Glaucoma is not a single disease entity, but a group of ocular diseases which are characterized by progressive death of retinal ganglion cells (the axons of which coalesce to become the optic nerve) and have the common, constant risk factor of elevated intraocular pressure (IOP). It is, unfortunately, an all too common condition in dogs with a prevalence similar to that occurring in human beings (close to 2% of both the human and canine populations). Because there are so many different forms of glaucoma, even beyond the simplistic categories of primary, secondary, congenital, open-angle, and narrow angle, treatment necessarily must target the risk factor that is common to all types. Therefore, the elevation in IOP, which is incompatible with the health of the eye and the maintenance of vision, becomes the factor we rely upon for diagnosis, treatment, and monitoring of glaucoma.