Home » Symptoms » Dog Symptoms A-Z » Inflammation of the third eyelid (nictitans)

Inflammation of the third eyelid (nictitans) in Dogs

Author: Dr. med. vet. Gisa Löwe | Last modified: 17.02.2026

When to visit the vet?

Non-urgent see a veterinarian within 2–3 days

ORANGE/RED for significant Pain, suspected corneal clouding/ulceration, purulent discharge, visible mass/prolapse, or worsening vision.

Unsure about what’s wrong with your pet? Feel free to use our Symptom Checker for more clarity

Definition

Inflammation of the third eyelid, also known as nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. inflammation or protrusion, is a condition where a dog’s third eyelid appears swollen or red. This inflammation can affect vision and is often a sign of an underlying health issue.

Can Occur with the Following Diseases:

Keratitis Pigmentosa (German Shepherd Keratitis, KSC, Pigmented Cornea)

Basics and possible causes

The third eyelid, also called the nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye., is a thin membrane located in the inner corner of the eye. It protects the eye, distributes tear fluid, and removes foreign bodies. In dogs, this membrane can become irritated or inflamed due to various factors.

One of the most common causes of third eyelid inflammation is an infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease.. Bacterial or viralViral refers to viruses and their effects on the organism. Viral infections in dogs and cats can range from harmless colds to severe, life-threatening diseases. infections can triggerA trigger is a stimulus that elicits a specific reaction or state. In veterinary medicine, this can refer to emotional responses, such as fear or aggression, or medical conditions, such as seizures in dogs and cats. an inflammatory response, leading to swelling and redness. Parasites, such as worms or mites, can also cause inflammation by triggering irritation or secondary infections.

Allergic reactions are another cause of third eyelid inflammation. Dogs can be sensitive to environmental allergens like pollen, dust, or mold, which leads to eye inflammation. Allergic reactions to food or medication can also manifest as nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. inflammation.

Mechanical irritation, such as foreign bodies in the eye or the dog rubbing its eye, can also irritate the nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye.. Additionally, systemic diseases like autoimmune disorders or tumors near the eye can cause inflammation of the third eyelid.

Typical accompanying symptoms

Swelling: A clear thickening of the nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. that goes beyond the normal state.
Redness: The nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. can be very red, indicating inflammation.
Discharge: Often a clear, yellowish, or purulentPurulent refers to pus or the production of pus, which may indicate a bacterial infection. Purulent inflammatory conditions are often painful and may have significant swelling and redness. discharge occurs from the affected eye.
Increased blinking or squinting: The dog may blink more often or walk with a closed eye to relieve the irritation.
Rubbing the eye: Dogs often rub with their paw or on objects to relieve the Itching, which can make the problem worse.
Behavioral changes: The dog may appear restless or irritated due to the persistentPersistent means lasting or continuing for an extended period. In veterinary medicine, it can refer to chronic diseases or symptoms that do not subside. discomfort.
Decreased vision: In severe cases, the dog’s vision may be impaired.

When to see a vet?

A visit to the vet is necessary if the third eyelid inflammation does not subside on its own within a day or if symptoms increase. Inflammation accompanied by discharge or severe itching should also be examined by a vet immediately.

A vet visit is especially important if the dog shows signs of Pain, such as persistentPersistent means lasting or continuing for an extended period. In veterinary medicine, it can refer to chronic diseases or symptoms that do not subside. crying, Restlessness, or avoiding being touched on the head. If the affected eye is kept closed, this is also an indicationIndication refers to a valid reason or rationale for using a specific treatment, medication, or medical procedure. It is based on the diagnosis and the patient's clinical condition. that a more serious examination is needed.

If the dog shows symptoms of a systemic illness, such as Fever, lethargy, or loss of appetite, a vet should also be consulted immediately. These signs may indicate that the third eyelid inflammation is only a symptom of a larger health problem.

Symptom recognition for the pet owner and veterinary diagnostic procedure

It is important for pet owners to check their dog’s eyes regularly to detect changes early. Look out for Swelling, redness, or unusual discharge. Your dog’s behavior can also provide clues; if they blink more often, rub their eye, or seem irritated, an inflammation might be present.

The vet will first perform a thorough examination of the affected eye. This includes checking the nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. for Swelling, redness, and discharge. The vet may also use an ophthalmoscope to examine the internal structures of the eye and determine if foreign bodies or ulcers are present.

To rule out infections, a sample of the eye discharge may be taken and tested in a lab for bacteriaBacteria are microscopic, single-celled organisms that exist in almost every environment on Earth. Some types of bacteria are beneficial or even essential to life, while others can cause disease. or viruses. AllergyAn allergy is an overreaction of the immune system to a normally harmless substance, the allergen. The reaction can include symptoms such as skin rash, itching, sneezing, respiratory distress, or in severe cases, anaphylactic shock. tests or blood tests may also be necessary to identify the cause of the inflammation. In some cases, an ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. or an X-rayX-ray is an imaging technique that uses X-rays to create images of the inside of the body. It is often used to diagnose bone fractures, lung diseases, and other conditions. may be required to diagnose underlying issues.

What the pet owner can do and professional therapy options

Before starting treatment, it is important to wait for the vet’s instructions, as incorrect measures could worsen the situation. However, there are some general steps pet owners can take to relieve symptoms while waiting for a veterinary diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients..

Keep the area around the eye clean by gently wiping it with a clean, damp cloth to remove discharge. Be careful not to use any harsh or irritating substances that could worsen the inflammation.

Prevent the dog from scratching or rubbing the eye by using a protective collar if necessary. This helps prevent further irritation or injury. Ensure the dog stays in a quiet environment to minimize stressStress refers to the state of an organism reacting to external stimuli or demands. In veterinary medicine, stress can have physical or psychological effects on animals, impacting their health and well-being., which could worsen the symptoms.

Make sure your dog is well-hydrated and has access to fresh water to support overall health and prevent dehydration, which could worsen symptoms. It is also advisable to check your dog’s diet and ensure they receive all necessary nutrients to strengthen the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body..

Avoid using home remedies or over-the-counter medications unless specifically recommended by a vet. These can often do more harm than good, especially if they are not intended for use on the eye.

Outlook on current research

Inflammation of the third eyelid, also known as nictitating membrane inflammation, is a symptom that occurs relatively often in dogs. Current research focuses on understanding the exact mechanisms that lead to this inflammation, as well as developing new and effective treatment methods. Nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. inflammation is often observed as a secondary symptom in other conditions like conjunctivitis or dry eyes. Scientists are investigating how inflammatory processes in the eye are influenced and what role the dog’s immune responseAn immune response is the immune system's reaction to foreign substances (antigens), such as microorganisms or proteins. It involves a series of processes aimed at recognizing, fighting, and eliminating these antigens. plays.

Another focus of research is genetic predispositionA predisposition is an innate inclination or susceptibility of an organism to certain diseases or conditions. In dogs and cats, there may be a genetic predisposition to certain conditions such as hip dysplasia or certain heart diseases.. Some dog breeds show a higher susceptibility to eye problems, including inflammation of the third eyelid. Scientists are trying to identify genetic markers that could indicate a predispositionA predisposition is an innate inclination or susceptibility of an organism to certain diseases or conditions. In dogs and cats, there may be a genetic predisposition to certain conditions such as hip dysplasia or certain heart diseases. for this type of inflammatory conditions. Such findings could make it possible to develop targeted preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. strategies or optimize the breeding of such breeds.

New treatment approaches are also being studied, including the use of anti-inflammatory eye drops specifically aimed at relieving nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. inflammation. Researchers are also testing the effectiveness of natural remedies, such as certain herbal extracts with anti-inflammatory properties. InitialInitial means beginning or at the start. In medicine, it can refer to the first symptoms of a disease or the first phase of a treatment process. results are promising but also show that further clinical studies are necessary to ensure the safety and effectiveness of such treatments.

Another exciting area of research deals with the role of the eye’s microbiota. It is being investigated how the microbial balance on the eye surface influences the development of inflammation. The findings could lead to the development of probiotic treatments that restore the balance of the microbiota and thus minimize inflammatory processes.

Finally, it should be mentioned that the importance of interdisciplinary approaches in research is increasing. Veterinarians, geneticists, and microbiologists are working together to develop a more comprehensive understanding of the factors that lead to third eyelid inflammation. This collaboration could lead to innovative, multidimensional treatment strategies in the future.

Frequently asked questions

1. What is the function of the third eyelid in dogs?

The third eyelid, also called the nictitating membrane, has the task of protecting and moisturizing the eye. It helps remove foreign bodies and dirt from the eye and contributes to the even distribution of tear fluid.

2. How do I recognize Inflammation of the third eyelid (nictitans) in my dog?

Inflammation of the third eyelid can be recognized by redness, Swelling, and increased tearing of the affected eye. Sometimes, a yellowish or greenish discharge also occurs. The dog may also blink more often or rub its eye.

3. What causes Inflammation of the third eyelid (nictitans)?

Inflammation can be triggered by various factors, including infections, allergies, foreign bodies in the eye, or systemic diseases. Injuries or irritations of the eye can also lead to inflammation.

4. How is Inflammation of the third eyelid (nictitans) diagnosed?

Diagnosis is usually made through a thorough eye examination at the vet. They will examine the eye for signs of inflammation, infection, or foreign bodies. In some cases, additional tests such as a swab or a blood test are necessary.

5. What treatment options are available for an inflamed nictitating membrane?

The treatment depends on the cause of the inflammation. Anti-inflammatory eye drops or ointments are often prescribed. For bacterial infections, antibiotics may be necessary. In severe cases or if there are foreign bodies in the eye, surgery may be required.

6. Can Inflammation of the third eyelid (nictitans) heal on its own?

In some cases, a mild inflammation can subside on its own, especially if it was caused by short-term irritation. However, for persistent or severe symptoms, a vet should always be consulted to avoid complications.

7. How can I prevent Inflammation of the third eyelid (nictitans) in my dog?

Regular eye care, such as cleaning dirt and tear stains from the eye area, can help prevent inflammation. Additionally, potential irritants like dust or harsh cleaning agents should be avoided. For susceptible breeds or dogs with known allergies, targeted prevention with supportive care products can be useful.

8. Are there certain breeds that are more susceptible to nictitating membrane inflammation?

Yes, some breeds, such as the Cocker Spaniel, Beagle, or Shar-Pei, are more prone to eye problems, including third eyelid inflammation, due to their anatomical features or genetic predisposition.

9. Can Inflammation of the third eyelid (nictitans) affect my dog's vision?

Temporary inflammation usually does not affect vision. However, with chronic or untreated inflammation, the risk of serious eye diseases can increase, which could ultimately affect vision.

10. When should I take my dog to the vet?

If you notice signs of third eyelid inflammation, such as persistent redness, Swelling, or discharge, you should see a vet. Early diagnosis and treatment can help avoid complications and preserve your dog's eye health.