This aqueous humor is made inside the eye and passes from the eye at the same rate. This results in a stable intraocular pressure of 15-25 mm of Hg. Glaucoma is the consequence of a blockage of the outflow of aqueous humor and a subsequent buildup of pressure inside the eye. The resulting high pressure compresses the optic nerve and results in pain and in blindness. There are two categories of glaucoma.
Primary glaucoma occurs without any obvious disease in the eye.
Secondary glaucoma occurs when some other cause is present. Another way to categorize glaucoma is based on how the drainage angle appears on examination. The drainage angle may be open, narrowed, closed, or abnormally developed. Primary glaucoma is known to occur in certain purebred breeds of dogs and is thought to be inherited. Breeds in which we see primary open-angle glaucoma are the Beagles, Miniature Poodles and Norwegian Elkhounds.