A dog’s third eyelid is the pink to white membrane that lives in the inner corner of both eyes and helps protect and lubricate the eye. Integrative veterinarian Dr. Julie Buzby explains third eyelid anatomy and what to do if your dog’s third eyelid is sticking up. Plus, she covers seven third eyelid problems in dogs.
Humans have upper and lower eyelids that help protect the eyes from dirt, debris, and bright light. Dogs (and cats), however, also have a bonus third eyelid as an extra layer of protection.
Under normal circumstances, a dog’s third eyelid stays tucked almost out of sight. However, under certain conditions, it may become elevated and/or look abnormal. This can signal an underlying issue.
What is the third eyelid in dogs?
The third eyelid (nictitating membrane) is a thin, pinkish-white membrane that is hidden under the lower eyelid in the corner of the eye closest to the nose. Its jobs are to:
- Slide horizontally across the eyeball for additional protection against dust and scratches
- Wipe debris off the surface of the eye
- Distribute the tear film to keep the eye lubricated
- House the gland of the third eyelid (a tear gland)
You could think of the third eyelid as both a windshield wiper (or squeegee) and a retractable cover for the eye. Plus, the third eyelid even contains a source of “windshield washing fluid” in the form of tears.
Third eyelid anatomy
The anatomy of the third eyelid allows it to carry out important functions. The inner and outer surfaces of the third eyelid are covered with conjunctiva. This is the same pinkish white tissue that lines the upper and lower eyelids and reflects onto the surface of the eye. Many dogs, but not all of them, will have darker pigmentation along the visible edge (leading edge) of the third eyelid.
Inside the conjunctiva sandwich sits a T-shaped piece of cartilage. It helps give the third eyelid enough rigidity to push debris and tears across the surface of the eye. This is sort of like having a mini squeegee inside the third eyelid. The squeegee portion lies along the leading edge of the third eyelid, and the handle extends backward toward the corner of the eye.
The gland of the third eyelid is tucked under the third eyelid at the base of the “handle” portion of the cartilage. By contributing 30-60% of the fluid portion of tears, the gland of the third eyelid plays an important role in tear production.
Can you see a dog’s third eyelid?
In the normal eye of an awake dog, the third eyelid is barely visible as a sliver of pink to black flat tissue resting against the inner edge of the eyeball. Unless you are looking closely, you may miss it entirely.
Some dog breeds, such as Pugs, Boxers, English Bulldogs, French Bulldogs, and Boston Terriers, may naturally have more prominent third eyelids. In other dogs, it is much harder to see.
If you’ve spent any time looking at your dog’s eyes, you probably have a good idea of how much of his or her third eyelid is normally visible. That is important when it comes to detecting problems with the third eyelid.
Times when it is normal to see more of the third eyelid
There are some situations where it can be normal for a dog to have the third eyelid showing. For example, you may see a bigger wedge of the third eyelid in a relaxed or sleeping dog. During moments of stress or excitement, the third eyelid can also sometimes appear briefly as your dog’s eyes move around.
Finally, the third eyelid can slide across more of the eye when it needs to protect the eyes (such as when dirt blows around or your dog is running through sticks).
Is it bad if my dog’s third eyelid is showing?
In general, noticing your dog’s third eyelid showing more than is normal for him or her (and at times not associated with sleeping, excitement, or a need for eye protection) may indicate an abnormality. This is especially true if your dog’s third eyelid is up for an extended period of time or if you notice additional symptoms.
What are the symptoms of a third eyelid problem?
Dogs with third eyelid issues can have a variety of additional symptoms, depending on how the condition affects the eye. Some of the more common ones include:
- A bright pink or red lump of fleshy tissue in the inner corner of your dog’s eye
- Increased third eyelid visibility (covers more of the surface of the eye than normal)
- Third eyelid looks red, bumpy, or swollen
- Excessive tear production, which may cause the fur around the eye to look wet
- Abnormal discharge that is yellow or green in color and may be watery or mucoid (goopy eye in dogs)
- Dried discharge around the eyes, which makes them look crusty
- Redness or swelling of the tissue of the upper and lower eyelids
- Squinting or holding the eye closed due to pain and inflammation
- Pawing at the eyes, which is also an indicator of irritation and pain
When should you take your dog to the vet?
Especially if your dog’s third eyelid is up and the eye is red, painful, or cloudy, you need to make an appointment with your vet quickly. However, even if you think the eye doesn’t look too bad otherwise, it is still important to reach out to your vet for cases of sustained third eyelid elevation.
Depending on the severity of your dog’s symptoms and which symptoms he or she is displaying, the vet may recommend a regular office visit or an emergency vet visit. In some cases, eyes can worsen quickly, so it is best to seek veterinary attention promptly.
What can I expect at the vet visit?
If your dog shows symptoms that could indicate a third eyelid condition, your veterinarian will start with a comprehensive physical exam. Sometimes the vet reaches a diagnosis based on the exam alone. But often he or she will recommend additional testing to gather more information. This may include:
In-depth eye exam
Your veterinarian may use a light to examine your dog’s pupils, checking both their size and response to light. Plus, he or she will evaluate the surface and interior of the eye with a hand-held ophthalmoscope. These parts of the eye exam help detect underlying eye problems, inflammation, or neurological issues that could affect the third eyelid.
Fluorescein staining
To check for corneal ulcers in dogs with an elevated third eyelid, the vet may apply a fluorescein stain. This yellow stain sticks to areas where the corneal surface is broken. Since third eyelid problems can be caused by corneal irritation, and since dogs may scratch the cornea when rubbing at an uncomfortable eye, knowing whether or not an ulcer is present is important.
Schirmer tear test
A Schirmer tear test measures a dog’s tear production by placing a tiny strip of special paper under the lower eyelid. This aids in diagnosing dry eye in dogs (low tear production), which can be a consequence of some third eyelid problems.
Tonometry
The vet may measure the intraocular pressure with a tonometer to screen for glaucoma in dogs (high pressure) or uveitis in dogs (a cause of low pressure).
Referral to a veterinary specialist
In some more complex cases, the vet may recommend that your dog see a veterinary specialist, such as a board-certified veterinary ophthalmologist. This can help ensure your dog’s eyes receive the best possible treatment.
What is the treatment for third eyelid problems in dogs?
Once the vet reaches a diagnosis, he or she will make treatment recommendations. Since a wide variety of conditions can cause a dog’s third eyelid to be elevated and/or appear abnormal, treatment can range from surgery to topical medications or managing another underlying condition.
7 reasons a dog’s third eyelid is showing
The following seven eye conditions may all cause your dog’s third eyelid to be elevated or look abnormal.
1. Cherry eye (prolapsed gland of the third eyelid)
Third eyelid gland prolapse (more commonly referred to as cherry eye in dogs) is the most common cause of an abnormal third eyelid. It can occur because the third eyelid attachment weakens and the tear gland pops out of place. While it can happen in any dog, some dog breeds, including Bulldogs, Beagles, Shih Tzus, Cocker Spaniels, Boston Terriers, and Pugs, are genetically predisposed to cherry eyes.
A prolapsed gland of the third eyelid is visible at the inner corner of the eye as a pink or red bubble, which looks a bit like a cherry, hence the name. The bump formed by the gland protrusion can vary in size and may even cover part or all of the eyeball. Additionally, you might notice redness to the eye itself, clear to cloudy eye discharge, and squinting. Occasionally, dogs with a cherry eye will also develop painful corneal ulcers in the same eye.
Historically, vets would surgically remove the whole gland to address cherry eye. However, that method has fallen out of favor because removing the tear gland reduces tear production and can lead to keratoconjunctivitis sicca (dry eye). Replacing the gland in its correct anatomic location is currently the treatment of choice in most situations because it helps maintain adequate tear production.
2. Horner’s syndrome
Horner’s syndrome in dogs occurs due to dysfunction of the portion of the sympathetic (“fight or flight”) nervous system controlling the eye and surrounding facial tissues. Due to loss of nerve signals, the dog may have:
- An elevated but otherwise normal-looking third eyelid
- Sunken eye
- Drooping eyelid
- Constricted pupil
While it more commonly just affects one side of the face, Horner’s syndrome can occasionally occur in both sides at once.
Horner’s syndrome isn’t a disease itself. Rather, it is a symptom that occurs as a result of conditions such as middle or inner ear infections, spinal diseases, and trauma or tumors affecting the neck, chest, or back. Interestingly, about half of the time Horner’s syndrome in dogs is idiopathic, meaning no cause can be identified.
The vet will address the underlying cause (if found) and support the dog while nerve function returns. Recovery can be slow, and the condition can take months to improve. But many cases of Horner’s syndrome resolve on their own and have a good prognosis.
3. Eye irritation and/or infection
Eye injuries, irritation, or eye infections in dogs can all cause redness and elevation of the third eyelid. Additionally, the dog may paw at the eye, squint, or hold the eye closed. And you might notice redness of the surface of the eye and inner eyelids, cloudy eyes in dogs, and eye discharge.
Some of the more common culprits are seasonal allergies in dogs, foreign objects in the eye (dirt, grass, hair, foxtails in dogs, etc.), corneal scratches or ulcers, and dry eye.
Treatment heavily depends on the cause of the irritation and/or infection. If an object is stuck in the eye, the veterinarian will work carefully to remove it. Otherwise, he or she will formulate a plan to manage the underlying condition, whatever it may be. To deal with the inflammation and/or infection, your dog may also need eye drops, anti-inflammatory medications, or antibiotics.
4. Dehydration or weight loss
Moderate to severe dehydration in dogs or weight loss can cause both eyeballs to sink back into the eye socket. When this happens, the third eyelid will passively slide across more of the eye. Typically, the third eyelid will remain elevated until the underlying problem is resolved.
If your dog is dehydrated or experiencing unexplained weight loss, please consult your veterinarian. These could be symptoms of a more serious condition that requires prompt intervention.
5. Tumor, infection, or inflammation behind the eye
A tumor, abscess, or inflammation (cellulitis) behind a dog’s eye could push the eyeball and third eyelid forward. In addition to the third eyelid being elevated and potentially irritated, the eye may be red and look like it is sticking out more than usual.
In some cases, the eyelids and tissue around the eye will be swollen, too. Or the dog might be painful when you touch the eye or try to open the mouth. If the tumor has extended upward from the mouth or nasal cavity, you may also see symptoms associated with nasal tumors in dogs or dog mouth cancer.
Treatment will depend on the underlying cause. The vet will drain an abscess, then start the dog on antibiotics and anti-inflammatories. In the case of a tumor, removing the eye and potentially following up with radiation and/or chemotherapy tends to be the most common approach. But a veterinary oncologist can help determine what is best for your dog’s situation.
6. Tumors of the third eyelid
While uncommon, dogs can develop benign or malignant tumors of the third eyelid. This can lead to swelling and elevation of the third eyelid. Sometimes you can see the tumor in the corner of the dog’s eye. Other times, the vet will need to put gentle pressure on the eyeball to raise the third eyelid or carefully pull the third eyelid forward to visualize the tumor. (Don’t try this yourself.)
According to a study in Veterinary Ophthalmology looking at 127 third eyelid tumors in dogs, the three most common third eyelid tumor types were adenocarcinoma (cancerous), adenoma (benign), and squamous cell carcinoma (cancerous).
Depending on the size of the mass and suspected identity, treatment may involve removing just the mass, removing the whole third eyelid, or removing all contents of the orbit. Plus, chemotherapy and/or radiation may be necessary.
7. Everted or scrolled cartilage of the third eyelid
Instead of lying flat against the eyeball, sometimes the cartilage in the third eyelid will bend or roll outward. This leads to a thickened third eyelid margin, which may look like it is flipped over. Scrolled or everted cartilage tends to occur in both eyes. And a little over half of the time, the dog will also have a cherry eye.
Most commonly, everted cartilage of the third eyelid occurs in young large-breed and giant-breed dogs such as:
- Great Danes
- St. Bernards
- German Shorthaired Pointers
- German Shepherds
- Dobermans
- Newfoundlands
- Cane Corsos
- Anatolian Shepherds
- Weimaraners
- Irish Setters
Sometimes the abnormal third eyelid is just a cosmetic issue, but in other cases, it can cause tearing and inflammation of the eye. If it becomes problematic, there are surgical procedures to address the scrolled or everted cartilage of the third eyelid.
Work with your vet if your dog’s third eyelid is showing
There are a variety of conditions that can impact the third eyelid position or appearance. And they range from cosmetic to serious. If you are noticing that your dog’s third eyelid is showing more than usual, looks inflamed, or you are seeing other symptoms, it is best to reach out to your vet promptly.
While it isn’t the case with all causes of third eyelid elevation, some eye problems can worsen quickly. So don’t delay in seeking veterinary attention. The sooner you and your vet get to the bottom of what is causing the third eyelid issue, the sooner your sweet pup’s eyes will start feeling better.
Has your dog’s third eyelid been elevated or abnormal?
Please comment below.
