Glaucoma is an increased pressure inside the eye, caused by an obstruction to the drainage of the fluid from within the eye. In order to keep the eye inflated, fluid is normally produced and cleared away from the eye all the time. The fluid inside the eye is not related to the tear fluid (which is on the surface of the eye).
North Carrollton Veterinary Hospital uses a special instrument called a tonometer to measure the pressure inside the eye. Local anesthetic is applied to the eye for this test which is usually very well tolerated.