Cat Third Eyelid Showing Why

As a cat owner, you may occasionally notice a pale, whitish film creeping across your cat’s eye from the inner corner. That is the third eyelid (nictitating membrane), a protective structure normally hidden when your cat is awake and alert. When it remains visible or partially covers the eye, it often signals an underlying issue. Understanding why this happens helps you decide whether to monitor at home or seek veterinary attention.

Quick Q&A: Common Questions

Question: Why is my cat’s third eyelid showing?

Answer: A visible third eyelid can be due to a benign condition called Haw’s syndrome (often linked to intestinal worms or gut upset), eye irritation or injury, dehydration, pain, or neurological problems. In many cases it is temporary and resolves once the underlying cause is treated. However, if accompanied by other symptoms like squinting, discharge, or lethargy, prompt veterinary evaluation is recommended.

Understanding the Third Eyelid

The third eyelid is a thin, T‑shaped piece of tissue located in the inner corner of each eye. It contains a gland that produces a portion of the tear film and helps distribute moisture across the eye. In healthy cats, the third eyelid remains retracted out of sight, held in place by the eye’s position and the surrounding muscles. When it becomes prominent, it usually means something is pulling the eye inward (as with dehydration or weight loss), or that the eye itself is painful, causing the eyelid to protrude protectively.

Common Causes of a Visible Third Eyelid

Haw’s Syndrome

Haw’s syndrome is a common, benign condition in which both third eyelids protrude simultaneously, often without any other eye symptoms. It is frequently associated with gastrointestinal upset, such as diarrhea or vomiting, and sometimes with intestinal parasites (especially tapeworms). The exact mechanism is unclear, but the condition typically resolves on its own within a few weeks once the gut issue is treated.

Eye Irritation or Injury

Any local irritation to the eye can trigger the third eyelid to move forward. Examples include corneal scratches, foreign bodies like grass seeds, conjunctivitis (pink eye), or feline herpesvirus. If only one eye is affected, an ocular problem is more likely than a systemic condition. Squinting, redness, discharge, or pawing at the eye often accompany these cases.

Systemic Illness or Dehydration

Systemic problems can cause the third eyelid to show in both eyes. Dehydration reduces the volume of fluid behind the eye, allowing the globe to sink slightly backward and the eyelid to move forward. Fever, severe pain from conditions like pancreatitis, or significant weight loss can also make the third eyelid more visible. Cats that are lethargic or have gastrointestinal symptoms may show this sign.

Neurological Issues

Less commonly, a prominent third eyelid may indicate a neurological problem, especially if the pupils are different sizes (anisocoria), the cat is dizzy tilting its head, or the eyelid protrusion is one‑sided. Conditions such as Horner’s syndrome (damage to the sympathetic nerves supplying the eye) can cause a drooping eyelid, constricted pupil, and visible third eyelid on the same side. Head trauma, ear infections, or tumors can also be responsible.

When to Seek Veterinary Care

A single, brief episode with a known trigger (like a recent stomach upset) may not be alarming, but you should contact your veterinarian if:

• The third eyelid stays up for more than a few hours.
• Only one eye is affected.
• Your cat is squinting, crying, pawing at the eye, or has discharge.
• There are other systemic signs: vomiting, diarrhea, fever, loss of appetite, lethargy.
• The pupils appear unequal or the cat seems off balance.

Even if both eyes are equally affected and your cat otherwise seems well, it is wise to schedule an appointment to rule out underlying parasites or illness.

What to Expect at the Vet Visit

Physical Examination

Your veterinarian will start with a general physical exam, checking your cat’s temperature, hydration status, body condition, and abdominal tenderness. They will also perform a thorough eye examination using an ophthalmoscope to look at the cornea, pupil, and lens. The vet may gently evert the eyelids to check for foreign bodies.

Diagnostic Tests

Depending on findings, tests may include:

• Schirmer tear test to measure tear production.
• Fluorescein stain to detect corneal ulcers or scratches.
• Bloodwork to assess hydration, organ function, and signs of infection.
• Fecal exam to check for intestinal parasites if Haw’s syndrome is suspected.
• Neurological exam if nerve damage is possible.

Home Care and Monitoring

If your vet diagnoses a benign condition like Haw’s syndrome and your cat is otherwise healthy, simple home care may be enough:

• Ensure fresh water is always available to prevent dehydration.
• Feed a balanced diet; address any gastrointestinal upset with veterinary guidance.
• Keep the eyes clean by gently wiping away any discharge with a damp, soft cloth.
• Monitor for changes: note if the eyelid retracts on its own, if the cat stops eating, or if symptoms worsen.

Never use over‑the‑counter eye drops without a vet’s approval, as some can irritate or damage the eye.

Prevention

While not all causes are preventable, you can reduce risks:

• Keep up with routine deworming and fecal checks as recommended by your vet.
• Provide a stress‑free environment to minimize flare‑ups of feline herpesvirus.
• Protect your cat from eye injuries by keeping sharp objects away and trimming claws.
• Maintain good hydration and nutrition, especially for older or sick cats.
• Have regular wellness exams to catch systemic issues early.

Seeing your cat’s third eyelid can be startling, but in many cases it is a temporary, treatable sign. By staying observant and seeking timely veterinary care, you can help your feline companion return to normal quickly and comfortably.