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.
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Normal intraocular pressure (IOP) |
15-25mmHg |
Glaucoma |
25-30mmHg |
Anterior uveitis (inflammation) |
10-15mmHg |
Anterior uveitis & secondary glaucoma |
10-30mmHg |
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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