Here's an uncomfortable fact worth knowing upfront: cats are so good at hiding pain that a cat with genuinely severe, ongoing eye pressure can still eat, groom, and greet you at the door like nothing is wrong. Glaucoma is a real medical emergency in cats, and one of the biggest obstacles to catching it in time isn't a lack of information it's that your cat simply won't act the way you'd expect a creature in pain to act.

Glaucoma occurs when an imbalance in the production and drainage of fluid inside the eye causes pressure to build up to unhealthy levels, and in cats unlike dogs it's less common but usually develops secondary to inflammation inside the eye or a tumour, rather than as a standalone condition. The pressure itself can destroy the retina and the optic disk, permanently affecting vision, and it needs to be brought down as quickly as possible to limit the damage. Understanding both the subtle warning signs and why speed matters so much here is genuinely one of the more valuable things a cat owner can know.

Key Takeaways

• Glaucoma happens when fluid inside the eye isn't draining properly, causing pressure to build to damaging levels.
• Glaucoma is less common in cats than in dogs, and it usually develops secondary to uveitis or a tumour rather than occurring on its own though primary glaucoma does happen, particularly in Siamese cats.
• Early signs include a dilated, unmoving or slow-moving pupil, redness in the whites of the eye, corneal swelling or discolouration, and a firm-feeling eyeball.
• Cats with glaucoma usually show pain through behaviour changes, not obvious winking or squinting — this is a genuinely important, easy-to-miss detail.
• Any sign of glaucoma needs a same-day vet visit, since reducing eye pressure quickly is what limits permanent damage.
• Glaucoma usually needs long-term, ongoing management, and if the affected eye is permanently blind and painful, surgical removal may ultimately be the kindest option.

What Is Glaucoma in Cats?

Cats, like people, can develop glaucoma. It occurs when an imbalance in the production and drainage of fluid in the eye (aqueous humor) causes a buildup that increases eye pressure to unhealthy levels. The increased pressure can cause destruction of the retina and the optic disk the specific spot where the optic nerve enters the eye which is exactly why unmanaged glaucoma leads to permanent vision loss.

Is Glaucoma Common in Cats?

Genuinely, no glaucoma occurs less often in cats than in dogs. When it does occur, it usually develops after inflammation of the anterior uvea (uveitis) or a tumour inside the eye, rather than arising on its own. Primary (open-angle) glaucoma does happen independently too, particularly in the Siamese breed worth knowing if you share your home with one.

This connection to uveitis matters enormously, and it's worth understanding the chain here: uveitis is itself frequently the only visible sign of a serious underlying illness in cats, and glaucoma can develop as a downstream complication of that same inflammation if it isn't controlled. Our guide on uveitis in cats covers this underlying condition in more depth, since treating it properly is often exactly what prevents glaucoma from developing in the first place.

What Are the Signs of Glaucoma in Cats?

Initial signs of glaucoma include a dilated, unmoving or slow-moving pupil; redness in the whites of the eyes; swelling and discolouration of the cornea; and a firm eyeball. Prolonged increases in eye pressure can lead to further, more visible changes: enlargement of the eyeball itself, displacement of the lens, and breaks in a membrane of the cornea.

Why Is Glaucoma So Easy to Miss in Cats?

This is genuinely the most important, and most counter-intuitive, thing to understand about feline glaucoma. Pain usually shows itself as behavioural changes and occasional discomfort around the eye, rather than through spasmodic winking the obvious squinting most people associate with a painful eye. In other words, a cat in genuine pain from elevated eye pressure might not squint dramatically at all. They might simply become a bit more withdrawn, less affectionate, groom themselves less, or seem subtly "off" in ways that are genuinely easy to write off as a mood or a slow day.

This is exactly why the physical signs listed above the pupil, the redness, the corneal changes, the firmness of the eye itself matter so much as objective things to check, rather than relying on your cat to "tell you" through obvious distress the way a dog more typically might.

Why Is Glaucoma a Genuine Emergency?

If your cat displays any signs of glaucoma, it should be seen by a vet immediately. It's genuinely important to decrease the pressure within the eye as quickly as possible to minimise damage every hour of elevated pressure is doing further, potentially permanent harm to the retina and optic nerve. This isn't a "let's monitor it for a few days" situation; it's one where speed directly determines how much vision, if any, can ultimately be preserved.

How Is Glaucoma Diagnosed in Cats?

Diagnosis relies on measuring the pressure inside the eye using a specialised instrument called a tonometer (sometimes referred to by the brand name Tonopen), a quick, generally well-tolerated test performed during an eye exam. Normal eye pressure in cats typically falls in the range of roughly 15 to 25 mmHg, and any sustained pressure meaningfully above this range points toward glaucoma. Because glaucoma so often develops secondary to another condition, your vet will also want to investigate further once pressure is confirmed elevated checking for uveitis, tumours, or other underlying drivers, since treating the root cause is just as important as bringing the pressure down.

How Is Glaucoma Treated in Cats?

Treatment may require a combination of surgery and medications to reduce eye pressures, preserve vision, and manage pain. In cats with glaucoma caused by anterior uveitis specifically, it's necessary to reduce the inflammation and treat the underlying cause directly addressing the pressure alone, without treating what's actually driving the inflammation, isn't a complete solution.

In practice, this often means a layered approach: medications that reduce fluid production or improve drainage (commonly eye drops containing ingredients like dorzolamide or timolol), pain relief, and, in urgent situations with very high pressure, faster-acting treatments to bring pressure down quickly and protect against imminent vision loss. If uveitis is the underlying driver, anti-inflammatory treatment becomes a genuine, non-negotiable part of the plan, not an optional add-on.

Does Glaucoma Ever Go Away for Good?

Not typically glaucoma usually requires long-term management rather than a single treatment that resolves it permanently. This is genuinely important to plan for emotionally and financially: ongoing medication, regular pressure checks, and ongoing monitoring for the underlying cause are usually part of the picture for the long haul, not just the initial emergency visit.

What Happens If the Eye Is Already Blind?

If the affected eye is permanently blind, surgery may be performed to remove the painful eye. This can understandably feel like a difficult decision, but it's worth understanding it as a genuine relief measure rather than a last resort born of failure an eye with uncontrolled, chronically high pressure is a source of ongoing pain even once vision is gone, and removing it directly addresses that pain in a way medication alone often can't once the eye is no longer salvageable. Most cats adapt remarkably well to life with one eye, or with vision loss overall, once the underlying source of pain and pressure is actually resolved.

What Should You Do If You Suspect Glaucoma?

• Go to the vet the same day, not the next available routine appointment, if you notice any of the signs above as covered throughout, speed genuinely limits permanent damage here.
• Don't rely on your cat's behaviour alone to judge severity. As covered above, pain often shows up subtly rather than through obvious squinting, so the physical signs matter more than how distressed your cat seems to be.
• If your cat has been diagnosed with uveitis, take the full treatment course seriously, since controlling that inflammation is a genuine protective step against glaucoma developing as a complication.
• If your cat is a Siamese, be aware this breed carries a specific, documented higher risk of primary glaucoma, worth mentioning at routine check-ups even without obvious symptoms.
• Never attempt a home remedy or use a leftover eye product. Our guide on human medicines and pets explains why this can genuinely worsen an already urgent eye emergency, and why the specific medications used for glaucoma need precise veterinary dosing.
• Understand your cat's baseline eye anatomy. Our guide on how a cat's eye works explains the normal fluid production and drainage system that glaucoma disrupts.
• Don't confuse glaucoma with a simpler eye problem. Our guide on cornea problems in cats covers other conditions that can cause a cloudy or discoloured eye, and a proper vet exam is genuinely the only reliable way to tell them apart.

FAQ

Can glaucoma in cats be cured?
Not usually it typically requires ongoing, long-term management rather than a single cure, particularly once vision has already been affected. Early treatment, though, can meaningfully preserve vision and comfort for a genuinely long time.

Is glaucoma painful for cats?
Yes, genuinely, even though cats rarely show it through obvious squinting or crying. Pain usually presents as subtle behaviour changes instead, which is exactly why the physical eye signs matter so much for actually catching it.

Can one eye have glaucoma while the other stays normal?
Yes, and this is part of why it can go unnoticed for a while a cat with normal vision in one eye can compensate remarkably well, masking the fact that the other eye is genuinely struggling. Both eyes should be checked and pressure-tested even if only one looks obviously affected.

Will my cat go blind from glaucoma? 
It's a genuine risk if pressure isn't brought down quickly, since sustained high pressure damages the retina and optic nerve. Prompt treatment meaningfully improves the odds of preserving vision, which is exactly why same-day veterinary attention matters so much.

Why does my vet want to know if my cat has had eye inflammation before?
Because glaucoma in cats usually develops secondary to uveitis or a tumour rather than occurring on its own, a history of eye inflammation is a genuinely relevant clue that helps your vet understand both the cause of the current pressure elevation and how to prevent it recurring.

References

1. Gelatt, Kirk N. Glaucoma in Cats. Merck Veterinary Manual, Pet Owner Version.
2. Glaucoma in Cats. VCA Animal Hospitals.