A dog holding one eye closed or squinting is almost always a sign of pain or irritation in that eye. The medical term for this involuntary squinting is blepharospasm, a spasmodic blinking or closing caused by the muscles around the eye contracting in response to discomfort. It’s one of the most reliable indicators that something is wrong, and the cause can range from a simple scratch to a serious condition that threatens your dog’s vision.
Foreign Objects and Surface Irritation
The most common reason a dog suddenly starts holding an eye shut is something stuck in or near the eye. In dogs, the most frequent culprits are organic plant materials: grass seeds, grass awns, small twigs, and bits of leaf or pollen. These tiny objects lodge under the eyelid or on the surface of the eye and cause immediate discomfort, tearing, and squinting. Less commonly, thorns, porcupine quills, or even small particles kicked up during play can scratch or penetrate the eye.
If a foreign body is sitting on the surface and hasn’t embedded itself, you can try gently flushing your dog’s eye with a sterile eye wash made for pets. Wash your hands before and after, and don’t touch the tip of the bottle to the eye or surrounding skin. If flushing doesn’t resolve the squinting within a short time, or if you can see something stuck in the eye, your dog needs professional help. Never try to pull an object out of the eye yourself.
Corneal Ulcers
A corneal ulcer is essentially a wound on the clear surface of the eye. Dogs with a corneal ulcer typically show tearing, squinting, redness, and rubbing at the affected eye. Ulcers can develop from a scratch, a foreign body, dry eye, or even contact with household chemicals. They’re painful and tend to get worse quickly if left untreated.
Your vet diagnoses a corneal ulcer by applying a special fluorescent dye called fluorescein to the eye’s surface. The dye sticks to damaged areas and glows bright green under a special light, clearly outlining the ulcer. Simple, shallow ulcers often heal within one to two weeks with antibiotic eye drops and pain management. Deep or “melting” ulcers are far more serious and may require surgical repair. In one study of dogs and cats with deep melting ulcers treated surgically, the average healing time was about 17 days, and vision was preserved in 90% of cases.
Entropion: Eyelids Rolling Inward
Some dogs are born with eyelids that roll inward, a condition called entropion. When this happens, the fur and eyelashes on the outer lid constantly rub against the surface of the eye, causing chronic irritation, squinting, and watery eyes. Over time, this friction can lead to corneal ulcers and scarring.
Entropion has a strong genetic component. Breeds with loose facial skin or prominent eyes are most predisposed, including Shar Peis, English Bulldogs, Bull Mastiffs, Chow Chows, Pugs, Labrador Retrievers, Golden Retrievers, Great Danes, Cocker Spaniels, Cavalier King Charles Spaniels, Boxers, and St. Bernards. If your dog is one of these breeds and has been squinting since a young age, entropion is a likely culprit. A vet can diagnose it with a standard eye exam, sometimes using a local anesthetic to make the exam more comfortable. Surgical correction is the usual fix and tends to resolve the problem permanently.
Dry Eye
Dogs can develop a condition where they don’t produce enough tears, officially called keratoconjunctivitis sicca. Without adequate tear production, the eye surface dries out, causing a gritty, burning sensation that makes the dog squint or paw at the eye. You might also notice a thick, yellowish discharge rather than clear tears.
Vets diagnose dry eye with a simple test that measures tear production by placing a small paper strip inside the lower eyelid for one minute and measuring how far the moisture travels. Treatment usually involves daily eye drops that either stimulate tear production or replace tears artificially. Most dogs with dry eye need lifelong management, but the condition is very controllable once identified.
Glaucoma and Uveitis
These are the conditions you don’t want to miss. Glaucoma occurs when fluid pressure inside the eye rises above normal levels. In dogs, normal eye pressure ranges from about 10 to 25 mmHg; glaucoma is diagnosed when pressure exceeds 30 mmHg. During the acute phase, the elevated pressure restricts blood flow inside the eye, causing congested blood vessels, a red and painful eye, and cloudy or hazy-looking cornea. The pupil often becomes dilated and unresponsive to light because the pressure paralyzes the muscle that constricts it. If the pressure stays elevated, the eyeball itself can begin to enlarge visibly.
Uveitis, or inflammation inside the eye, can look similar on the surface but involves different mechanisms. It can also lead to secondary glaucoma if the inflammation blocks the eye’s natural drainage pathways. Both conditions cause significant pain, and a dog with either one will squint, avoid light, and resist having the eye touched.
Acute glaucoma is a veterinary emergency. Without treatment within hours, the pressure can permanently destroy the optic nerve and cause irreversible blindness.
Signs That Require Immediate Attention
Not every squinting eye is an emergency, but certain signs mean your dog needs a vet the same day, or sooner:
- The eye is bulging or looks larger than the other eye. This suggests acute glaucoma or, in trauma cases, proptosis (the eye being pushed forward from its socket).
- You see blood inside the eye. This points to trauma or serious internal inflammation.
- The cornea looks cloudy, blue, or hazy. This can indicate corneal swelling from high pressure or a deep ulcer.
- Your dog suddenly can’t see. If your dog is bumping into things or not tracking movement, acute vision loss may be occurring.
- There’s a visible wound on the eyelid or eyeball. Lacerations to the eyelid or cornea need prompt surgical attention.
- The pupil looks different from the other eye. A fixed, dilated pupil suggests glaucoma; a very constricted pupil can indicate uveitis.
What You Can Safely Do at Home
If your dog just started squinting and appears otherwise comfortable, you can start by gently examining the eye in good lighting. Look for obvious redness, discharge, swelling, or anything visible on the surface. Don’t force the eye open if your dog is resisting, as this can cause more damage if there’s an ulcer or embedded object.
A gentle flush with a sterile pet eye wash can help clear out dust, pollen, or loose debris. Several over-the-counter sterile eye washes are available for dogs. Use them as directed, keep the bottle tip clean, and don’t apply any other eye medications unless your vet has prescribed them. Human eye drops, especially those designed to reduce redness, can contain ingredients that are harmful to dogs.
If the squinting doesn’t improve within a few hours after flushing, or if you notice any of the emergency signs listed above, the eye needs professional evaluation. Vets have tools that simply aren’t available at home: fluorescein dye to detect ulcers, tonometers to measure eye pressure, and magnification to spot tiny foreign bodies tucked under the eyelids. Many eye conditions in dogs are highly treatable when caught early, but they can become serious or irreversible when left for days.