Glaucoma in Dogs and Cats: Recognising the Silent Thief of Sight

Glaucoma is a condition where the fluid inside the eye (aqueous humour) cannot drain properly, causing intraocular pressure (IOP) to rise. This elevated pressure compresses the retina and optic nerve, causing irreversible damage to the cells responsible for vision.

"Glaucoma is a true ophthalmic emergency. In dogs, we can see irreversible retinal damage within hours of pressure spiking — not days, not weeks, hours. Every minute counts. If your dog's eye suddenly looks red, swollen, or cloudy and they're in pain, get to a vet immediately. Time saved is vision saved." — Dr. Sarah Chen, DVM

Normal intraocular pressure in dogs and cats is 10–25 mmHg. In acute glaucoma, pressure can spike to 40–70+ mmHg. At these levels, permanent vision loss can occur within 24–48 hours.

Two Types of Glaucoma

• Primary glaucoma — an inherited structural defect in the drainage angle of the eye. The drainage pathway is abnormally narrow or closed from birth, and pressure rises gradually or suddenly. This is breed-related and the most common type in dogs
• Secondary glaucoma — caused by another eye disease that blocks drainage: lens luxation (displaced lens), uveitis (intraocular inflammation), intraocular tumours, trauma, or post-cataract-surgery complications. This is the most common type in cats

Understanding the type matters because primary glaucoma means the other eye is at risk too (it carries the same genetic defect), while secondary glaucoma's prognosis depends on treating the underlying cause. For an overview of eye conditions, see our common eye problems guide.

Primary glaucoma is strongly heritable. If you own one of these breeds, awareness of glaucoma signs could save your dog's sight:

High-Risk Dog Breeds

• Cocker Spaniels (American and English) — the most commonly affected breed; often develops between 5–9 years
• Basset Hounds — narrow drainage angles are nearly universal in this breed
• Siberian Huskies and Samoyeds
• Shar-Peis — combination of narrow angles and breed-specific eye anatomy
• Chow Chows
• Jack Russell Terriers
• Shih Tzus
• Arctic breeds — Norwegian Elkhound, Alaskan Malamute
• Springer Spaniels, Flat-Coated Retrievers

Cats and Glaucoma

Primary glaucoma is rare in cats. When cats develop glaucoma, it's nearly always secondary to:

• Chronic uveitis — the most common cause; linked to FIP, FIV, toxoplasmosis, lymphoma
• Lens luxation — the lens displaces and blocks the drainage angle
• Intraocular tumours — melanoma or lymphoma within the eye

Secondary glaucoma in cats tends to develop more gradually than the acute spike seen in dogs, but it still requires prompt treatment.

Risk Factors for Both Species

• Age — primary glaucoma typically manifests in middle-aged to older pets (5–10 years)
• Previous eye disease — chronic uveitis, lens luxation, or cataract surgery significantly increase risk
• Family history — if a parent or sibling has glaucoma, the risk is substantially elevated

Glaucoma presents differently depending on whether the pressure rise is sudden (acute) or gradual (chronic). Knowing both presentations is critical:

Acute Glaucoma — Emergency

Acute glaucoma is intensely painful. Signs appear suddenly, often within hours:

• Severe redness — the sclera (white of the eye) is deeply congested, not just pink but dark red
• Cloudy or blue-white cornea — corneal oedema from the high pressure forcing fluid into the corneal layers
• Dilated, fixed pupil — the pupil is large and doesn't constrict in bright light
• The eye appears larger or bulging — especially noticeable when comparing to the other eye
• Extreme pain — squinting, rubbing at the eye, head pressing, crying, lethargy, reluctance to eat or play
• Tearing — profuse watering from the affected eye

Chronic Glaucoma — Gradual

Chronic glaucoma may develop insidiously over weeks to months. Signs are subtler and often missed until significant vision loss has occurred:

• Progressive eye enlargement (buphthalmos) — the eye slowly stretches as pressure remains elevated; eventually becomes visibly larger than normal
• Lens luxation — the zonules (fibres holding the lens) stretch and break, causing the lens to shift position
• Optic disc changes — cupping of the optic nerve (visible only on ophthalmoscopic exam)
• Reduced vision — bumping into things on the affected side, difficulty catching treats, hesitance in dim light
• Subtle behavioural changes — clingy behaviour, reluctance to play, reduced activity

By the time chronic glaucoma causes obvious symptoms, substantial vision loss has usually already occurred — which is why screening high-risk breeds with regular pressure checks is so valuable.

Glaucoma treatment aims to reduce intraocular pressure quickly in acute cases and maintain it long-term. Treatment depends on whether vision is still present:

Emergency Treatment (Acute, Vision Present)

• IV mannitol — an osmotic diuretic that rapidly draws fluid out of the eye; works within 30–60 minutes
• Topical prostaglandin analogues — latanoprost eye drops dramatically increase fluid outflow; first-line emergency treatment
• Topical carbonic anhydrase inhibitors — dorzolamide reduces fluid production within the eye
• Topical timolol — a beta-blocker that decreases aqueous humour production
• Pain management — systemic pain relief (opioids, NSAIDs)

Long-Term Medical Management

Once the acute crisis is controlled, ongoing topical medications (typically dorzolamide/timolol combination + latanoprost) are used to maintain pressure. However, medical management alone is often insufficient long-term for primary glaucoma — most dogs eventually need surgical intervention.

Surgical Options (Vision Present)

• Laser cyclophotocoagulation — a laser destroys some of the ciliary body cells that produce aqueous humour, reducing fluid production. Can be performed with a diode laser (transclerally) or endoscopically
• Gonioimplant (shunt) — a tiny tube is inserted to create a new drainage pathway for aqueous humour. Success rates are variable

End-Stage (Blind, Painful Eye)

When vision is irreversibly lost and the eye is painful, the priority shifts to comfort:

• Enucleation (eye removal) — the most definitive pain relief. Most owners are initially horrified, but dogs and cats adapt remarkably well — and the relief from chronic pain is immediate and transformative
• Intrascleral prosthesis — the internal contents of the eye are replaced with a silicone sphere; the eye looks relatively normal but cannot see. Cosmetic option for owners who prefer it
• Chemical ablation — injection of gentamicin into the eye to destroy the ciliary body. Less invasive than surgery but less predictable

In primary glaucoma, the other eye carries the same genetic predisposition and will almost certainly develop glaucoma too — typically within 8–12 months of the first eye. Proactive management of the second eye is one of the most impactful things you can do:

Prophylactic Treatment for the Fellow Eye

• Once one eye develops primary glaucoma, most veterinary ophthalmologists start preventative topical medication (typically latanoprost) on the unaffected eye
• Studies show prophylactic treatment can delay the onset of glaucoma in the fellow eye by months to years
• Regular pressure monitoring (every 3–6 months) of the unaffected eye is essential

Screening for High-Risk Breeds

• Gonioscopy — a specialised lens is placed on the eye to directly visualise the drainage angle. This can identify narrow or closed angles before pressure rises. Recommended for all high-risk breeds before breeding and ideally as part of annual eye exams
• Tonometry — regular intraocular pressure measurement (ideally every 6–12 months for at-risk breeds). Many general practice vets have Tonovet tonometers that can perform this painlessly in seconds

What You Can Do at Home

• Know the emergency signs — sudden redness, cloudiness, dilated pupil, squinting, pain. Don't wait to see if it improves — go to the vet immediately
• Monthly eye comparison — photograph both eyes monthly and compare. Look for size asymmetry, redness, or cloudiness
• Avoid tight collars — studies show tight-fitting collars can transiently increase IOP in dogs; use a harness instead, especially for at-risk breeds
• Communicate with your breeder — if your dog develops primary glaucoma, inform the breeder so they can make informed breeding decisions

Glaucoma remains one of the leading causes of blindness in dogs, but with early detection through screening, prophylactic treatment, and rapid response to acute episodes, many dogs retain functional vision for years longer than they would without intervention. For guidance on supporting pets that have lost vision, see our cataracts and vision loss guide.