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Third Eyelid Swollen in cats

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

When to visit the vet?

Urgent see a veterinarian within 24 hours

Severe pain, corneal opacity/injury, vision loss, severe swelling/prolapse

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Definition

The third eyelid, also known as 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 in the cat’s eye that moves from the inner corner of the eye across the eyeball. A swelling of this third eyelid can indicate various health problems.

Can Occur with the Following Diseases:

Basics and possible causes

The third eyelid plays an important role in protecting the eye and distributing tear fluid. It can become inflamed or swollen for various reasons. A common cause 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. or inflammation of the eye, which leads to irritation and subsequent swelling of the third eyelid. Allergies triggered by environmental factors or certain foods can also cause swelling.

Another possible problem is Cherry Eye, a condition in which the gland of the third eyelid protrudes and swells. Although this condition is less common in cats than in dogs, it can still occur and cause significant swelling.

Injuries or a foreign body in the eye can also irritate the third eyelid and cause it to swell. In rare cases, tumors in or around the third eyelid can also occur and cause swelling. Finally, systemic diseases, such as autoimmune diseasesAutoimmune diseases are conditions in which the immune system mistakenly attacks the body's own cells or tissues as if they were foreign substances. Examples in dogs and cats include autoimmune hemolytic anemia and systemic lupus erythematosus. or severe infections, can affect the third eyelid.

Typical accompanying symptoms

Redness: A distinct redness of the third eyelid may indicate inflammatory conditions or irritation.
Tearing: Excessive tearing of the affected eye is often a sign of a problem with the third eyelid.
Pain: The cat may show signs of pain, e.g. by blinking frequently or rubbing the eye with its paw.
Decreased appetite: A cat with pain or discomfort in the eye may eat less.
Behavioral changes: ApathyApathy refers to a state of indifference and reduced interest or lack of emotional involvement in activities or events that would normally arouse interest. or avoidance of bright light may occur if the eye is irritated.
Changes in vision: In severe cases, vision may be impaired.
Pus or discharge: A yellowish or green discharge may indicate a bacterial 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..

When to see a vet?

A veterinarian should be consulted if the swelling of the third eyelid lasts longer than 24 hours or if the condition worsens. If the cat shows signs of severe pain or keeps the eye closed, an immediate veterinary examination is necessary.

An examination is also necessary if pus, bleeding, or a significantly worse general condition of the cat are observed. If a foreign body in the eye is suspected or if there is a sudden change in vision, a veterinarian should also be consulted immediately.

Symptom recognition for the pet owner and veterinary diagnostic procedure

It is important for the pet owner to observe the third eyelid regularly. A sudden swelling, redness, or increased discharge should be taken seriously. If the cat blinks frequently or rubs the eye, this may be 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. of a problem.

The veterinarian will first carry out a thorough examination of the eye, including the use of an ophthalmoscope to inspect the inner eye area. A fluorescein stain can be used to detect possible scratches on the cornea. 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. examination may be necessary to assess deeper structures of the eye.

If a systemic disease is suspected, blood tests can be carried out to identify inflammatory markerInflammatory markers are substances in the blood that increase in concentration when there are inflammatory conditions in the body. They help with the diagnosis and monitoring of inflammatory conditions in dogs and cats. or other anomalies. If a tumorA tumor is an abnormal growth of tissue that can be benign or malignant. Tumors can develop in any part of the body and affect various functions. cannot be ruled out, further imaging procedures such as a CT or MRI scan may also be necessary.

What the pet owner can do and professional therapy options

As a first measure, the pet owner can try to carefully rinse the cat’s eye with a sterile saline solution to remove possible irritants. However, this should only be done after consulting with the veterinarian in order not to worsen the situation.

It is important to prevent the cat from further irritating the affected eye. A neck brace or Elizabethan collar can be used to prevent the cat from rubbing its paw on the eye.

Feed the cat a hypoallergenic diet if an allergic reaction is suspected, and avoid contact with potential allergens. Make sure that the cat’s environment is clean and free of dust or other irritating substances.

Avoid using medications or eye ointments without veterinary advice, as some products may be unsuitable or even harmful to cats. Always consult a veterinarian before starting treatment.

Outlook on current research

Current research on the swollen third eyelid in cats focuses on better understanding the underlying mechanisms and developing effective 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. and treatment strategies. One focus is on identifying biomarkers that could help detect the condition early and distinguish it from other eye diseases. Researchers are particularly investigating the relationship between inflammatory conditions and the swelling of the third eyelid in order to develop targeted therapeutic approaches.

In the field of geneticsGenetics is the science of genes, heredity, and the variation of organisms. It studies how genetic information is passed from generation to generation and how it influences the development, appearance, and behavior of living things., it is being investigated whether certain breeds are more susceptible to swelling of the third eyelid. This could help develop preventive measures for affected breeds. 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. studies suggest that genetic predispositions may indeed play a role, which could lead to new opportunities in breeding and health monitoring.

Another area of research is the development of new topicalTopical refers to the direct application of medications or treatments to the skin or mucous membranes for a local effect, without being absorbed into the body. treatments that alleviate the symptoms while addressing the causes of the swelling. These include anti-inflammatory drugsAnti-inflammatory drugs are medications that reduce inflammation. They can be divided into nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids and are used in dogs and cats to reduce Inflammatory conditions and Pain. as well as innovative approaches such as nanoparticles that can specifically deliver drugs to the affected tissue. These approaches could reduce the need for systemic medications and thus minimize the risk of side effects.

In addition, the role of environmental factors, such as allergens and pollutants, on the third eyelid is being investigated. Researchers are trying to find out how these factors affect the swelling and whether changes in the environment can contribute to preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring.. Long-term studies could provide valuable insights here that go beyond eye health and promote general welfare strategies for pets.

There are also efforts to explore the role of the microbiome in connection with eye diseases. Scientists are investigating whether an imbalanceImbalance refers to an imbalance or disruption of normal function or composition in the body, which can lead to health problems. in the natural microbial flora around the eye could contribute to swelling of the third eyelid. Earlier studies in humans and other animals have shown that a healthy microbiome plays an important role in maintaining eye health, and similar findings in cats could open up new treatment approaches.

Research into imaging techniques is another exciting field. Advances in technology enable more detailed and less invasiveInvasive describes medical procedures or pathogens that enter the body or penetrate tissue. In medicine, invasive procedures can range from minimally invasive techniques to open surgery. examinations of the eye structure, which could lead to a more accurate 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.. These developments could make it possible to detect and treat swelling of the third eyelid early on, before serious complications arise.

Comprehensive epidemiological studies are helping to gain a better understanding of the prevalence and risk factors of swelling of the third eyelid in cats. Data from different geographical regions and populations can help to develop global health strategies and draw attention to frequently overlooked environmental factors.

Finally, the role of nutrition is also being investigated. Research aims to find out whether certain nutrients or diets can reduce the risk of swelling of the third eyelid. A balanced diet could play an important role in preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. by strengthening 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. and reducing inflammatory conditions.

Frequently asked questions

1. What is the third eyelid in cats?

The third eyelid, also called nictitating membrane, is a thin membrane that moves from the inner corner of the eye and protects and moisturizes the eye. It is usually not visible unless it is swollen or the cat is sick.

2. Why does the third eyelid swell in cats?

A swelling of the third eyelid can be caused by various factors, including infections, injuries, allergies, or systemic diseases. It is a symptom that can indicate various health problems.

3. Is a swollen third eyelid painful in cats?

Yes, it can be uncomfortable or painful for the cat, especially if it is accompanied by other symptoms such as redness, discharge, or itching. A veterinary examination is important to determine and treat the cause.

4. When should I take my cat to the vet?

If the third eyelid is swollen, especially if it is accompanied by other symptoms such as eye discharge, redness, or behavioral changes, you should see a veterinarian. An early diagnosis can prevent more serious problems.

5. Can I treat the swelling of the third eyelid in my cat myself?

It is not recommended to treat the swelling without veterinary advice. Incorrect treatments can worsen the situation or obscure the underlying cause. A veterinarian can provide the correct diagnosis and treatment.

6. What happens during the veterinary examination?

The veterinarian will examine the eye thoroughly, possibly perform a tear or Schirmer test, and check for signs of infections, injuries, or allergies. Depending on the findings, further tests such as blood tests or imaging procedures may be necessary.

7. How is a swollen third eyelid treated in cats?

The treatment depends on the underlying cause. It may include the use of eye drops or ointments, the administration of antibiotics or anti-inflammatory medications. In severe cases, surgical intervention may be necessary.

8. Can environmental factors influence the swelling of the third eyelid?

Yes, environmental factors such as dust, pollen, or chemicals can trigger allergies that lead to swelling of the third eyelid. Minimizing contact with such irritants can help reduce the risk.

9. Does nutrition play a role in the health of the third eyelid?

A balanced diet can support the cat's general health and potentially reduce the risk of eye diseases. Certain nutrients could help reduce inflammatory conditions and strengthen the immune system.

10. Can the third eyelid return to normal without treatment?

In some cases, the third eyelid may recover without treatment, especially if the cause is minor. Nevertheless, it is advisable to consult a veterinarian to ensure that there is no serious underlying condition.