known as the nictitating membrane or haw, the dog's third eyelid is something most owners aren't aware of until they see it for the first time.

All dogs have this membrane found in the inner corner of the eye but it is typically noticed only when it is drawn horizontally across part of the eye. Its color varies depending on the dog's breed and can range from clear to cloudy.

What Does the Third Eyelid Do?

Deborah S. Friedman, D.V.M. and diplomate with the American College of Veterinary Ophthalmologists has several explanations.

  1. The third eyelid acts as the dog's "windshield-wiper" for the cornea, effectively removing debris or mucus off of it.
  2. This membrane is responsible for producing about one-third of the dog's tears, since it has one of the most important tear glands attached at its base, and its lymphoid tissue acts like a lymph node producing antibodies to fight off infections.
  3. It also helps prevent injuries to the dog's cornea.

In dogs and cats, this membrane is not normally visible other than when the animal is sleeping or suddenly awakens from sleep. Indeed, if you lift the eyelid of a sleeping dog you'll likely see the whole eye covered by the third eyelid.

The dog in my pictures awakened suddenly after resting on my legs, and once she was fully awake, her third eyelid re-positioned normally.

However, the prolonged presence of the third eyelid, even when the dog is bright and alert, often denotes some sort of medical problem.

In the next paragraphs, we will see some common and not-so-common medical issues associated with the abnormal appearance of the dog's third eyelid.

Did you know?

According to Animal Eye Care LLC dogs have two tear glands in each eye; whereas, humans have only one. The orbital tear gland is responsible for producing 60 percent of tears and the third eyelid tear gland produces 40 percent.

The third eyelid should not be seen after the dog has awakened and is bright and alert.
The third eyelid should not be seen after the dog has awakened and is bright and alert. | Source

Reasons Why the Eyelid Might Be Showing

If your dog's third eyelid made a sudden appearance, you may be wondering what's going on. There are several possibilities that range from ocular problems to more systemic autoimmune or neurological disorders.

Eye Problems

Squinting along with the appearance of the third eyelid can be a sign of pain and some ocular issue.
Squinting along with the appearance of the third eyelid can be a sign of pain and some ocular issue. | Source
  • The presence of the third eyelid could be a sign that the dog's eyeball has sunken into its socket, often because of pain and inflammation. The third eyelid covers the eye to protect it from further injury, as in the case of corneal trauma.
  • It could also be that the structure meant to hold the third eyelid in place either weakened or got injured.
  • A further possibility may include allergic conjunctivitis.

Cherry Eye

Some dog breeds are prone to prolapse of a gland found in the dog's third eyelid, a condition known as "cherry eye" mostly because of its bright red presence resembling a cherry in the corner of the dog's eye.

This is a congenital disorder found commonly in certain dog breeds such as cocker spaniels, beagles, Boston terriers, and bulldogs.

What happens is the cartilage responsible for supporting the membrane folds over causing the third eyelid to no longer work well as a "windshield wiper." This results in a gland that is exposed and potentially inflamed.

Neurological Disorders

Some neurological diseases may cause loss of function to the nerve that supplies the third eyelid.

Horner's syndrome is a common neurological disorder that occurs suddenly and is characterized by sunken eye, droopy eyelids, droopy facial features, small pupil size, and the prolapse of the third eyelid.

Dilated blood vessels in the affected area cause owners to sometimes report that it feels warmer to the touch. The cause is unknown, but at times it can be triggered by trauma to the head, bite wounds, a herniated disc, a growth pressing on a nerve, a side effect of some medication, or a middle or inner ear disease.

While any dog can develop Horner's, golden retrievers and cocker spaniels are slightly predisposed. Other neurological disorders that can cause a third eyelid to be exposed include tetanus and dysautonomia.

Poor Physical Health

Certain physical conditions that are known for relaxing the muscles found around the eyeball and for causing the settling of the eye deeper into its socket may be a cause for the appearance of the third eyelid.

Dogs who are malnourished, dehydrated, who have lost weight or are generally not feeling well may manifest protrusion of the third eyelid.

Treatment varies depending on the cause. In some cases, a cause is never found. These are referred to as "idiopathic."

Sometimes the issue resolves on its own after several weeks. However, if it turns out to be an eye issue, as with all eye problems, it's best to see a vet, or better, a board-certified veterinary ophthalmologist immediately to prevent potential vision loss.

Questions to Ask

If you visit the vet or are trying to get a better idea of what's going on, here are some questions that can help you determine what's going on with your pet:

  • Did your dog bump its head? Or experience any other trauma? You might just need a cold compress on the eye for anywhere from a few to thirty minutes.
  • Is the eye okay aside from the third eyelid showing? In that case, and if both eyes don't also react similarly to light, there might be a cranial lesion.
  • Is your dog struggling to keep that eye open? This might indicate an eye injury.
  • Is there any discharge? This could be a sign of an eye infection.


If your dog's third eyelid appears abnormal, please see your vet immediately for diagnosis and treatment. This article is not to be used as a substitute for veterinary advice.

Alexadry © All Rights Reserved, Do Not Copy

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What a Third Eyelid Looks Like

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Comments 13 comments

ShyeAnne profile image

ShyeAnne 2 years ago from Deep Bay, British Columbia, Canada

Cool little piece of trivia I did not know. Voted up and Interesting!

Francesca27 profile image

Francesca27 2 years ago from Hub Page

I was wondering why our Akita had that! He has been gone for years. Thanks for the info.

grand old lady profile image

grand old lady 2 years ago from Philippines

My dog Ashley Pumpernickel had that. I never knew what caused it but this article helped me understand the third eyelid better. Eventually she needed an operation to have it removed.

alexadry profile image

alexadry 2 years ago from USA Author

Did she have cherry eye? I hope she is doing well after surgery, thanks for stopping by!

grand old lady profile image

grand old lady 2 years ago from Philippines

Yes, it was cherry eye. She recovered well, but she hates having her photo taken. Maybe it's because of the flash on her eye.

lisa 2 years ago

I got a puppy who was 10 weeks old. .. her third eyelid in both eyes has always been showing ... she's not in pain no discharge no smell no redness... any ideas??

alexadry profile image

alexadry 2 years ago from USA Author

I would get this checked out by the vet just to make sure.

Oneita 2 years ago

Our sheltie was recently diagnosed with Discoid Lupus. Does this cause the appearance of the 3rd eyelid & if so should it be treated?

alexadry profile image

alexadry 2 years ago from USA Author

According to the link below "DLE can also cause inflammation of the third eyelid." In this case, the underlying issue needs to be addressed.

Danise 6 months ago

My dog is 10 years old and her third eye is showing in both eyes. Could age be a reason for this. Is this painful?

Sam 6 months ago

My dog has just had a lump removed from his mouth and had an inner ear infection looked at too, ever since the op his third eyelids are visible

Would the op have caused this? He didn't have it before hand and will it clear up?

Thank you

alexadry profile image

alexadry 6 months ago from USA Author

It's difficult to say if it's painful as it depends on the underlying cause. Age may be a culprit indirectly, meaning that older dogs are more prone to having certain medical conditions that may cause it, best to see the vet.

alexadry profile image

alexadry 6 months ago from USA Author

The surgery could be a culprit if your dog is not feeling too well or is dehydrated. Whether it clears up or not depends on the underlying cause. I would mention it to the vet that did the surgery.

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