Why is my dog squinting or keeping one eye closed?

Squinting or keeping one eye closed (blepharospasm) is a sign of pain or discomfort. Common causes include a corneal scratch or ulcer, foreign body in the eye (grass seed, eyelash), conjunctivitis, glaucoma, or uveitis. Don't delay on this — a corneal ulcer that's left untreated can progress to a perforation. Same-day or next-day evaluation is appropriate for significant squinting.

What is KCS (dry eye) in dogs?

KCS (keratoconjunctivitis sicca), or dry eye, is a condition where the tear glands don't produce adequate tears. Signs include thick, mucus-like discharge, red irritated eyes, and a dull corneal appearance. It's very common in certain breeds — Cocker Spaniels, Shih Tzus, Bulldogs, Pugs. It requires lifelong management with eye drops (cyclosporine or tacrolimus) to prevent corneal damage.

What is glaucoma in dogs?

Glaucoma is increased pressure inside the eye (intraocular pressure). Acute glaucoma is extremely painful and causes rapid, severe damage. Signs: sudden onset of squinting, red eye, cloudiness, possible enlarged eyeball, apparent pain. This is an emergency. Untreated acute glaucoma causes permanent vision loss within 24–72 hours. If your dog suddenly has a red, painful, cloudy eye — come in immediately or go to an emergency vet.

Are eye drops for humans safe for dogs?

Not in general. Plain saline eye rinse can be used to flush debris from an eye. But medicated eye drops designed for humans — including over-the-counter redness relief drops (which contain vasoconstrictors) — should not be used in dogs without veterinary guidance. Some human eye drops contain ingredients toxic to dogs. When in doubt, call us before using anything.

Why does my dog have red eyes?

Red eyes in dogs can indicate conjunctivitis, dry eye, a foreign body, uveitis (internal eye inflammation), glaucoma, cherry eye, or systemic illness. Mild redness after outdoor play or a dusty environment can be benign. But persistent or significant redness, especially with discharge, squinting, or cloudiness, should be evaluated promptly.

Dog Eye Problems: Common Causes and When to See a Vet

Q: What causes eye discharge in dogs?

Eye discharge in dogs has many causes. Clear, watery discharge is often from allergies, irritants, or a blocked tear duct. Yellow or green discharge usually indicates bacterial infection or conjunctivitis. Thick, mucus-like discharge can be from dry eye (KCS). Any significant change in discharge, especially with redness or squinting, warrants veterinary evaluation.

Eyes are one of the areas where small changes can mean very different things — from "this is nothing" to "this is a same-day emergency." We see a lot of eye issues in dogs at our Alhambra clinic, and the questions owners ask most often are exactly the right ones: is this serious? Should I come in today? Can I wait until tomorrow?

Here's how to read what you're seeing.

Eye discharge: reading what it tells you

Clear, watery discharge: Often benign. Allergens, dust, wind, and mild irritants cause watery eyes in dogs the same way they do in people. Common in LA's dry, sometimes smoky air. If it's just watery and the eye looks otherwise normal — no redness, no squinting, no cloudiness — it can often be monitored. If it persists more than a few days, worth a look.

Yellow or green discharge: Suggests bacterial involvement. Conjunctivitis (bacterial infection of the conjunctiva) is the most common cause. Eyes may be red, and the dog may be rubbing at them. This doesn't resolve without treatment — needs antibiotics, usually in the form of eye drops or ointment. Don't wait this one out.

Thick, ropy, mucus-like discharge: Think KCS (dry eye — see below). This is a distinctive type of discharge, often gray or yellowish-white, that builds up at the inner corner and is harder to wipe clean than normal discharge. It's a chronic condition that requires ongoing management, not just a one-time treatment.

Bloody or dark discharge: Less common, but any blood in or around the eye warrants prompt evaluation. Can indicate trauma, severe infection, or a mass.

Squinting or keeping one eye closed

This is one of the signs we tell owners not to wait on. Squinting (blepharospasm) indicates pain or irritation, and the differential list includes several conditions that progress quickly if untreated:

Corneal scratch or ulcer: The most common cause of sudden squinting in dogs. The cornea (clear surface of the eye) scratched or abraded — from a stick, a cat claw, a rough surface, or even a hair rubbing against it. Very painful. Diagnosed by putting fluorescein dye in the eye (it sticks to damaged corneal areas and glows). Treated with antibiotic eye drops and sometimes additional eye drops to prevent secondary infection and support healing. Don't delay — an untreated corneal ulcer can deepen into a perforation.
Foreign body: A grass seed, sand particle, or eyelash caught under the eyelid. Causes intense discomfort and squinting. Sometimes visible; sometimes not, and requires a slit lamp examination to see under the third eyelid.
Glaucoma: Increased intraocular pressure. Can cause sudden, severe squinting — often accompanied by a red eye, cloudiness, and visible pain. This is an emergency. Permanent vision loss can occur within 24–72 hours if not treated promptly.
Uveitis: Internal eye inflammation. Red eye, squinting, possible cloudiness. Can be a sign of systemic disease (tick-borne illness, immune-mediated conditions). Needs evaluation.

Red eyes

A slightly red eye after running through brush or on a dusty day — probably fine. Keep an eye on it. Persistent or significant redness, especially combined with discharge, squinting, or cloudiness? Come in.

Red eyes in dogs are commonly caused by:

Conjunctivitis (bacterial, viral, or allergic)
Dry eye (KCS)
Foreign body
Uveitis
Glaucoma (often a very red, painful eye)
Cherry eye (prolapse of the third eyelid gland — see below)

Cloudy eyes

Gradual cloudiness in older dogs: Nuclear sclerosis is an extremely common, normal aging change in which the lens of the eye develops a blue-gray haze. It doesn't affect vision significantly and requires no treatment. Dogs over 7–8 years old almost universally develop some degree of it. Often mistaken for cataracts — it's not.

Cataracts: A true opacity of the lens (looks white, not just hazy). Can develop with age, from diabetes, or from genetics. Significant cataracts affect vision. Surgical correction by a veterinary ophthalmologist is an option if the dog's overall health supports it.

Sudden cloudiness in a young dog or in one eye: More concerning. Glaucoma, uveitis, or corneal edema can all cause sudden cloudiness. If the cloudiness appeared quickly — same day or within a day or two — have it evaluated promptly.

Cherry eye

The "cherry eye" is the prolapsed gland of the third eyelid — a pink or red round mass visible in the inner corner of the eye. It looks alarming but isn't immediately painful in most cases. That said, it doesn't go back in on its own, and leaving it prolapsed risks drying out and damaging the gland permanently. Surgical repositioning (not removal) is the recommended treatment. We see this most often in young dogs under 2 — Bulldogs, Cocker Spaniels, Beagles, and Boston Terriers are especially prone.

KCS (Dry Eye)

Keratoconjunctivitis sicca — dry eye — happens when the tear glands produce insufficient tears. The result: thick, ropy discharge, red irritated eyes, and over time, damage to the corneal surface. It's a lifelong condition that requires daily eye drops (usually cyclosporine or tacrolimus) to manage the immune response that's destroying the tear glands. Without treatment, corneal scarring and vision loss occur.

Breed predisposition is real here. Cocker Spaniels, Shih Tzus, Bulldogs, Pugs, and a handful of other breeds are significantly more prone. If you have one of these breeds, ask about tear production testing at your annual exam.

Common owner mistakes

Using human eye drops. Plain saline rinse is fine for flushing debris. But redness-relief drops containing vasoconstrictors, medicated antibiotic drops for humans, and other human eye medications should not be used in dogs without veterinary direction. Call us first.

Waiting too long on squinting. We see this regularly. The owner waited two or three days on a squinting dog, and by the time they came in, a corneal ulcer that could have healed in 5–7 days had deepened significantly. Squinting means something hurts. Same-day evaluation is appropriate.

Assuming discharge is "just allergies." Allergies can cause watery discharge, but thick or colored discharge typically means an infection that needs treatment.

When to monitor vs. come in

Monitor at home: Mild clear discharge with no other symptoms. Slightly watery eyes after outdoor activity with no redness or squinting.

See us within 1–2 days: Yellow or green discharge. Cherry eye that just appeared. Mild redness with no squinting or cloudiness.

Come in today: Squinting or holding eye closed. Significant redness with pain or discharge. Sudden cloudiness. Eye appears swollen or the eyeball looks enlarged. Visible foreign body in the eye.

Emergency: Trauma to the eye. Sudden severe squinting with red, cloudy eye (possible glaucoma). Eyeball appears to be protruding (proptosis — rare but a true emergency).

We see dogs for eye exams at South Pasadena Animal Hospital in Alhambra. Call (626) 441-1314 or check our services and pricing pages.

Frequently Asked Questions

What causes eye discharge in dogs?

Clear discharge: allergies or minor irritation. Yellow or green: bacterial conjunctivitis. Thick ropy: dry eye (KCS). Any significant discharge warrants a vet visit, especially if accompanied by redness or squinting.

Why is my dog squinting and keeping one eye closed?

Pain or discomfort — most commonly a corneal scratch or ulcer, but also foreign bodies, glaucoma, or uveitis. Squinting shouldn't be monitored at home for more than a few hours. It needs evaluation the same day if significant.

Is a cloudy eye in an older dog normal?

Bluish-gray cloudiness in older dogs is usually nuclear sclerosis — a normal aging change that doesn't significantly affect vision. White opacity (cataracts) is different and does affect vision. Sudden cloudiness of any kind should be evaluated promptly.

What is cherry eye in dogs?

A prolapsed gland of the third eyelid — appears as a pink or red round mass in the inner corner. Common in young dogs of certain breeds. Needs surgical repositioning; doesn't resolve on its own.

Dog Eye Problems: What Each Symptom Usually Means