Canine Glaucoma Basics
A. Giuliano, DVM, MS
Diplomate, American College of Veterinary Ophthalmologists
Assistant Professor, University of Missouri, College of Veterinary Medicine
Glaucoma is defined as an increase in pressure within the eye. The increased pressure is the result of a buildup of the intraocular fluid which is known as aqueous humor. In a healthy animal, aqueous humor primarily drains out through a circular filter at the junction of the clear cornea and white sclera, called the iridocorneal angle. Animals with glaucoma have an abnormality in the filter which obstructs outflow, resulting in a buildup of fluid within the eye. An analogy would be a kitchen sink - if the drain is open and the water is running, the sink is operating normally. However, the drain becomes clogged for some reason and the water continues to flow, then the sink fills up with water and overflows!
There are various causes of a defective filter. Dogs of some breeds are often born with abnormal filters and are therefore prone to getting inherited (genetic or primary) glaucoma in both eyes. Other breeds have a genetic predisposition to developing displaced (luxated) lenses, which block the filters, obstructing the flow of fluid. In both dogs and cats, the filters can be clogged with inflammatory cells if inflammation inside the eye (uveitis) occurs. Intraocular tumors can also lead to glaucoma.
The result of uncontrolled glaucoma is blindness. The increased pressure which occurs in glaucoma quickly destroys the retina and optic nerve, which are essential for vision. If the pressure is not relieved the eye may stretch and enlarge. In order to maintain vision, eyes with glaucoma must be treated early (usually within hours of detecting an ocular problem, as evidenced by an increase in squinting, tearing, rubbing, or redness), before damage to the retina and optic nerve occur and the eye enlarges. The first priority in treating animals with glaucoma is to preserve vision. If a pet has lost vision, the next goal is to keep the pet comfortable.
Treatment for glaucoma: In early cases of glaucoma medical therapy is often instituted. The various medications work, primarily, in two different ways - to decrease production of aqueous humor and to open up the filter to make it more efficient. A pet may be prescribed a variety of topical and oral medications which work in concert to decrease intraocular pressure.
Some cases of glaucoma are resistant to the effects of medications. Surgical treatment of glaucoma may include laser therapy or cryosurgery to reduce aqueous humor production. When vision and comfort are no longer able to be maintained , additional surgical procedures may be recommended including either removal of the entire eye (enucleation) or removal of the ocular contents (evisceration) and placement of a prosthesis (false eye).
In animals that have lost vision in one eye due to primary glaucoma, an important therapeutic goal is to maintain vision in the pet's other eye. Life-long prophylactic glaucoma therapy for the remaining functional eye may be instituted.
Please contact your local veterinarian or board-certified ophthalmologist immediately if you notice any redness, pain, excessive tearing or cloudiness in your pet's eye(s). The earlier glaucoma can be diagnosed and treatment instituted, the better the chances are of maintaining vision in a glaucomatous eye.