When to see a vet urgently
A sudden rise in eye pressure can damage sight quickly. Contact a vet immediately if you notice these changes:
- The eye becomes cloudy or bluish and the pupil remains large.
- Your cat shows eye discomfort, rubs their face or withdraws in obvious pain.
- Your cat begins bumping into things or seems to have lost sight suddenly.
- The eye becomes very red or looks larger than before.
Do not wait for every symptom to appear. You can find a vet near you.
Overview
Eye pressure is maintained through a balance between fluid production and drainage. In glaucoma, this balance is disrupted: fluid is produced normally but cannot drain adequately. Pressure rises, compressing the optic nerve and retina and eventually leading to permanent sight loss.
The fluid here is aqueous humour, which circulates inside the eye, rather than tears on its surface. It supplies nutrients to the cornea and lens and drains mainly through the angle between the cornea and iris. In glaucoma, the problem usually involves the drainage route rather than unusually high fluid production.
Sight loss does not mean that every newly diagnosed eye is already blind. Treatment aims to limit further damage. However, destroyed optic nerve tissue cannot be restored, so lowering pressure and recovering sight are not the same thing.
Causes
Glaucoma is divided into:
- Primary: associated with inherited abnormalities of the drainage angle in the anterior chamber; less common.
- Secondary: develops as a result of other diseases, such as:
- chronic uveitis, or inflammation within the eye;
- cataracts;
- injuries;
- tumours inside the eye;
- displacement of the lens;
- infections, including viral infections.
Secondary glaucoma is much more common than primary glaucoma in cats. Inflammatory material and scarring can impair drainage in an inflamed eye. Bleeding within the eye can also block the drainage route. Mentioning cataracts in the list therefore does not mean every cloudy lens leads to glaucoma: what matters is whether eye structure changes, inflammation develops or fluid flow is obstructed.
Uveitis may have an infectious or another inflammatory cause, but the cause is not always found. Investigation of eye inflammation and raised pressure therefore forms a combined assessment.
Risk factors
- older cats;
- certain breeds, including Siamese, Burmese and Persians;
- chronic eye disease;
- eye injuries.
Information on breed-specific risks in cats is limited, and the list should not be interpreted as a definite ranking of every breed. A predisposition to the rare primary form has been described in Siamese and Burmese cats. Secondary glaucoma is more often associated with eye disease in middle-aged and older cats, and an ordinary domestic cat is not protected from it.
Symptoms
Glaucoma may initially cause no symptoms. As it progresses, signs include:
- a dilated pupil with a poor response to light;
- corneal cloudiness or a hazy eye;
- redness of the sclera and enlarged blood vessels;
- eye pain, with face rubbing and avoidance of touch;
- reduced appetite and activity because of pain;
- enlargement of the eyeball from prolonged pressure;
- gradual or sudden sight loss.
Eye pain in a cat may appear as changed behaviour rather than constant squinting. Your cat may hide, be quieter than usual or avoid having their head touched. Watering can also occur. Conversely, familiar movement around the home may continue despite considerable discomfort and reduced sight. Normal movement alone therefore does not rule out disease.
Glaucoma cannot be confirmed from the eye's appearance. Cloudiness and redness may also involve other eye diseases needing different treatment. Your observations of when the change began and whether one or both eyes are affected help plan the investigation.
Possible complications
Glaucoma can lead to:
- optic nerve atrophy and permanent blindness;
- chronic pain;
- secondary inflammation;
- reduced quality of life.
Veterinary investigations
Diagnosis is based on:
- tonometry, or measuring eye pressure;
- ophthalmoscopy to assess the retina and optic nerve;
- gonioscopy to assess the anterior chamber angle;
- eye ultrasound when corneal cloudiness or tumours are present.
Tonometry assesses pressure inside the eye using a dedicated instrument. It complements examination of eye structures and sight rather than replacing them. Examination of the back of the eye looks for pressure-related changes in the retina and optic nerve region. The retina converts light into nerve signals that the optic nerve carries to the brain.
Examining the drainage angle helps assess the fluid outflow route and disease type. Specialised imaging can show structures at the front of the eye in more detail. The choice of investigations depends on routine examination findings and the likely underlying cause. Not every cat needs every investigation mentioned in the same way.
Eye pressure can also vary throughout the day. The vet therefore interprets a measurement alongside other findings and previous results. A follow-up visit is valuable for more than one reading: it also assesses whether the retina or optic nerve has changed. If needed, a vet experienced in eye disease adds methods that show internal structures in greater detail.
How the disease progresses
Glaucoma may develop slowly with sight loss, or suddenly, with pressure rising rapidly and sight disappearing within hours or days.
Slowly developing disease may already be advanced when you notice a change. Primary glaucoma usually affects both eyes, although symptoms need not appear simultaneously. The secondary form may remain in one eye or involve both. The prognosis for the other eye therefore cannot be inferred solely from how badly the first is affected.
Treatment and follow-up
Treatment aims to lower pressure, relieve pain and address any underlying disease. Medication is often central to care in cats. Some eye medicines reduce aqueous humour production. Glaucoma associated with inflammation may also require treatment of that inflammation in a way chosen by the vet.
A suitable medicine for a cat cannot be inferred from a human or dog prescription. The effectiveness and adverse effects of different medicine groups vary between species: some drainage-promoting medicines used in dogs, for example, work poorly in cats. Your cat's other illnesses also affect the choice. The vet prescribes the product and its use individually.
Repeat examinations and pressure measurements monitor effectiveness. Frequent visits may initially be needed to establish whether the chosen treatment is sufficient. A calmer-looking eye does not alone show that pressure is controlled. Medication may need changing, and long-term treatment is common.
Surgery is considered in difficult cases. If sight has been permanently lost and the eye is painful, removing it may relieve pain. The procedure then aims to improve your cat's comfort; it does not restore lost sight. Eye findings, pain control and the nature of the underlying disease affect the decision.
Cats can be sensitive to adverse effects of some pressure-lowering medicines. Tell the treating vet if appetite decreases or your cat's condition changes during treatment. Changing a medicine or its administration is the vet's responsibility, because untreated high pressure also endangers the eye. Bring information about all medicines your cat uses so their suitability can be assessed together.
Giving eye drops at home
Ask the practice to demonstrate administration. Another person's help may be needed when handling a painful cat. Calm, gentle support helps keep the head still. Wrapping your cat in a towel with the head exposed may make handling easier.
Do not let the bottle tip touch the eye. Hold the bottle steadily and follow the particular product's instructions, including any need to mix it. Do not change prescribed use according to how the eye looks.
Brief blinking or drooling may follow drops because some medicine travels through the tear ducts to the mouth. If rubbing continues or the eye becomes redder and more irritated afterwards, ask your vet what to do before the next administration.
Prevention
- regular eye examinations, particularly for breeding and older cats;
- treatment of chronic eye diseases, including uveitis and cataracts;
- prevention of eye injuries;
- prompt veterinary attention when eye changes appear.
What it means for owners
Glaucoma is a serious eye disease that can cause complete, permanent blindness. Owners should remember:
- early detection is crucial;
- any change in eye appearance warrants urgent veterinary examination;
- appropriate treatment can slow progression and preserve sight for longer.
This material provides information and does not replace veterinary care. If your cat develops symptoms, contact a vet immediately.
Frequently asked questions
Can glaucoma be cured completely?
Nerve damage caused by glaucoma is permanent. Treatment can nevertheless lower pressure, relieve pain and, in some situations, slow deterioration of sight. The prognosis also depends on whether underlying inflammation or another eye problem can be controlled.
Can only one eye be affected?
Yes. Secondary glaucoma can affect just one eye, and the other may never develop it. The primary form usually involves both eyes. Establishing the type helps assess monitoring needs for the other eye too.
Does a blind eye still need treatment?
Yes, because a blind eye can remain painful. An absence of sight does not remove the need to assess pressure and pain control. If pain cannot be controlled adequately, the vet may recommend removing the eye.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Feline Glaucoma, Cornell University College of Veterinary Medicine, accessed 2026-11-02.
- Glaucoma in Cats, Merck Veterinary Manual, accessed 2026-11-02.
- Glaucoma in Animals, Merck Veterinary Manual, accessed 2026-11-02.
- Treatment of Glaucoma in Animals, Merck Veterinary Manual, accessed 2026-11-02.
- Glaucoma in Cats, VCA Animal Hospitals, accessed 2026-11-02.
- Applying Eye Drops to Cats, VCA Animal Hospitals, accessed 2026-11-02.
