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Glaucoma in Dogs and Cats


What is Glaucoma in Dogs and Cats?

Glaucoma in dogs and cats is increased pressure in the eye. The eye is approximately round, like an egg, but rather than having a hard shell like an egg, the eye has a soft flexible outer covering. The flexible eye would collapse except that it is kept expanded by fluid. The fluid is made within the eye at a steady rate and flows out of the eye through a canal at a steady rate. If too much intraocular fluid is made, or if the fluid cannot flow out through the canal, the pressure builds within the eye causing glaucoma.

Glaucoma in pets can lead to blindness and develop in your pet's other eye if not treated.
Key Facts of TOPIC NAME in Dogs and Cats
  • Glaucoma is usually due to a health problem that begins outside the eye, such as an infection
  • Glaucoma can be very painful
  • Glaucoma causes blindness


How Eyeball Pressure Relates to Glaucoma in Dogs

Normal pressure for dogs is approximately 25 mmHg. Normal pressure for cats is approximately 30 mmHg. Eyeball pressure is low compared with blood pressure. For example, the circulating blood always has a pressure about 80 mm Hg; and in dogs and cats, the blood pressure rises to 140 or 170 mmHg when the heart contracts. Pet eyeball pressure is measured with a tonometer, just as it is measured for humans.

Eyeball pressure in health and disease in dogs

There may be small differences in pressure from one eye to the other, from one day to another, from one hour to another.


Normal intraocular pressure (IOP)




Anterior uveitis (inflammation)


Anterior uveitis & secondary glaucoma



Two Forms of Glaucoma in Dogs and Cats

Primary Glaucoma

Primary glaucoma is caused by a problem either with fluid flow within the eye or with flow out through the eye canal. Most pets with primary glaucoma have too narrow an angle for the fluid to flow easily out of the eye. With primary human glaucoma, the opposite occurs: the outflow angle is wide.

Secondary Glaucoma

Secondary glaucoma is caused by a disease that affects the eye so that the eye responds by making too much fluid or by developing a problem with fluid outflow. For example, if your pet has a systemic fungal infection (toxoplasmosis, histoplasmosis, blastomycosis or cryptococcosis) the infection affects the eye, causing glaucoma. If your pet was hit by a car and the lens within the eye was shaken loose, the lens can block fluid flow and create glaucoma. With secondary glaucoma, it is as important to treat the underlying cause as it is to treat the glaucoma itself.

What Causes Most Cases of Glaucoma in Dogs and Cats?

Your pet is twice as likely to develop secondary glaucoma—have another health problem that causes the pressure within the eye to increase—than to develop primary glaucoma.

Why Glaucoma in Dogs and Cats is Bad

Glaucoma can be so painful that humans say it is a 12 on a scale of 1-10. Pain is caused by sudden changes in intraocular pressure or acute-onset glaucoma. Chronic glaucoma that develops slowly over time may not be painful.

Glaucoma is also bad because it leads to blindness. About 40% of dogs with glaucoma will be blind within a year regardless of glaucoma treatment. Although glaucoma can begin in one eye, 50% of pets with glaucoma develop the disease in the other eye unless they receive glaucoma treatment.

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(for Dogs)
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(for Dogs)


Which Pets Are Most at Risk for Glaucoma?

Cats seldom develop glaucoma, but many dog breeds are predisposed to glaucoma and should have their eyes checked twice a year: Akita, Basset Hound, Beagle, Chihuahua, Chow Chow, Cocker Spaniel, Dachshund, Fox Terrier, Maltese, Norwegian Elkhound, Poodle, Siberian Husky, Welsh Springer Spaniel.


Max's Tip: When using a product such as Timolol, do not touch the dropper to any surface, including eyes and hands. The dropper is sterile. If it becomes contaminated, it could cause an infection of the eye.  

Medical Terms for Glaucoma in Dogs and Cats Glaucoma Medical terms: intraocular, tonometer, uveitis, intraocular pressure (IOP), primary glaucoma, secondary glaucoma, corneal edema, tearing (epiphora), squinting (blepharospasm), enlarged eyeball (buphthalmos)

More Information on Glaucoma in Dogs and Cats

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