Cat Third Eyelid Showing Sometimes

Many cat owners have glimpsed a thin, whitish or pinkish membrane sliding across their cat’s eye, either partially or fully. This is the nictitating membrane, commonly called the third eyelid. While a brief appearance after waking or during deep relaxation can be normal, a third eyelid that shows repeatedly or stays visible for longer periods often signals an underlying issue. Understanding why this happens and when to act is key to keeping your feline friend healthy.

Quick Q&A: Common Questions

Question: Why does my cat’s third eyelid keep showing sometimes?

Answer: The most common reason for intermittent third eyelid protrusion is a condition called Haw syndrome, often linked to intestinal parasites or mild gastrointestinal upset. Other causes include dehydration, pain, neurological disorders such as Horner’s syndrome, or local eye irritation. A veterinary examination is recommended to pinpoint the cause and rule out more serious conditions.

What Is the Third Eyelid? A Quick Overview

The third eyelid is a protective membrane located in the inner corner of a cat’s eye. It contains a T-shaped cartilage and a gland that produces about 30% of the cat’s tear film. In a healthy, alert cat, the third eyelid is tucked out of sight. It appears only momentarily during blinking or when the cat is very sleepy. When the membrane remains visible for extended periods or reappears frequently, it suggests something is interfering with normal eye function or the sympathetic nervous system’s control of the eye.

Common Causes of Intermittent Third Eyelid Showing

1. Haw Syndrome (Feline Haw)

This syndrome is named after the third eyelid’s anatomic term (haw) and is characterized by bilateral, symmetrical protrusion of the third eyelids without any other eye problems. It often appears suddenly in young to middle-aged cats and is frequently associated with:

• Intestinal parasites (e.g., tapeworms, roundworms)
• Gastrointestinal upset (vomiting, diarrhea)
• Stress or underlying systemic illness

Haw syndrome typically resolves on its own within a few weeks once the underlying trigger is treated. However, it is important to have a veterinarian rule out other causes.

2. Horner’s Syndrome

This neurological disorder results from damage to the sympathetic nerve supply to the eye and surrounding muscles. Signs include:

• Third eyelid protrusion on one side only
• Drooping of the upper eyelid (ptosis)
• A constricted pupil (miosis)
• Sunken appearance of the eye

Causes range from ear infections and neck trauma to tumors affecting the nerve pathway. A thorough neurological exam is needed.

3. Dehydration or Systemic Illness

When a cat becomes dehydrated or suffers from a fever, infection, or metabolic disease, the third eyelid may protrude due to loss of supportive fat behind the eye or general weakness. Conditions such as kidney disease, hyperthyroidism, or anemia can lead to intermittent showing.

4. Eye Surface Problems

Local irritation can cause the third eyelid to lift or stay up as a protective response. Possible triggers include:

• Corneal ulcers or scratches
• Conjunctivitis (pink eye)
• Foreign bodies (grass awns, dust)
• Uveitis (inflammation inside the eye)

These conditions often come with squinting, excessive tearing, or redness, helping to distinguish them from neurological causes.

5. Pain Anywhere in the Body

Cats in pain (from dental disease, arthritis, abdominal discomfort, etc.) may retract their eyeballs slightly, causing the third eyelid to become more prominent. This is sometimes called the “Haw sign” and can be a subtle indicator that your cat is hurting.

When to Observe at Home vs. When to See the Vet

Observe at home if:

• The third eyelid appears only when your cat is very relaxed or waking up and retracts fully within seconds.
• Both eyes are equally affected, and your cat is otherwise eating, drinking, playing, and eliminating normally.
• You have recently dewormed your cat or treated for parasites as recommended by your vet.

See the vet if:

• The third eyelid remains visible for more than a few hours at a time.
• Only one eye is affected (suggests local or neurological problem).
• Your cat shows other symptoms: squinting, pawing at the eye, discharge, lethargy, vomiting, diarrhea, appetite changes, or head tilt.
• The third eyelid looks swollen, red, or has a mass.

What to Expect at the Veterinary Visit

Your veterinarian will perform a complete physical and ophthalmic examination. Tests may include:

• Schirmer tear test to measure tear production
• Fluorescein stain to check for corneal ulcers
• Tonometry to measure intraocular pressure if glaucoma is suspected
• Bloodwork and urinalysis to evaluate for systemic diseases (kidney, liver, thyroid)
• Fecal examination for parasites if Haw syndrome is suspected
• Neurologic assessment if Horner’s syndrome is possible

Treatment depends on the underlying cause. For parasite-related Haw syndrome, deworming medication is given. Corneal ulcers may require antibiotic eye drops. Horner’s syndrome often resolves if the inciting injury heals; rarely, it requires specialized care.

Prevention and Ongoing Care

You cannot prevent every cause of third eyelid protrusion, but you can reduce risks:

• Maintain routine deworming and fecal checks as recommended by your vet.
• Provide a balanced diet and fresh water to prevent dehydration.
• Keep your cat indoors or supervised to reduce trauma and fight injuries.
• Schedule annual wellness exams so underlying conditions are caught early.
• Reduce stress with a stable environment, enrichment, and multiple resources if you have multiple cats.

If your cat’s third eyelid appears off and on without other signs, keep a log of when it happens and bring it to your veterinarian’s attention. Intermittent showing is often a clue that your cat’s body is out of balance, and with proper diagnosis, most causes are treatable. Your cat relies on you to notice these subtle signals. A timely veterinary visit ensures your feline companion remains comfortable, pain-free, and seeing clearly.