Why Is My Cat’s Third Eyelid Showing?

A cat's third eyelid, known as the nictitating membrane, is usually hidden and not visible. However, when it protrudes, it can signal illness or injury.

Discover the significance of a cat's third eyelid and what it means if it becomes visible.

What Does a Cat’s Third Eyelid Do?

The nictitating membrane is located at the inner corner of each eye. It is usually retracted, making it invisible. However, certain conditions may cause it to protrude and partially cover the eye.

How to Spot a Cat's Third Eyelid

Seeing your cat's third eyelid is uncommon. A healthy third eyelid appears as a crescent-shaped slit in the eye's corner.

Reasons for a Cat's Third Eyelid to Appear

Often, the appearance of the third eyelid indicates a problem.

Various factors can cause a cat's third eyelid to protrude. Some are normal, while others indicate issues.

Sleepiness or Relaxed State

It's normal for the third eyelid to show when a cat is relaxed or tired. You may notice that the third eyelids are up while your cat sleeps or right after waking. The third eyelid should retract as soon as the cat is awake and alert. If the third eyelid stays up for longer than

Sedation or Anesthesia

If your cat was given anesthesia or sedation for a medical procedure, the third eyelid will appear and partially cover the eye due to extreme physical relaxation. The effect may last for several hours after waking but should gradually go away. This is considered normal and is not a problem unless the third eyelid remains up after the day of the procedure.

Conjunctivitis

The conjunctiva is a thin, transparent mucous membrane that lines the inside of the eyelids and covers the front part of the eye. Sometimes called "pink eye," conjunctivitis simply means inflammation of the conjunctiva. It may be caused by an infection, allergies, injury, or an eye irritant. It is not uncommon for conjunctivitis to cause inflammation and protrusion of the third eyelid. Cats with conjunctivitis will typically be treated with medicated eye drops or ointment that contain antibiotics and/or steroids.

Corneal Ulcers

The cornea is a clear layer covering the front of the eye. A corneal ulcer, a wound to this layer, causes pain and inflammation, potentially causing the third eyelid to show. These ulcers are often due to eye injuries or irritants. Corneal ulcers can quickly worsen, needing veterinary treatment. Cats may require eye and oral medications for healing.

Uveitis

The uvea is the eye's middle layer, rich in blood vessels. Inflammation of this area is called uveitis, often causing redness and pain. The third eyelid might also be affected.

Glaucoma

Glaucoma is a painful condition where pressure builds up in the eye due to improper drainage of aqueous humor (fluid within the eye). This pressure damages the optic nerve, potentially leading to blindness. Third eyelid inflammation may sometimes accompany glaucoma.

Cherry Eye

The third eyelid contains a gland that can become swollen and look like a round protrusion from the inner corner of the eye. This is called prolapse of the nictitating membrane, or cherry eye. It is relatively uncommon in most cats but common in Burmese cats. Surgery is the treatment for cherry eye.

Eye Growths

Growths, tumors, masses, or cysts near the eye may cause the third eyelid to protrude. If you notice an unusual growth or swelling in your cat's eye, contact your vet promptly to prevent complications.

Horner’s Syndrome

Horner's syndrome is a neurological disorder caused by nerve dysfunction, affecting the eyes and facial muscles, leading to asymmetry. The third eyelid often becomes prominent in one eye, and the eyelids droop with the eye appearing "sunken in." Causes include trauma or tumors, but the specific cause is sometimes unknown. The condition may resolve independently.

When to Seek Medical Attention

If your cat's eyelid protrudes and isn't due to sleep, relaxation, sedation, or anesthesia, it likely indicates a problem. Contact your veterinarian promptly for advice. If other signs of illness are present, ensure your cat receives a veterinary checkup. Never apply anything to the eye without veterinary guidance, as this can worsen the situation. Eye issues can rapidly escalate, so immediate veterinary attention is essential.