Uveitis vs Glaucoma in Dogs: How to Tell Them Apart

Uveitis is inflammation inside the eye, and it usually comes with a lower than normal eye pressure, a small constricted pupil and a deep red tinge to the white of the eye. Glaucoma is the opposite pressure problem: fluid cannot drain, pressure climbs, and the pupil is often wide and sluggish while the cornea turns a hazy blue. If your dog's eye has suddenly turned red, cloudy, squinty or bulging, call your veterinarian or an emergency clinic today rather than waiting to see how it looks in the morning, because high pressure can take sight away quickly.

The frustrating part for owners is that uveitis, glaucoma, cataracts and conjunctivitis can all produce the same first impression: something is wrong with that eye. The differences are real and readable, but a few of them need instruments. This page walks through what separates them, what you can reasonably judge at home, and what a veterinary exam adds.

Too much inflammation versus too much pressure

The eye constantly makes a clear fluid called aqueous humour in the ciliary body and drains it out through a filtration angle near the base of the iris. The balance between production and drainage sets the intraocular pressure, which a vet measures with a tonometer in a few seconds.

In uveitis, the uvea (the iris, ciliary body and choroid, the pigmented vascular layer of the eye) becomes inflamed. The blood-eye barrier leaks, so protein and white cells spill into the normally crystal-clear fluid, giving the inside of the eye a dull or smoky look that vets call aqueous flare. The inflamed ciliary body often makes less fluid, so pressure tends to fall. The iris muscle spasms, so the pupil usually becomes small. The dog is light-sensitive and squinty. Causes range from blunt trauma and corneal ulcers to tick-borne and fungal infections, immune-mediated disease, leaking cataracts and tumours inside the eye.

In glaucoma, the drainage angle fails. Pressure rises and presses on the retina and optic nerve. The cornea becomes waterlogged and takes on a diffuse blue-grey haze, the blood vessels on the white of the eye engorge, and the pupil typically dilates and responds poorly to light because the iris muscle is overwhelmed by pressure. Primary glaucoma is inherited and angle-related, and is seen more often in breeds such as cocker spaniels, basset hounds, beagles, chow chows, shar peis and Siberian huskies. Secondary glaucoma develops because something else blocked the drainage, and chronic uveitis is one of the most common reasons that happens.

A dog can have both conditions in the same eye, which is exactly why "it looks like uveitis to me" is never a reason to wait: only a pressure reading tells you which way the eye is going.

Side by side: glaucoma, uveitis, cataracts and conjunctivitis

Feature	Glaucoma	Uveitis	Cataract	Conjunctivitis
What is affected	Drainage angle, retina, optic nerve	Iris, ciliary body, choroid	The lens, behind the pupil	The pink lining of lids and eye
Eye pressure	High	Usually low	Normal unless complicated	Normal
Pupil	Often wide, slow to react	Often small, may look irregular	Normal, white opacity sits behind it	Normal
Cornea	Diffuse blue-grey haze over the whole surface	May be hazy, often with deep redness around the edge	Clear	Clear
Redness	Deep, large straight vessels on the white	Deep red ring around the cornea	None	Bright pink, fine branching vessels, swollen lining
Discharge	Usually little	Variable, often watery	None	Often significant, watery to mucky
Pain	Marked, often a headache-like dullness	Marked, squinting and light shyness	None	Mild irritation, itchy
Vision	Threatened, can be lost fast	Threatened if untreated	Reduced gradually, worse in dim light	Normal
Urgency	Emergency	Same-day	Prompt exam, not an emergency alone	Prompt exam, worse if squinting

What you can actually see in a photo, and what photos miss

Searching for pictures is a reasonable instinct, and photo comparisons do help with one question in particular: where the cloudiness sits.

A cataract is an opacity of the lens, which sits behind the pupil. In a photo it looks like a white or pearly disc framed by the pupil opening, with the surface of the eye still glossy and clear in front of it. You can often see the sharp circular edge of the pupil around it.

Glaucoma-related cloudiness sits on the cornea, the front surface. It looks diffuse, bluish and smoky, as if someone breathed on glass, and it blurs the whole front of the eye rather than a neat circle in the middle. The eye often looks angry and bloodshot at the same time, and in longstanding cases the globe itself enlarges.

Age-related nuclear sclerosis is the great impostor. Most dogs over middle age develop a bluish-grey haze in the centre of the lens that is a normal hardening process, not a cataract, and it does not meaningfully take vision away. A vet can shine a light in and still see a reflection from the back of the eye through sclerosis, where a dense cataract blocks it.

Redness patterns photograph well too. Conjunctivitis produces bright pink, fine, branching vessels on the moveable lining of the lids and the white of the eye, usually with discharge, and the dog can still see normally. Glaucoma and uveitis produce deeper, straighter, darker vessels that look like they are emerging from under the surface. What a photo cannot show is pressure, flare, tear production or the back of the eye, so use pictures to decide how worried to be, not to decide what it is.

How each one is diagnosed and treated

A full eye workup is quick and mostly painless: pressure measurement, a fluorescein stain to find corneal ulcers, a tear production test, magnified examination of the front of the eye, and a look at the retina. Suspected glaucoma may add gonioscopy to assess the drainage angle, or an ultrasound if the eye is too cloudy to see through. Uveitis usually triggers a search for a cause, which can include bloodwork, infectious disease testing and imaging, because the eye is sometimes the first place a whole-body illness shows up.

Glaucoma treatment starts with lowering pressure urgently using topical and systemic medications, then maintaining it long term, often with referral to a veterinary ophthalmologist. Surgical and laser options exist to reduce fluid production or create new drainage. When an eye is permanently blind and painful, removal or an intrascleral prosthesis is offered as a pain-relief decision rather than a failure. In inherited glaucoma, the unaffected eye is frequently monitored and sometimes medicated preventively, because the second eye is at risk. Results vary from dog to dog, and vision already lost at the time of diagnosis is usually not recoverable.

Uveitis treatment has two halves: controlling inflammation with prescribed anti-inflammatory medication, and finding and addressing what set it off. Medications that relax the iris may be used, but only once pressure is known, because the same drug that comforts a low-pressure eye can be harmful in a high-pressure one. That is the practical reason home treatment goes wrong.

Cataract treatment is surgical. Phacoemulsification, the same technique used in people, removes the cloudy lens and usually replaces it with an artificial one, and it is performed by ophthalmology specialists after testing to confirm the retina still works. No drop or supplement dissolves a formed cataract. Diabetes is a common driver of rapidly forming cataracts in dogs. Mature cataracts can leak lens protein and trigger lens-induced uveitis, which in turn can block the drainage angle, so "just a cataract" still deserves periodic rechecks.

Conjunctivitis treatment depends on the cause: allergy, irritants, foreign material, dry eye or infection are all possibilities, and dry eye in particular is diagnosed with a tear test rather than guessed at. Never reach for leftover drops from a previous episode or from a human medicine cabinet. A steroid drop used on an eye with a corneal ulcer can make a manageable problem far worse, so talk to your vet before anything goes into the eye.

How canine glaucoma differs from the human and feline versions

People most often develop primary open-angle glaucoma: slow, painless and typically caught at a routine pressure check long before vision changes. Dogs more often develop angle-closure forms linked to an abnormally formed drainage angle, which present acutely, painfully and dramatically. One recognised exception is the inherited open-angle glaucoma documented in beagles, which has been studied as a model of the human disease. The practical consequence is that a dog rarely arrives early. By the time the eye is red and cloudy, pressure has usually been high for a while, which is why the emergency framing is not an exaggeration and why human eye drops and human dosing are not transferable.

Cats sit somewhere else again. Primary glaucoma is uncommon in cats, and most feline cases are secondary to chronic uveitis, which itself can be linked to conditions such as lymphoma, feline leukaemia virus, feline immunodeficiency virus and toxoplasmosis. Cats also hide it better: the eye tends to enlarge gradually rather than become acutely red and steamy, and the first thing an owner notices may be that one eye simply looks bigger, or that the pupil shape has changed. Any cat with a change in eye size, colour or pupil symmetry deserves an examination and a general health workup.

What if you are not sure how urgent this is

What if it is the weekend and the eye is cloudy and squinting

Treat squinting plus cloudiness plus redness as emergency-clinic territory. Pain and pressure do not keep office hours, and the cost of being wrong is vision.

What if a known cataract eye suddenly turns red

That combination suggests lens-induced inflammation or secondary glaucoma, not a worsening cataract. It needs a pressure check promptly rather than at the next scheduled recheck.

What if only one eye looks wrong

One-sided changes are common in glaucoma and uveitis and are easy to miss, since dogs compensate well. Compare the two eyes in the same light, from the front and from the side, and photograph them so you can show a change over time.

Key takeaways

• Uveitis means inflammation inside the eye, typically with low pressure and a small pupil. Glaucoma means high pressure, typically with a wide pupil and diffuse corneal haze.
• Untreated uveitis is a leading route to secondary glaucoma, so the two are linked rather than separate camps.
• Cataracts sit behind the pupil as a defined white opacity and are not painful. Corneal haze from glaucoma covers the whole front of the eye.
• Conjunctivitis is bright pink, discharge-heavy and vision-sparing. Deep red vessels with squinting point to something inside the eye.
• Nuclear sclerosis is the normal bluish haze of an ageing lens and is not a cataract.
• Cats mostly get secondary glaucoma from chronic uveitis, with subtler signs than dogs.
• No photo, app or home remedy substitutes for a tonometer reading.

Working with your veterinarian from here

Diagnosis and the treatment plan belong to your veterinarian, who can measure what you cannot see and decide which medications are safe for the pressure your dog's eye is actually running. Bring photos, note when the change started, mention any recent trauma, tick exposure, increased drinking or other illness, and ask directly whether a referral to a veterinary ophthalmologist is worth doing now rather than later. If you keep one rule from this page, make it this one: a painful, cloudy or red eye is examined today, not monitored at home.

For a wider list of signs that mean do not wait until morning, read Dog Emergency Signs, and browse related eye and whole-body topics in the conditions library.