Canine glaucoma can be divided into primary and secondary forms. It is important to recognize primary glaucoma because it is, by definition, ultimately bilateral and the normal fellow eye is at risk. Primary glaucoma is due to an inherited defect of iridocorneal angle or trabecular meshwork that eventually impairs aqueous outflow. Primary glaucoma is diagnosed when IOP (inter-occular pressure) is elevated in the absence of signs of concurrent ocular disease. Secondary glaucoma is usually an unilateral disease and is associated with a concurrent disease such as inflammation, neoplasia or hemorrhage which decrease or stop aqueous outflow. Glaucoma also often occurs in association with luxation or subluxation of the lens.

In most cases the diagnosis of glaucoma in dogs is not complicated. Normal canine IOP is 15 to 25 mm Hg with less then 5 mm Hg difference between the eyes, so IOP that is over 30 mm Hg is pathologic. Mostly to measure the intraocular pressure we use Schitz tonometer or electronic tonopen, which is easier to use but much more expensive. After establishing diagnosis of glaucoma with objective tonometric measurements, one must determine the vision potential of the affected eye before appropriate therapy can be employed.

Choosing a proper therapy depends on a proper thorough diagnostic evaluation. What may be appropriate for the sighted eye is often entirely inappropriate for the blind painful eye. For the sighted or potentially sighted eye acutely affected by glaucoma, the goal of therapy is to maintain vision and comfort as long as possible using any or all appropriate medical or surgical therapy. When the eye becomes irreversibly blind, the goal of therapy changes. The most important thing the clinician can do for the blind glaucomatous eye is to reduce the pain and make it comfortable.