Third Eyelid Problems in Cats: Which Situations Are Normal and Which Are Emergencies?

What is the Third Eyelid (Nictitating Membrane)? Its Physiological Role in Cats

In cats, the third eyelid, medically known as the nictitating membrane , is a thin, translucent structure located inside the eye and normally hidden behind the eyelid margin. This structure serves as a crucial protective mechanism for cats' eye health. This anatomical structure, absent in humans, has played a significant role in cats' evolutionary adaptation to a hunting lifestyle.

One of the third eyelid's primary functions is to rapidly protect the eye's surface. When a cat senses danger or experiences sudden irritation, the nictitating membrane activates within seconds, creating a barrier between the cornea and the outside world. This provides both physical protection against trauma and prevents the eye's surface from drying out uncontrollably. The membrane is also connected to the tear glands and helps moisten the cornea.

The third eyelid is particularly important for tear distribution, mechanical cleansing, and defense against infection . Lymphoid tissues containing immune cells are located within the membrane. These tissues combat microorganisms on the eye surface, reducing the risk of infection. The comprehensive protective role of the third eyelid in cats explains why it is often visible in the early stages of eye diseases.

Under normal circumstances, the third eyelid is either invisible or only partially visible. However, when a cat is sleepy, lethargic, dehydrated, or experiencing trauma, this structure can protrude, covering a significant portion of the eye. While this protrusion is a completely normal reflex in some cases, it can also be the first sign of a serious underlying disease. Therefore, the appearance of the third eyelid is an important clinical clue in assessing eye health.

Appearance of the Third Eyelid in Cats: Situations Considered Normal

The third eyelid can become visible in cats due to completely natural physiological conditions. This appearance does not always indicate illness and often resolves spontaneously within a short time. It is important for owners not to panic but to monitor the situation closely.

One of the most common, normal causes is sleepiness and deep rest . When cats wake up, their third eyelid protrudes for a few seconds, covering part of the eye. This is a completely natural phenomenon associated with the relaxation of the eye muscles. The eyelid usually returns to normal within 10–20 seconds.

Another physiological condition is fatigue and exhaustion . Cats may experience temporary third eyelid ptosis, especially after long play sessions, running, or stressful experiences. This ptosis is usually short-lived and resolves when the cat rests.

Short-term dehydration can also cause the third eyelid to bulge slightly. Temporary disruption of body fluid balance can cause changes in intraocular pressure, causing the membrane to shift forward. This condition usually returns to normal when the cat drinks water and rests.

It's more common for the third eyelid to appear occasionally in kittens. Because the eye muscles are not fully developed, this appearance may occur in short bursts. This condition is usually physiological and disappears once growth is complete.

Finally, environmental factors such as mild irritation, dust intrusion, or wind can also cause the third eyelid to appear momentarily. This condition resolves within a few minutes and, unless there are additional symptoms, usually requires no intervention.

Therefore, not every appearance of the third eyelid is a sign of disease. However, if it recurs frequently, persists for a long time, or is accompanied by other symptoms, an underlying problem should be considered.

Prominence of the Third Eyelid in Cats: Pathological Conditions Requiring Emergency Intervention

Prolonged exposure of the third eyelid, its presence in both eyes, or its protrusion are often signs of a pathological condition . Such conditions often require urgent evaluation, and early intervention can be critical to the cat's quality of life.

One of the most important causes is severe systemic diseases . Gastrointestinal infections, parasitic load, viral illnesses, and severe dehydration can all lead to the prominence of the third eyelid. This condition is often accompanied by weakness, loss of appetite, and general deterioration.

Eye trauma can also cause the third eyelid to bulge. A blow, scratch, foreign object insertion into the cornea, or injuries that affect intraocular pressure cause the membrane to elevate as a protective reflex. Such trauma often requires immediate veterinary attention.

Infections , particularly those affecting the ocular surface such as conjunctivitis and keratitis, can cause the third eyelid to be permanently visible. Symptoms such as eye discharge, redness, sensitivity to light, and occluding the eye are common with the infection.

One pathological cause is Haws Syndrome . In this syndrome, the third eyelid becomes prominent in both eyes. Even if the cat appears generally well, underlying gastrointestinal irritation, parasites, or intestinal imbalance may be present. Haws Syndrome is usually painless, but it is a clinical finding that should not be ignored.

Neurological problems , damage to the periocular nerves, and autonomic nervous system disorders can also cause the third eyelid to droop. This condition can manifest itself, particularly with unilateral prominence, and requires prompt diagnosis.

Many pathological conditions that trigger third eyelid swelling, including eye tumors, intestinal infections, chronic pain, fatigue, and internal diseases, are much easier to treat if detected early. Therefore, if the third eyelid remains visible for more than 24–48 hours , if there are accompanying symptoms, or if it becomes evident in both eyes, the cat should be taken to a veterinarian immediately.

Systemic Diseases That Cause Third Eyelid Elevation

While the appearance of the third eyelid often appears to be due to a local eye problem, it can actually be an early and significant symptom of many systemic diseases . In cats, the third eyelid serves as a "clinical signal" reflecting general poor health, low energy levels, dehydration, and immune system problems. Therefore, when systemic diseases are associated with a prominent third eyelid, the severity of the condition must be assessed.

The main groups of systemic diseases are:

Gastrointestinal diseases: Intestinal infections, parasitic infections (especially severe helminth infestations), and bacterial or viral enteritis affect the cat's overall health and can cause the third eyelid to protrude. This condition is often accompanied by diarrhea, vomiting, loss of appetite, and weight loss. Haws Syndrome is also often associated with intestinal problems.

Severe dehydration: Disruption of fluid balance in the body reduces intraocular pressure, causing the third eyelid to become prominent. This condition can occur due to acute diarrhea, vomiting, fever, or inadequate water intake. Dehydration is a serious metabolic problem that can be life-threatening.

Viral infections: Viral diseases such as feline herpesvirus (FHV), feline calicivirus (FCV), and panleukopenia can lead to prominent eyelid swelling. These infections directly affect eye health because they weaken the overall immune system. Eye discharge, conjunctivitis, fever, and fatigue are common in viral infections.

Pain and systemic inflammation: Pain signals anywhere in the body can affect eye reflexes via the autonomic nervous system, causing the third eyelid to appear. Therefore, the third eyelid can also become prominent in conditions other than the eye.

Parasitic diseases: In cats with a high internal parasite burden, the immune system is suppressed, and the weakened body can cause the third eyelid to remain visible for extended periods. This finding is particularly pronounced in young animals.

In these systemic diseases, the third eyelid is often the "tip of the iceberg." Unless the underlying condition is correctly identified and treated, the third eyelid problem will not be permanently resolved.

The Effects of Eye Infections, Trauma, and Dehydration on the Third Eyelid

Because the third eyelid's function is protective, it reflexively protrudes in the event of any trauma, infection, or irritation to the eye. This protective mechanism aims to protect the ocular surface from further damage. However, its activation generally indicates a pathological process .

Eye infections: Conjunctivitis, keratitis, and corneal ulcers are the most common eye conditions that cause the third eyelid to appear in cats. These infections can be caused by viruses (especially FHV), bacteria, or allergic reactions. Symptoms include eye redness, discharge, watering, sensitivity to light, and squinting. In this case, the third eyelid is raised both to protect against infection and to protect the eye's surface.

Trauma and foreign objects: Cats can sustain blows to their eyes during fights, jumping from heights, or playing. Corneal scratches, foreign object penetration, and severe trauma can cause the third eyelid to suddenly protrude. This condition usually requires immediate intervention, as post-traumatic changes in intraocular pressure can lead to permanent vision loss.

Pain: Pain around the eyes or in the head can also trigger the third eyelid reflex. The source of the pain may not be related to the eye; even conditions such as oral infections, ear problems, and sinusitis can cause the third eyelid to become prominent.

Dehydration: Decreased body fluids reduce eye volume and intraocular pressure, leading to the third eyelid drooping. Therefore, hydration status should be assessed in cats with prominent third eyelids. Dehydration can be life-threatening if not corrected promptly.

The common denominator among these causes is that the third eyelid appears as a "protective alarm." Therefore, each is a clinical condition requiring veterinary evaluation.

Specific Syndromes in Cats That Cause the Third Eyelid to Be Permanently Visible (Haws Syndrome, etc.)

In cats, Haws Syndrome is the first clinical picture that comes to mind when the third eyelid is bilaterally, persistently, and prominently protruding. This syndrome is characterized by the prominence of the third eyelids despite the cat's generally good health. Although rare, it requires careful evaluation.

Haws Syndrome: In this syndrome, the third eyelid is equally prominent in both eyes. Even if the cat is appetite-conscious, energetic, and appears normal, the membrane remains prominent. The underlying cause is usually gastrointestinal irritation, intestinal infections, or a high parasite burden. While the exact cause is unknown in some cases, the syndrome is often temporary, and the third eyelid returns to normal once the underlying intestinal problem is corrected.

Autonomic nervous system disorders: Because the movement of the third eyelid is controlled by the autonomic nervous system, neurotransmission disorders can cause this structure to droop forward. Horner syndrome is an example of this condition. In this syndrome, in addition to the prominence of the third eyelid, pupil constriction and sunken eye are observed.

Chronic pain syndromes: Constant pain signals in the body can cause the third eyelid to reflexively activate. This is particularly common in oral diseases, ear infections, tooth abscesses, and chronic infections in the head and neck region.

Cachhexia and severe emaciation: Prolonged illness, anorexia, and weight loss result in decreased muscle tone around the eye. This can result in the third eyelid remaining permanently visible. This finding often resolves spontaneously as the cat's overall health improves.

While this syndrome and clinical conditions are visible, a definitive diagnosis is made through veterinary examinations, blood tests, and imaging studies. Assessing the duration of the third eyelid problem, whether it is unilateral or bilateral, and any accompanying symptoms are critical to diagnosis.

Diagnosing Third Eyelid Problems: Examination, Tests, and Imaging Methods

A prominent third eyelid in cats can be due to a wide range of causes, from simple eye irritation to systemic disease. Therefore, the diagnostic process must always be multi-stage and comprehensive. It is impossible to reach a definitive conclusion based on a single finding. Veterinarians evaluate both the local condition of the eye and the cat's overall health during the diagnostic phase.

The first step in diagnosis is a clinical examination . The veterinarian assesses the prominence of the third eyelid, whether it is unilateral or bilateral, and any accompanying findings such as eye discharge, redness, or sensitivity to light. This assessment also includes pain, periorbital trauma, and reflex responses. Passive retraction of the eyelid is also an important diagnostic criterion.

Ophthalmological testing is central to the diagnostic process.

• Fluorescein dye test shows if there are scratches, ulcers, or foreign bodies on the cornea.

• The Schirmer tear test detects dry eye syndromes by measuring tear production.

• Intraocular pressure measurement (tonometry) reveals the relationship between diseases such as glaucoma or uveitis and the third eyelid.

If no ocular cause is found, the doctor will often order blood tests . A complete blood count (CBC), biochemistry panel, and electrolyte values provide valuable information about the cat's systemic health. Dehydration, infection, inflammation, and parasitic diseases can be highlighted by these tests.

In some cases, a stool test is necessary to identify gastrointestinal conditions such as Haws Syndrome. High parasite loads, intestinal infections, or imbalances are closely associated with the development of a prominent third eyelid.

Imaging methods such as radiography or ultrasound may also be used when a non-ocular problem is suspected. These methods provide critical information, especially in cases of trauma, tumors, neurological problems, or internal organ disease.

While the diagnostic process involves different stages depending on the severity of the symptoms and the cat's general condition, the primary goal is to accurately determine the underlying cause. Because a third eyelid is only a symptom, treatment should always be focused on the underlying cause.

Treatment of Third Eyelid Problems in Cats: Medical, Supportive, and Surgical Approaches

The goal of third eyelid treatment is always to address the underlying cause . Therefore, the treatment protocol varies depending on whether the problem is caused by a local or systemic eye condition. In some cases, delaying treatment can lead to permanent damage to eye health.

Treatment of Infections: In cases of bacterial conjunctivitis, antibiotic eye drops and ointments are the first-line treatments. For viral infections, antiviral supplements, immune-boosting treatments, and ocular moisturizing preparations are used. In cases of infection, regular treatment and maintaining eye hygiene are crucial.

Treatment for trauma and corneal ulcers: Corneal injuries can cause the third eyelid to suddenly rise. In these cases, antibiotic drops, ulcer-healing medications, and the use of a protective collar to prevent the animal from scratching the eye are necessary. Deep ulcers or damage may require surgery.

Treatment of systemic conditions: If intestinal problems, parasites, or viral infections cause the appearance of the third eyelid, treatment focuses on the gastrointestinal or systemic aspects. Parasite treatments, fluid supplements, antiemetic medications, and appropriate diets are frequently used during this process. In Haws Syndrome, the third eyelid usually disappears on its own once the underlying condition is corrected.

Pain management: Pain in the head and face may cause the third eyelid to protrude. In this case, painkillers and anti-inflammatory medications should be used with caution. Dosage adjustments should be made by a veterinarian.

Treatment of neurological conditions: Treatment for neurological disorders such as Horner Syndrome focuses on reducing the pressure on the nervous system. In such cases, recovery can take several weeks and is generally slow.

Surgical Approaches: Surgery may be necessary in rare cases, such as tumors, severe trauma, or intraocular structural abnormalities. Surgical treatment is only performed if clearly indicated.

Successful treatment depends on accurately identifying the underlying cause and tailoring treatment to the individual patient. Comprehensive and timely treatment usually leads to a full recovery.

Home First Response: What Should Owners Do and Avoid for a Third Eyelid?

Many owners are naturally concerned when a cat's third eyelid becomes visible. However, the right approach can both increase the cat's comfort and prevent potential complications. While home interventions are limited, it's important to take the right steps until you can see a veterinarian.

What to do:

• If your cat squints, rubs, or tries to scratch its eye with its paw, the eye area should be protected from trauma. This is usually a sign of pain or irritation.

• Tap water or irritating liquids should never come into contact with the eye surface. Gentle cleansing with sterile saline may be necessary.

• If the cat is lethargic, has no appetite, or if the third eyelid is prominent in both eyes, consulting a veterinarian should not be delayed.

• The cat's hydration should be ensured and water consumption should be encouraged.

• If there is a discharge from the eye, it can be gently cleaned with a cotton or gauze in one direction.

Things to avoid:

• Human eye drops or medications containing cortisone should never be used. These medications can seriously worsen the condition.

• Home remedies, herbal solutions, or tea compresses recommended on the internet can damage the surface of the eye.

• Trying to open the eyelid manually increases the risk of trauma.

• Keeping the cat in a stressful environment may aggravate the symptoms.

The best approach at home is to safely manage the situation and protect the cat until veterinary evaluation. Because a third eyelid is often a warning sign that something is wrong, a professional examination should not be delayed.

When to See a Veterinarian for a Third Eyelid? Warning Signs and Critical Findings

While the appearance of the third eyelid is normal in some cases, it is often the first and earliest sign of an underlying condition. Therefore, it is crucial for owners to know which symptoms warrant immediate attention.

In the following cases, veterinary evaluation should be performed without delay :

• If the third eyelid has been visible for more than 24–48 hours .

• The eye is noticeably red, swollen or painful.

• If there is yellow, green, or bloody discharge coming from the eye.

• If the cat constantly closes its eyes, squints, or tries to scratch with its paw.

• If the third eyelid has appeared after trauma, a fall, or a fight.

• If the cat has the following symptoms: vomiting, diarrhea, weakness, fever, loss of appetite, weight loss.

• If the third eyelid is prominent in both eyes .

• If vision loss, light sensitivity or pupillary imbalance is observed.

• If dehydration, collapse or serious illness is suspected.

Cats tend to hide their pain and discomfort. Therefore, by the time physical signs appear, the disease is usually advanced. The third eyelid acts as an "early warning system" in this regard. Delay both prolongs treatment and increases the risk of complications.

Early intervention ensures rapid recovery and prevents complications in most cases, so it's crucial for owners to take third eyelid changes seriously.

Frequently Asked Questions (FAQ)

What is the third eyelid in cats and is it normally expected to be visible?

The third eyelid is a thin structure called the nictitating membrane that protects a cat's eye. It is normally hidden just behind the eyelid margin and is invisible. It may appear only momentarily when the cat is sleeping deeply, is tired, or during short-term physiological states. However, prolonged or prominent nictitating ...

My cat's third eyelid suddenly appeared. Is this always an emergency?

It's not always an emergency, but it should be taken seriously. If the third eyelid returns to normal within a few minutes or hours, this may be due to fatigue, drowsiness, or temporary irritation. However, if the third eyelid remains visible for more than 24–48 hours or if other accompanying symptoms are present, a veterinary visit is warranted.

What diseases most often cause the appearance of the third eyelid in cats?

Gastrointestinal infections, parasites, viral infections (FHV, FCV), eye infections, uveitis, trauma, neurological problems, dehydration, and Haws Syndrome are among the most common causes. Furthermore, due to weakened immune systems in systemic diseases, the third eyelid may become prominent.

What does it mean if my cat's third eyelid is visible in both eyes?

Bilateral bleariness generally suggests a systemic disease or specific syndromes such as Haws Syndrome. This condition may be due to gastrointestinal problems, parasite burden, or intestinal infections. Even if the cat appears generally well, this finding alone warrants a veterinary examination.

What could be the reason if the third eyelid appears only in one eye?

Unilateral appearance is often due to local causes. Ocular trauma, foreign bodies, corneal scratches, nerve damage (e.g., Horner's syndrome), eye infections, or pain are the most common causes. A unilateral prominent third eyelid often requires more urgent evaluation.

What exactly is Haws Syndrome in cats? Is it dangerous?

Haws Syndrome is a condition characterized by bilateral prominence of the third eyelids in cats. It is usually associated with gastrointestinal irritation, infection, or parasites. In most cases, the cat appears generally healthy. This syndrome is usually temporary, and the third eyelid returns to normal once the underlying problem is resolved. However, veterinary care is still essential.

If my cat's third eyelid is visible, is there a risk of vision loss?

The appearance of the third eyelid does not directly cause vision loss. However, if the underlying condition is caused by a corneal ulcer, severe infection, trauma, or intraocular pressure disturbances, permanent vision loss can occur if treatment is delayed. Therefore, early diagnosis is extremely important.

How do eye infections cause the third eyelid to appear?

Infections such as conjunctivitis and keratitis cause inflammation on the surface of the eye. This inflammation causes the third eyelid to protrude as a protective reflex. Redness, discharge, light sensitivity, and eye closing behaviors often accompany this condition.

What can I do at home when my cat's third eyelid becomes prominent?

Gentle cleaning with a sterile serum can be performed, the cat can be placed in a stress-free environment, and water intake can be increased. However, any eye drops, cortisone medications, or human eye products should never be used. Home interventions are limited, and a veterinary examination should not be delayed.

My cat has a loss of appetite when her third eyelid is visible. Could this be related?

Yes. Anorexia is a significant symptom of systemic diseases and is frequently associated with the appearance of the third eyelid. Gastrointestinal upset, viral infections, and pain can cause both anorexia and the appearance of the third eyelid. This combination makes the situation urgent.

Why does dehydration affect the third eyelid?

Dehydration reduces intraocular pressure, reducing the eye's normal anatomical support. When the eye's volume decreases, the third eyelid becomes prominent, drooping forward. This is an indication that the cat's fluid balance is severely compromised.

Can stress cause a third eyelid to appear in cats?

Yes. Stress can affect eye reflexes through the autonomic nervous system. The third eyelid may appear temporarily, especially during periods of sudden environmental changes, household stress, moving, or the addition of a new pet. However, if this symptom persists, an underlying condition should be ruled out.

If my cat's third eyelid is visible, will it heal on its own?

In some physiological causes (fatigue, drowsiness, short-term irritation), it may resolve spontaneously. However, for pathological causes, resolution depends on treating the underlying problem. Generally, if it persists for a long time, it is unlikely to disappear on its own and veterinary intervention is essential.

Could the appearance of a third eyelid be a sign of pain?

Yes. Unilateral prominence, in particular, often indicates pain. Eye injuries, foreign bodies, corneal ulcers, or facial infections can cause a pain-related third eyelid reaction.

If my cat's third eyelid is visible, could this be a sign of neurological disease?

The third eyelid may become prominent in autonomic nervous system disorders such as Horner Syndrome. This condition often also presents with pupil constriction, sunken eyes, and drooping eyelids. Neurological signs should be evaluated by a veterinarian.

Is it normal if the third eyelid is only visible when waking up?

Yes. When cats wake from deep sleep, their third eyelid may protrude for a few seconds. This is completely normal and physiological. The problem is that the third eyelid remains visible for a long time.

My cat's third eyelid suddenly appears and then disappears. What does this fluctuation mean?

This condition can often be due to gastrointestinal issues, mild dehydration, or stress factors. If fluctuations become more frequent or reoccur throughout the day, an underlying health issue is likely and a veterinary evaluation is necessary.

My cat doesn't want to play when her third eyelid is visible. Is this a sign of illness?

Yes. Low energy , loss of appetite , and decreased desire to play, combined with a prominent third eyelid, are strong indicators of a systemic disorder. Such behavioral changes should not be ignored.

Are there any long-term complications in cats with third eyelid problems?

If the problem is caused by trauma or infection and treatment is delayed, corneal damage, chronic pain, and vision problems can develop. If systemic conditions are left untreated, the third eyelid problem can persist for a long time and significantly reduce the cat's quality of life.

Could the appearance of a third eyelid be an age-related condition in cats?

In older cats, the third eyelid may become more prominent due to decreased muscle tone, increased tendency for dehydration, and increased prevalence of chronic diseases. However, this is still not considered normal and should be evaluated.

Sources

• American Association of Feline Practitioners (AAFP)

• Merck Veterinary Manual

• Feline Ophthalmology Clinical Guidelines

• Cornell Feline Health Center

• Mersin Vetlife Veterinary Clinic – Open on Map: https://share.google/jgNW7TpQVLQ3NeUf2