TL;DR: A visible third eyelid often indicates irritation or Cherry Eye and should be evaluated by a vet within 24 hours if signs of pain or discharge occur. Taking clear photos helps your veterinarian assess urgency and monitor progress during triage.
What is the third eyelid and why is it visible in my dog?
It can be quite concerning to see a pink or white membrane covering part of your dog's eye. This is the nictitating membrane, or 'third eyelid.' While it usually stays tucked away, it can become visible or swollen due to irritation, injury, or underlying health issues like 'Cherry Eye,' which occurs when the gland of the third eyelid prolapses and becomes inflamed.
Is a visible or swollen third eyelid a veterinary emergency?
The urgency level for a visible or swollen third eyelid is generally Medium. While often not an immediate life-threatening crisis, eye conditions can progress rapidly and cause significant discomfort. You should schedule a veterinary appointment within 24 hours to prevent permanent damage or secondary infection if your dog shows the following symptoms:
- Pawing at the eye
- Squinting excessively
- Thick yellow or green discharge
How can taking a photo of my dog's eye help the veterinarian?
Taking a clear, well-lit photo of your dog's eye can be incredibly helpful for remote triage. Providing a photo allows a veterinary professional to:
- Assess the exact position of the membrane
- Evaluate the level of redness and severity of swelling
- Determine how quickly your pet needs to be seen
- Establish a baseline for monitoring if the condition worsens while you wait for your appointment
Clinical Context (Merck Veterinary Manual)
In dogs, unilateral prolapse of the nictitating membrane, along with eyelid swelling, can be a sign of orbital cellulitis. Other signs of orbital cellulitis include acute pain on opening the mouth, forward displacement of the globe, and conjunctivitis. Keratitis may develop secondary to lagophthalmos. While predominantly seen in large and hunting breeds, foreign bodies (e.g., migrating grass awns) and zygomatic sialadenitis are additional causes. Orbital hemorrhage and neoplasia may mimic inflammation, but usually without pain on opening the mouth. In young dogs and certain breeds, hypertrophy, inflammation, and prolapse of the gland of the nictitating membrane (cherry eye) is common, resulting in a swollen, protruding red glandular mass and mucopurulent discharge.
Chapter: Ophthalmology
Source: The Merck Veterinary Manual, 11th Edition (Page 490)