The fluid inside the eye is called the aqueous humor which is produced in the ciliary body which is located behind the iris. This fluid flows through the pupil and drains from the eye through a sieve-like network located at the junction of the cornea and the iris called the iridocorneal cleft or drainage angle. Glaucoma occurs as a consequence of inadequate outflow of aqueous humor and a subsequent buildup of pressure inside the eye. The resulting high pressure damages the optic nerve and results in blindness. There are two categories of glaucoma.
Primary glaucoma occurs without any other ocular cause.
Secondary glaucoma occurs when some other inciting cause is present. Primary glaucoma is known to occur in certain purebred breeds of dogs and is thought to be inherited. Breeds in which we see open-angle glaucoma are the Beagles and Norwegian Elkhounds. A developmental abnormality of the drainage angle called goniodysgenesis which results in decreased outflow during times of inflammation is seen in the Basset Hound, American and English Cocker Spaniel, Samoyed, and Chow Chow. Secondary glaucoma is the result of some intraocular condition that interferes with the natural flow of ocular fluid.