A squinting dog is almost always telling you something hurts. The medical term is blepharospasm, an involuntary tightening of the muscles around the eye in response to pain, irritation, or inflammation. It can range from a minor irritant that resolves on its own to a sight-threatening emergency, so the details matter. Here’s how to figure out what’s going on.
The Most Common Reasons Dogs Squint
The majority of squinting cases fall into a handful of categories, and most involve some form of direct eye irritation or injury.
Corneal ulcers are one of the top causes. These are scratches or open sores on the clear surface of the eye, often caused by rough play, running through brush, a paw swipe, or a foreign object like a grass seed lodged under the eyelid. Superficial ulcers typically heal within two to four weeks with treatment. Deeper ulcers take 10 to 30 days with medication, and older dogs tend to heal more slowly, sometimes needing up to 46 days. Deep ulcers that aren’t improving often require a minor surgical procedure in addition to eye drops.
Conjunctivitis (pink eye) causes redness, swelling of the tissue around the eye, and discharge. It can be triggered by allergies, bacteria, or viral infections. Dogs with conjunctivitis often squint, paw at their face, and produce noticeable discharge.
Uveitis is inflammation inside the eye itself. It causes significant pain, squinting, sensitivity to light, and sometimes a cloudy appearance to the eye. Uveitis can be triggered by infections, immune system disorders, or even cancer, making it one of the more serious causes on this list.
Glaucoma involves a dangerous buildup of pressure inside the eye. Normal eye pressure in dogs averages around 19 mmHg. When pressure spikes, the eye becomes extremely painful, and you may notice the eye looks larger, bulging, or has a bluish-cloudy tint. Acute glaucoma is a genuine emergency that can cause permanent blindness within hours.
Dry eye occurs when a dog doesn’t produce enough tears to keep the cornea moist. Without that protective layer, the surface dries out, becomes irritated, and is far more vulnerable to ulcers and infections.
Foreign bodies like foxtails, sand, or small debris trapped under the eyelid cause intense, sudden squinting. If your dog was fine an hour ago and is now holding one eye shut after being outside, this is a likely culprit.
What the Discharge Tells You
Pay attention to any discharge coming from the squinting eye, because its color is a useful clue. A small amount of clear or slightly reddish-brown material at the corner of the eye is normal. It’s just dried tears mixed with mucus and dust.
Yellow or green discharge is a different story. That color typically signals an active infection, especially when paired with redness and obvious discomfort like rubbing or pawing at the face. If you’re seeing colored discharge, your dog needs to be examined rather than watched at home.
Flat-Faced Breeds Are at Higher Risk
Breeds like Pugs, French Bulldogs, Shih Tzus, and Boston Terriers have a structural disadvantage when it comes to eye problems. Their eyes sit further forward in the skull, and their eyelid openings are often too large for the size of the eye. This combination means the eyelids frequently can’t close all the way, a condition called lagophthalmos. Some of these dogs literally sleep with their eyes partially open.
On top of that, flat-faced breeds often have reduced corneal sensitivity, meaning they blink less and may not react to irritation the way other dogs do. They can have a serious corneal injury without showing obvious pain. Their prominent nasal skin folds can also push hair directly against the eye surface, causing chronic irritation. When these dogs do develop corneal ulcers, the ulcers tend to progress faster and can become infected, deepen, or “melt” through the corneal layers, potentially threatening the entire eye. If you own a brachycephalic breed, even mild squinting warrants a prompt exam.
Squinting From Whole-Body Illness
Sometimes squinting isn’t really an eye problem at all. It’s a symptom of a disease affecting the whole body. Several tick-borne illnesses, including ehrlichiosis and Lyme disease, can cause inflammation inside the eyes. Canine distemper virus is another well-known cause of eye inflammation, typically accompanied by fever, nasal discharge, coughing, and neurological symptoms.
Fungal infections like blastomycosis and histoplasmosis, common in certain regions of the United States, can seed the eyes and cause uveitis as part of a widespread infection. Even heartworm disease and certain cancers, including lymphoma, can produce eye inflammation and squinting as secondary effects. If your dog is squinting and also seems generally unwell (lethargic, not eating, feverish), the eyes may be a window into a bigger problem.
What Happens at the Vet
An eye exam for a squinting dog is quick and mostly painless. The vet will likely start by looking at the eye with a bright light and magnification to check the eyelids, the surface of the eye, and the structures inside.
The most common diagnostic test is a fluorescein stain. A drop of bright orange-green dye is placed on the eye, and the vet shines a blue light on it. The dye sticks to any damaged area on the cornea but won’t adhere to healthy tissue, making ulcers and scratches light up clearly. This test also reveals how deep an ulcer goes: the deepest layer of the cornea doesn’t absorb the dye, so if a deep spot stays dark while everything around it glows, the ulcer has reached a critical depth.
The vet may also measure tear production with a small paper strip placed at the edge of the eye to check for dry eye, or use a handheld device to measure the pressure inside the eye if glaucoma is suspected. If the stain shows the eye surface is intact, the vet will use dilating drops and look deeper for signs of uveitis or other internal problems.
Signs That Need Same-Day Attention
Some situations can’t wait for a regular appointment. The following are considered ophthalmic emergencies:
- An eye that appears to bulge or pop forward, which can happen after trauma, especially in flat-faced breeds
- A visible cut or puncture on the eye surface
- Something stuck in or on the eye that you can’t easily flush out
- Sudden cloudiness, a blue-gray haze, or an obviously enlarged eye, which may indicate acute glaucoma
- Sudden blindness, where your dog is bumping into things or not tracking movement
- A rapidly worsening ulcer with increasing discharge, swelling, or a “melting” appearance to the cornea
Acute glaucoma and deep corneal ulcers can both lead to permanent vision loss or loss of the eye if treatment is delayed even by a day. A simple squint with no discharge and no other symptoms can reasonably be monitored for 12 to 24 hours, but anything on the list above should be seen immediately.
What Recovery Looks Like
For the most common cause, a superficial corneal ulcer, your dog will likely go home with antibiotic eye drops and possibly pain medication. You’ll need to apply drops several times a day, and your dog will probably need to wear a cone to prevent pawing at the eye. Most superficial ulcers heal within two to three weeks, though some stubborn ones can take a month or longer.
Deep ulcers are trickier. Infection and ongoing irritation are the main complications during healing, so follow-up exams with repeat fluorescein staining are standard. The vet is looking for the stain-positive area to shrink at each visit. If it isn’t shrinking, or if the ulcer is getting deeper, surgery becomes the next step. In some cases, the vet will place a protective flap of tissue over the ulcer to act as a natural bandage, shielding it from friction and keeping the surface moist while it heals.
For conditions like glaucoma or uveitis, treatment is typically ongoing. These are managed rather than cured, and your dog may need eye drops long-term to keep pressure or inflammation under control.