Glaucoma, when left untreated, will cause permanent damage to the optic nerve and cause blindness in a dog's affected eye. Unfortunately, according to PetMD, 40 percent of dogs with glaucoma will experience blindness within the first year after onset -- whether or not there has been veterinary intervention. Glaucoma can occur at any age, but most dogs with primary glaucoma are diagnosed mid-life.
Average Age of Onset
There are two types of glaucoma. Primary glaucoma most often affects dogs at 3 to 7 years of age. Secondary glaucoma is caused by trauma, cataracts, inflammation or cancer. Both kinds of glaucoma are caused by a buildup of fluid in the eye, and therefore high intraocular pressure. In primary glaucoma, the lack of fluid drainage is because the filtration angle of the eye is too small. This physical attribute is evident most often in purebred canines, according to the North Caroline State University College of Veterinary Medicine.