Vision loss from glaucoma may take a long time in the Norwegian elkhound, chow and Shar Pei breeds. This difference is thought to be related to variations of blood flow pressures within the eyes of different breeds. Secondary glaucoma can occur in any type of dog. The most common cause is related to chronic inflammation within the eye, for which there are many different causes. Terrier breeds commonly suffer from secondary glaucoma because they tend to have an instability of their lens, which causes it to dislocate within the eye, obstructing normal fluid drainage.
Congenital glaucoma is present at birth or occurs shortly thereafter.
Increased fluid pressure develops within the eye during the anatomical development of the drainage system. The signs of early glaucoma can be difficult for pet owners and even veterinarians to recognize, especially if the pressure within the eye is only minimally elevated. Generally, recognition depends upon the aggressiveness of increased eye pressure. For instance, the higher the pressure, the easier it is to suspect a diagnosis of glaucoma. The cornea often shows varying degrees of cloudiness and may look like ground glass.