A little redness in the eye. Some squinting. Maybe your dog or cat is sleeping more than usual, or pulling away when you touch the side of their head. Most pet parents assume it’s a passing irritation.
The hard truth is that some of those signs can mean something much more serious — a painful, vision-threatening eye disease called glaucoma. And once it starts, the window to save your pet’s sight can close in hours.
Glaucoma is one of the most painful and vision-threatening eye diseases a dog or cat can develop. One veterinary ophthalmologist describes the pain as similar to a migraine headache — a level of discomfort most pet parents probably cannot fully imagine. Pets in this kind of pain may rub or paw at their face, become lethargic, stop eating, or just hide.
What Glaucoma Actually Is
Your pet’s eye is filled with a clear fluid called aqueous humor. It is constantly being produced inside the eye and drained out through a tiny structure called the iridocorneal angle, also known as the drainage angle. As long as production and drainage stay balanced, the pressure inside the eye — called intraocular pressure, or IOP — stays normal.
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Glaucoma happens when that drainage system fails. Fluid backs up and pressure builds. The structures inside the eye, particularly the retina and the optic nerve, which carry visual signals to the brain, start to take damage. It is important to know that glaucoma is not caused by the eye making too much fluid. It is caused by the fluid having nowhere to go.
If left untreated, glaucoma can cause irreversible blindness in just hours to days. Damage to the optic nerve is permanent — once vision is lost, it does not come back. In cats, vision is often impacted by the time symptoms are visible to pet parents, and if the condition is not treated within the first 48 hours, the cost is often full loss of their sight.
The 2 Forms of Glaucoma
Not all glaucoma is the same — and understanding which type your pet has shapes both the treatment plan and what to watch for in their other eye. Glaucoma comes in two main types.
Primary glaucoma is inherited or congenital. It happens in an otherwise healthy eye because of anatomical abnormalities in the drainage angle. Certain dog breeds are predisposed, and in cats, Siamese, Burmese, and Persian breeds are most commonly affected.
Secondary glaucoma develops because of another problem inside the eye or a systemic problem in the body. This is the slightly less common form in dogs, and the most common cause in cats, comprising more than 90% of cases. Triggers include uveitis — inflammation inside the eye, where debris and scar tissue block drainage — lens dislocation, tumors or cancer inside the eye, internal eye bleeding, and lens damage that releases proteins.
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This distinction matters more than most owners realize. A dog born with a faulty drainage angle faces a different long-term outlook than a cat whose glaucoma stems from an infection like FIV or FIP. Treating the root cause in secondary cases can sometimes halt the pressure buildup entirely, whereas primary glaucoma typically requires lifelong management.
Genetics plays a big role in who develops primary glaucoma. Many dog breeds are predisposed, including Cocker Spaniels, Basset Hounds, Beagles, Boston Terriers, Chow Chows, Great Danes, Shar Peis, Shih Tzus, Siberian Huskies, Akitas, and Samoyeds. In cats, glaucoma is rarer overall but tends to affect middle-aged or senior cats in cases of secondary glaucoma.
Signs to Watch For
In acute glaucoma, the signs come on suddenly. In chronic cases, they build up more slowly and may have been present for some time before you notice anything is wrong. Eye pain — your pet may squint, partially close the eye, or rub at it — is common. Other signs include turning away or flinching when you touch the side of their head, watery discharge, redness in the white of the eye, a cloudy or bluish appearance to the cornea, a dilated pupil that does not respond to light, visible swelling or bulging of the eyeball, sudden vision loss, lethargy, and behavior changes in cats.
If you see any combination of these — particularly the redness, cloudiness, sudden vision changes, or signs of pain — treat it as an emergency. Call your veterinarian or head to an emergency clinic right away.
How It Is Diagnosed and Treated
Glaucoma is diagnosed by measuring intraocular pressure with a device called a tonometer, along with an internal exam of the eye using specialized instruments. For acute cases, your veterinarian may refer you to a veterinary ophthalmologist for the most specialized care. Time matters at this stage — the faster the pressure can be brought down, the better your pet’s chances of keeping their vision.
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Treatment focuses on two things at once: relieving the pain and bringing the pressure down as quickly as possible. Pain relievers help with discomfort, and prescription eye drops or oral drugs work to either decrease fluid production or promote drainage. Long-term medical therapy may involve carbonic anhydrase inhibitors or beta-adrenergic blocking agents. These medications are often a long-term commitment, not a short-term fix.
For severe or advanced cases, veterinary ophthalmologists may use various surgical techniques to lower pressure. These can include a glaucoma valve placement, a laser procedure, or — in eyes that have already lost vision — removal of the eye to end the pain. Some pets are good candidates for a prosthetic eye. If secondary glaucoma is driving the problem — a tumor, severe uveitis, lens dislocation — addressing the root issue is critical.
Glaucoma typically requires ongoing care. Once it is diagnosed, your veterinarian will likely want frequent follow-ups to make sure the treatment is working and to adjust medications as needed. Even with successful treatment, regular checkups remain important, because glaucoma can develop in the second eye over time, even if it started in only one. The prognosis depends largely on the underlying cause. Many pets do well with consistent care, especially when the condition is caught early.
Glaucoma is the kind of emergency that is easy to miss because it can look like something minor at first — a touch of redness, a little squinting, a quieter day than usual. But behind those small signs can be a level of pain your pet cannot tell you about, and a clock that is already ticking on their vision. The good news is that early intervention can save sight, relieve pain, and protect your pet’s quality of life. If your pet’s eye suddenly looks red, cloudy, or painful, do not wait. With glaucoma, hours really can be the difference between vision saved and vision lost.
