THIRD EYELID SHOWING (NICTITATING MEMBRANE) IN DOGS/CATS
WHAT THIS SYMPTOM USUALLY MEANS
The third eyelid (the inner corner membrane) becomes visible when the eye is painful, dehydrated, irritated, infected, or when systemic illness is present. In cats, a protruding third eyelid can indicate Horner’s syndrome, dehydration, GI illness, or severe eye disease. In dogs, it often reflects pain, neurologic issues, or “cherry eye” if the gland prolapses.
Seeing the third eyelid is never normal unless a pet is deeply relaxed or just waking up
MOST COMMON CAUSES
MILD OR SELF-LIMITING CAUSES (COMMON)
• Mild dehydration
• Temporary irritation or dust
• Fatigue or waking from sleep
• GI upset in cats causing transient protrusion
• Mild pain or discomfort
MEDICAL CAUSES THAT NEED DIAGNOSIS (MODERATE CONCERN)
• Conjunctivitis
• Corneal irritation or ulcer
• Horner’s syndrome (cats and dogs)
• Cherry eye (gland prolapse)
• Eyelid inflammation or trauma
• Viral infections in cats (FHV)
• Systemic illness (especially GI disease in cats)
EMERGENCY CAUSES (HIGH CONCERN)
• Third eyelid raised due to major eye pain
• Severe corneal ulcer
• Glaucoma
• Neurologic disease
• Trauma to the eye or head
• Third eyelid + sudden blindness
RED FLAGS: WHEN THIS IS AN EMERGENCY
• Third eyelid visible + squinting or rubbing
• Third eyelid + cloudy or blue eye
• Third eyelid + unequal pupils
• Third eyelid + lethargy, fever, or vomiting
• Third eyelid suddenly protruding after trauma
If you’re unsure, treat it as urgent.
AT-HOME CARE YOU CAN START NOW
• Use a cone to prevent rubbing.
• Keep your pet calm and indoors.
• Flush gently with sterile saline if dust or debris suspected.
• Do not use medicated or leftover eye drops—they can worsen ulcers.
These steps do not replace a veterinary exam if symptoms continue or worsen.
WHAT A VETERINARIAN WILL CHECK
• Full eye exam (cornea, conjunctiva, eyelids)
• Fluorescein stain to check for ulcers
• Eye pressure test for glaucoma
• Neurologic exam for Horner’s syndrome
• Tear production test
• Exam for cherry eye or gland prolapse
• Systemic evaluation in cats with GI-linked third eyelid elevation
MOST LIKELY DIAGNOSES (BASED ON 40 YEARS OF CASES)
• Corneal ulcer
• Conjunctivitis
• Cherry eye
• Horner’s syndrome
• Viral infection (cats)
• Systemic illness (cats, GI disease)
• Eyelid trauma or foreign object
BREEDS OR AGES AT HIGHER RISK
• Brachycephalics — cherry eye and irritation
• Spaniels — dry eye and gland prolapse
• Cats (all breeds) — GI illness-related third eyelid elevation
• Older pets — neurologic or systemic disease
WHEN YOU SHOULD SCHEDULE A VETERINARY VISIT
- Today: painful, red, cloudy, or swollen eye
- 48 hours: persistent third eyelid without pain
- 1 week: mild, intermittent third eyelid elevation
- Monitor: third eyelid after a nap only
EXPECTED RECOVERY TIME
• Minor irritation: 1–3 days
• Conjunctivitis: 1–2 weeks
• Cherry eye: requires surgery
• Horner’s syndrome: 2–8 weeks, sometimes longer
• Ulcers: 1–3 weeks
• GI-illness related (cats): resolves with treatment of primary issue
HOW THIS SYMPTOM RELATES TO LONGEVITY
A visible third eyelid can indicate chronic inflammation, systemic disease, discomfort, or early neurologic change. Addressing these early supports long-term comfort, mobility, and neurological health
WHEN TO CONSIDER A LONGEVITY CONSULT
For recurrent eye issues, chronic systemic disease, or neurologic signs. Longevity planning ensures stability and early detection of health decline.
FOR CANCER-RELATED CONCERNS
Masses behind the eye can elevate the third eyelid. If symptoms are persistent or asymmetric, visit Pet Cancer Navigator for guidance.
FAQ
Why is only one third eyelid showing?
Often due to unilateral pain, Horner’s syndrome, or local irritation.
Can dehydration cause the third eyelid to rise?
Yes—especially in cats.
Is third eyelid elevation painful?
Often, but not always. Pain must be assumed until proven otherwise