What is the Third Eyelid in Dogs?

Dog third eyelid
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The world of dogs is full of unique anatomical peculiarities, one of which is the third eyelid. While we are all familiar with our own two eyelids, dogs have a third eyelid that serves a variety of critical purposes. In this detailed guide, we will delve into the realm of the dog third eyelid, exploring its purpose, causes of abnormalities, signs to watch for, and the appropriate treatments. Let us go on this illuminating trip to uncover the mysteries of the dog’s third eyelid!

What is the Dog Third Eyelid?

The nictitating membrane, often known as the haw, is a thin, translucent membrane located in the inner corner of a dog’s eye. Unless it covers a piece of the eye’s surface, it is not immediately noticeable. The third eyelid is found in many mammals, including dogs, cats, birds, and reptiles, and serves as a protective layer for the eye’s sensitive tissues.

Anatomy and Function of the Dog Third Eyelid

The third eyelid of a dog is made up of a cartilage-like structure covered by a thin coating of conjunctiva. It contains the third eyelid gland, often known as the Harderian gland, which produces a watery liquid that helps lubricate and protect the eye. The third eyelid serves as an additional barrier, protecting the eye from potential injury, foreign objects, and bright light.

Normal Function and Appearance of the Dog Third Eyelid

The dog third eyelid is normally buried in the inner corner of the eye, only becoming visible when it slides across the surface of the eye under particular conditions. This movement is usually smooth and rapid, indicating that everything is working well. The third eyelid may occasionally appear slightly pinkish or have a thin layer of mucus, which is considered normal.

Causes of Dog Third Eyelid Abnormalities

Despite its critical purpose, the dog third eyelid can occasionally exhibit anomalies. Various factors can contribute to these abnormalities, including:

#1. Cherry Eye:

Cherry eye, a condition in which the gland within the third eyelid protrudes and becomes apparent, is one of the most common issues affecting the dog’s third eyelid. The weakening of the connective tissues that support the gland is usually the source of this ailment. The actual source of this deficiency is unknown; however, it is thought to have a genetic component, with particular breeds, such as Bulldogs, Cocker Spaniels, and Beagles, being more inclined to cherry eye.

#2. Conjunctivitis:

Inflammation of the conjunctiva, the thin membrane that covers the eye and lines the eyelids, can also have an impact on the appearance and function of the dog’s third eyelid. Conjunctivitis can be caused by various reasons, such as viral or bacterial infections, allergies, irritants such as dust or smoke, or underlying medical disorders such as dry eye syndrome. Conjunctivitis is more common in dogs who have been exposed to environmental allergens or have a weaker immune system.

#3. Injuries and Trauma:

Traumatic occurrences, such as eye scrapes or blunt force trauma, can cause damage or displacement of the third eyelid, leading to abnormalities. The third eyelid can become inflamed, enlarged, or prolapsed as a result of scratches from other animals, foreign objects entering the eye, or hard play. Third eyelid anomalies caused by trauma require quick veterinarian intervention to avoid further difficulties and promote full recovery.

#4. Neoplasia:

Tumors or neoplasms can form in or around the third eyelid in rare situations, causing abnormal growths and alterations in appearance. A veterinarian must thoroughly examine and diagnose these tumors, which may be benign or cancerous. Early detection and treatment are critical for treating neoplasms of the third eyelid.

#5. Infectious Diseases:

Infectious disorders can also affect the health and function of the dog’s third eyelid. Canine distemper is a highly contagious viral disease that can cause conjunctivitis and impair the third eyelid. Other bacterial or viral infections, such as canine adenovirus or canine herpesvirus, can also lead to similar symptoms and abnormalities of the third eyelid.

#6. Autoimmune Disorders:

Autoimmune diseases like immune-mediated keratoconjunctivitis sicca (dry eye condition) can result in changes to the third eyelid. In many circumstances, the immune system incorrectly assaults the tear-producing glands, resulting in decreased tear production as well as inflammation and discomfort. In dogs with autoimmune illnesses, the third eyelid may seem dry, thickened, and inflamed.

#7. Age-Related Changes:

Age-related changes in the third eyelid of dogs are possible. These alterations can include an increase in the visibility of the third eyelid, a thickening of the membrane, or a decrease in the gland’s function. While these changes are typically regarded as normal, they must be regularly monitored, and veterinary help should be sought if any anomalies or discomfort are observed.

Signs of Dog Third Eyelid Abnormalities

It is critical to detect anomalies in the dog’s third eyelid to intervene quickly. Here are some warning indicators to look out for:

#1. Third Eyelid Visible:

When the third eyelid becomes apparent or protrudes more than usual, this is one of the most prominent indicators of a third eyelid anomaly. The third eyelid is normally hidden in the inner corner of the eye and is not visible. If your dog third eyelid is continuously visible, puffy, or inflamed, this could suggest an issue.

#2. Redness and Inflammation:

Dog third eyelid abnormalities may cause redness and irritation in the affected eye. The conjunctiva, which covers the third eyelid, can become inflamed and reddish. In some circumstances, the entire eye may appear bloodshot or reddish.

#3. Excessive Tearing:

Tear production may rise in dogs with third eyelid defects. Excessive tearing or a watery discharge from the afflicted eye may occur. This could be a result of the irregularity causing discomfort or inflammation.

#4. Blinking or Squinting:

Dogs who experience eye discomfort or pain as a result of third eyelid anomalies may squint or blink excessively. They may attempt to cover the afflicted eye by partially closing it or blinking fast. Squinting or blinking can indicate that your dog is in pain or is sensitive to light.

#5. Pus or Discharge:

If an infection or inflammation is causing the third eyelid anomaly, you might notice a discharge or pus coming from the affected eye. The discharge might be clear or hazy, and its consistency can vary.

#6. Changes in Eye Appearance:

The existence of a third eyelid anomaly might alter the look of the eye. The damaged eye may appear enlarged, puffy, or bulging. The abnormalities may also change the shape or position of the eye.

#7. Impaired Vision:

Your dog’s vision may be impacted, depending on the severity and underlying cause of the third eyelid anomaly. Dogs with poor vision may exhibit symptoms such as bumping into objects, hesitancy or difficulty navigating their surroundings or displaying uncoordinated movements.

It’s important to note that the signs and symptoms of third eyelid abnormalities can vary depending on the underlying cause. If you observe any of these signs or suspect an issue with your dog’s third eyelid, it is recommended that you seek veterinary attention. A thorough examination by a veterinarian can help determine the cause of the abnormality and guide the appropriate treatment.

Diagnosis of Dog Third Eyelid Abnormalities

If you feel your dog has a problem with their third eyelid, you must get veterinarian care for an appropriate diagnosis. To discover the underlying cause for the irregularity, a veterinarian will undertake a complete examination of the eye, including the third eyelid, using specialist equipment and techniques. Additional tests, such as ocular staining or culturing, may be performed to rule out infections or other underlying disorders.

Treatment Options for Dog Third Eyelid Abnormalities

The treatment choices for dog third eyelid anomalies are determined by the underlying cause and severity of the condition. Here are some examples of frequent treatment methods:

#1. Medical Management:

Your veterinarian may give topical ointments or eye drops to relieve inflammation, control infection, or lubricate the eye in cases of mild third eyelid abnormalities, such as conjunctivitis or moderate irritation.

If the anomaly is caused by a bacterial infection, antibiotics may be provided. To minimize inflammation and discomfort, anti-inflammatory drugs or corticosteroids may be utilized.

If the irregularity is linked to a systemic problem, such as dry eye syndrome, your veterinarian may recommend long-term care with drugs such as cyclosporine or artificial tears to enhance tear production and maintain eye health.

#2. Surgical Intervention:

Surgical correction is frequently required in cases of cherry eye, where the gland within the third eyelid protrudes. The surgical procedure involves repositioning the gland and anchoring it in the correct position. This aids in the restoration of the third eyelid’s normal function and look.

Tumors or neoplasms of the third eyelid may necessitate surgical removal. The scope of the operation is determined by the type of tumor and whether it is benign or malignant. Additional therapies, like as radiation therapy or chemotherapy, may be required in some circumstances.

Traumatic injuries or severe third eyelid prolapse may necessitate surgical intervention to repair damaged tissues and guarantee appropriate healing.

#3. Supportive Care:

Regardless of the underlying cause, supportive care is frequently required in the treatment of third eyelid anomalies. This may include cleaning the affected eye regularly to eliminate discharge or debris, maintaining a clean and pleasant environment to reduce irritants, and preventing the eye from future trauma or injury.
A protective collar (e-collar) may be recommended in some circumstances to prevent the dog from scratching or rubbing the affected eye.

#4. Follow-up Care:

Following initial therapy or surgery, regular follow-up meetings with your veterinarian are essential for monitoring the condition’s progress, assessing healing, and making any required revisions to the treatment plan.

Periodic eye examinations may be recommended by your veterinarian, particularly in cases of chronic illnesses or underlying systemic diseases, to guarantee long-term eye health and detect any recurrence or new abnormalities.

It’s critical to see a veterinarian for an accurate diagnosis and treatment options for your dog third eyelid anomaly. They will be able to assess the condition and recommend the best course of action to address the underlying cause and maintain optimal eye health in your canine companion.

Preventive Measures for Dog Third Eyelid Abnormalities

While not all dog third eyelid anomalies can be avoided, there are some precautions you may take to reduce your dog’s risk. A veterinarian’s regular eye examinations are critical for early detection of any issues and rapid action. Keeping the eye area clean and clear of irritants, avoiding trauma or injuries, and avoiding exposure to contagious eye diseases can all help lower the risks of having third eyelid difficulties.

How is a third eyelid prolapse treated?

Third eyelid prolapse, commonly known as nictitans gland prolapse or cherry eye, is often addressed surgically. The surgery’s purpose is to return the prolapsed gland to its usual place and secure it to prevent recurrence. The following is an overview of the treatment procedure:

  • Surgical Correction
  • Post-Surgical Care

It is crucial to remember that the surgical correction for a third eyelid prolapse might have varying degrees of success. Even after surgery, some dogs may experience a recurrence of the prolapse. Additional surgical procedures or alternative therapy methods may be considered in such circumstances.

Why is my dog’s third eyelid showing?

When a dog is under stress, dehydrated, or otherwise unwell, both third eyelids may be lifted. When the eye is uncomfortable due to a corneal ulcer, glaucoma, or dry eye, the third eyelid might be lifted. Also, When others see this, they frequently believe that the eye is “rolling back into the head.”

What is the purpose of the third eyelid in animals?

When the eye is at risk of being harmed, the third eyelid can also pop up swiftly and act as protection. The third eyelid also has more tear glands to assist in lubricating the eye and lymph tissue to help fight infection.

How do you check a dog’s third eyelid?

Pulling down the lower lid may reveal the third eyelid, also known as the nictitating membrane, which protrudes over the bottom inner corner of the eye. The third eyelid is often pale pink or white, with thin blood veins on the surface.

Do humans have a 3rd eyelid?

It’s actually the remnant of a third eyelid. It is vestigial in humans, which means it no longer serves its original purpose. Several more vestiges of our ancestor species are in the human body, gently riding along from one to the next.


The dog third eyelid, with its unique structure and protective role, is an essential component of a dog’s eye health. Understanding the causes, signs, and treatment options for third eyelid abnormalities is crucial for dog owners to provide timely care and ensure their furry friends’ well-being. If you notice any signs of third eyelid abnormalities in your dog, consult with your veterinarian for a proper diagnosis and appropriate treatment. With proper veterinary care and attention, your dog’s eyes can remain healthy and vibrant.

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