Dog Third Eyelid Showing: Causes, Cherry Eye & Vet Advice | New Zealand Guide

If your dog's third eyelid is showing, the thin pale membrane in the inner corner of the eye has become visible when it normally stays hidden. A brief flash in a relaxed or sleepy dog is usually harmless. A third eyelid that stays raised, though, often signals a problem with the eye itself or with the nerves that control it — and some of those causes need a veterinarian the same day. This guide explains what the nictitating membrane does, why it becomes visible (including cherry eye and Horner's syndrome), how to tell one-eye causes from both-eyes causes, what your vet will check, and what safe home care looks like once the eye has been cleared.

Quick answer: An occasional third-eyelid flash in a drowsy dog is normal. A third eyelid that stays up — especially with squinting, redness, discharge, a sunken or bulging eye, or a red mass in the corner — warrants a veterinary exam. Sudden changes in one eye, or both third eyelids up in a dog that seems sick, should be seen promptly.

What is a dog's third eyelid (nictitating membrane)?

The third eyelid, known medically as the nictitating membrane, sits in the inner corner of each eye — the medial canthus, nearest the nose — and sweeps across the surface like a windshield wiper when the eyeball retracts. You rarely see it unless your dog is drowsy, yet it works constantly to protect and lubricate the cornea (Merck Veterinary Manual).

It produces a large share of your dog's tears

At its base sits a tear gland that produces a significant share of the eye's watery (aqueous) tears — commonly cited as roughly a third. That fact matters later: it is why veterinary ophthalmologists reposition a prolapsed gland rather than remove it.

Why is my dog's third eyelid showing?

A third eyelid becomes visible for two broad reasons: the membrane itself changes — it swells, or its gland slips out of place — or the eyeball shifts backward or shrinks, so the membrane passively rises to cover the gap. These are the causes veterinarians see most.

Cherry eye (a prolapsed third-eyelid gland)

"Cherry eye" is the everyday name for a prolapsed nictitating membrane gland: the tear gland slips out of position and bulges as a smooth red or pink mass in the inner corner. It is the most common third-eyelid disorder in dogs and usually appears in young animals. In a UK primary-care study of more than 905,000 dogs, the one-year prevalence was about 0.2% and the median age at diagnosis was under eight months (O'Neill et al., 2022). Some breeds are far more prone than others: that study found sharply higher odds in the Neapolitan Mastiff, English Bulldog, Cane Corso, Lhasa Apso and American Cocker Spaniel, among others. Cherry eye is rarely an emergency, but it should be examined and repaired — see below on why the gland is repositioned, not removed.

A painful eye pulling back into the socket

When an eye hurts, a dog retracts the eyeball slightly into the socket and the third eyelid rises to shield it. Common triggers include a scratch, a foreign body such as a grass seed, or a corneal ulcer. If your dog is also squinting or holding one eye shut, tearing, or shying from light, treat it as painful and time-sensitive — this pattern is usually in one eye and quick to appear.

Horner's syndrome and other nerve problems

Horner's syndrome is a disruption of the sympathetic nerve supply to the eye. It produces a classic cluster of signs on the affected side: a raised third eyelid, a smaller pupil, a slightly droopy upper lid, and a sunken-looking eye (Zwueste & Grahn, 2019). It is often idiopathic — no cause is ever found, and many dogs recover over weeks to months — but it can also follow middle-ear disease, trauma, or problems along the neck and chest, so it deserves a proper work-up rather than watching and waiting at home.

A sunken, small or shrinking eye

Anything that makes the eye sit deeper or look smaller lets the third eyelid rise passively: dehydration, rapid weight loss, loss of the fat pad behind the eye in older dogs, wasting of the chewing muscles, or a naturally small or shrunken eyeball. Here the third eyelid is a messenger for a wider health issue, not an eye disease of its own.

Both third eyelids up when a dog is sick — and the "Haw syndrome" question

When both membranes are raised together, look at the whole dog. Bilateral protrusion in dogs most often accompanies dehydration, weight loss, sedation, or general illness — which is why owners often notice a dog's third eyelid up when it is sick. You may see the term "Haw syndrome" used for two raised third eyelids in a young, otherwise healthy pet; strictly speaking, that self-resolving condition is described in cats, often alongside digestive upset, and is not well documented in dogs. In a dog, two raised third eyelids plus lethargy, vomiting, stiffness, or refusal to eat means see a vet — rarely, a rigid dog with both membranes up can even signal tetanus.

One eye or both eyes? A quick way to read the situation

Cherry eye: why the gland is repositioned, not removed

Because cherry eye is so common — and the old "just snip it off" shortcut still circulates — this point is worth making plainly. The prolapsed lump is a working tear gland. Removing it can leave the eye chronically short of tears: a controlled study in dogs showed that excising the third-eyelid gland reduced tear production and disturbed the ocular surface (Saito et al., 2001), raising the lifelong risk of keratoconjunctivitis sicca (dry eye). The standard of care is surgical repositioning that tucks the gland back into place (Cornell Riney Canine Health Centre). If removal is ever suggested, ask about repositioning first, or request a referral to a veterinary ophthalmologist.

Red flags: when a showing third eyelid needs a vet now

• The eye looks painful — squinting, held shut, pawing at it, or shying from light
• Redness, cloudiness, or colored discharge (yellow or green)
• A red or pink mass bulging from the inner corner
• The eye looks sunken, bulging, or a different size than the other
• Both third eyelids are up and your dog seems unwell, off food, stiff, or lethargic
• Sudden onset, or any change after a knock, fall or scuffle

If you notice any of these, book a same-day appointment. Eyes can deteriorate quickly, and problems such as ulcers or glaucoma are far easier to treat early. For a broader overview, see the warning signs of a dog eye infection and our complete guide to dog eye health.

Common mistakes to avoid

• Pushing the membrane or a cherry-eye mass back with a finger. You can bruise the gland and introduce infection.
• Using human eye drops. Redness-relief and steroid drops formulated for people can seriously worsen a scratched or ulcerated canine cornea.
• Waiting "a few more days" on a painful eye. An ulcer can deepen fast; squinting plus a raised third eyelid is a same-day problem.
• Letting the dog rub. Until the vet visit, prevent pawing and rubbing — a cone from a previous procedure is useful here.

What your veterinarian will check

A third-eyelid exam is quick and painless. Your vet compares pupil size on each side, checks for pain, and usually runs two simple tests: a fluorescein stain to catch a corneal scratch or ulcer, and a Schirmer tear test to measure tear production. They also inspect the membrane itself for a prolapsed gland or scrolled cartilage, and, when Horner's syndrome is suspected, examine the ears and the neurologic pathway down the neck and chest.

What to note or photograph before the appointment

• A clear photo of the eye in good light, plus one of the normal eye for comparison
• When it started, whether it comes and goes, and whether one or both eyes are involved
• Any squinting, discharge, appetite change, vomiting, stiffness or recent trauma
• Any products already applied to the eye — bring the bottle

Safe home care once the eye is healthy

Home care does not fix cherry eye, Horner's syndrome or a corneal injury — those need veterinary treatment, and nothing below should delay that appointment. What you can safely do, once a veterinarian has confirmed the eye is healthy and comfortable, is keep the inner corner clean day to day, which matters most in breeds prone to tearing and staining. Gently wipe away crust with a clean, damp pad, and flush visible dust or pollen with a sterile, isotonic eye rinse made for dogs. For a step-by-step routine, see how to safely clean your dog's eyes at home.

Formulation matters when you choose a rinse. Our non-medicated dog eye drops are built to ophthalmic standards: sterile, filtered to 10 microns and buffered to pH 7.0–7.2, close to a dog's natural tear film, so they flush without stinging. They carry sodium hyaluronate at 0.05% — the water-binding molecule found in natural tears — plus pro-vitamin B5, aloe vera at 8% and chamomile at 2%, and leave out the bleach, alcohol and fragrance that harsher "tear-stain" liquids rely on. They are a daily-hygiene product only, never appropriate on a painful, red or raised-membrane eye. For everyday nutritional support of normal eye comfort in healthy dogs, some owners also add Advanced Vision for Dogs, a plant-based liquid antioxidant blend (berry extracts, turmeric, ginger) dosed by body weight — it is a supplement, not a medicine, and it does not treat, cure or prevent any eye condition, including a visible third eyelid. You can browse the rest of our eye drops for dogs and the wider dog ear and eye care collection, and flat-faced breeds may find our brachycephalic breed care guide useful — but none of this replaces a veterinary exam when the third eyelid stays up.

Frequently asked questions

Is a dog's third eyelid showing an emergency?

Not always. A brief flash in a relaxed or sleeping dog is normal. It becomes urgent when the eye looks painful, red, cloudy, sunken or bulging, when there is colored discharge or a red mass in the corner, or when both membranes are up and your dog seems unwell.

Why is my dog's third eyelid showing in one eye only?

One-sided causes include a painful cornea (scratch, ulcer, foreign body), cherry eye, and Horner's syndrome. A single raised third eyelid with squinting or tearing suggests pain and should be examined the same day.

Why is my dog's third eyelid up when he is sick?

Illness, dehydration and weight loss can make the eyeball sit deeper in the socket, letting both third eyelids rise passively. The membranes usually settle as your dog recovers, but a sick dog with both third eyelids up should be seen by a vet.

Will cherry eye go away on its own?

It rarely resolves for good. The gland may slip back briefly, but it usually needs surgical repositioning. Leaving it exposed risks drying and inflammation, so have it examined even if it looks better on some days.

Can I push my dog's cherry eye back in myself?

No. Home manipulation can injure the delicate gland and introduce infection. Keep the area clean, stop your dog rubbing it, and let a vet reposition it properly.

My dog's third eyelid shows only when sleepy — is that normal?

Usually yes. Many dogs reveal the membrane as they drift off or fully relax, and it retracts as soon as they perk up. If it stays visible while your dog is alert and active, have it checked.

Scientific References

1. O'Neill DG, Yin Y, Tetas Pont R, Brodbelt DC, Church DB, Pegram C, Mustikka M. Breed and conformational predispositions for prolapsed nictitating membrane gland (PNMG) in dogs in the UK: A VetCompass study. PLoS One. 2022;17(1):e0260538. PMID: 35081121. PubMed
2. Zwueste DM, Grahn BH. A review of Horner's syndrome in small animals. Canadian Veterinary Journal. 2019;60(1):81–88. PMID: 30651655. PubMed
3. Saito A, Izumisawa Y, Yamashita K, Kotani T. The effect of third eyelid gland removal on the ocular surface of dogs. Veterinary Ophthalmology. 2001;4(1):13–18. PMID: 11397314. PubMed
4. Eye Structure and Function in Dogs. Merck Veterinary Manual, Dog Owners edition. merckvetmanual.com
5. Cherry eye in dogs. Riney Canine Health Centre, Cornell University College of Veterinary Medicine. vet.cornell.edu

This article is for general educational purposes and does not replace professional veterinary advice, diagnosis or treatment. If your dog's third eyelid is showing along with pain, discharge or changes in the eye, contact your veterinarian. Pure Majesty Pets products support routine eye hygiene and everyday comfort; they are not medicines and do not treat, cure or prevent cherry eye, Horner's syndrome, eye infections or any other condition.