Glaucoma is a leading cause of blindness in humans and canines. While it is incurable, it can be treated and controlled. Because the disease progresses slowly, symptoms do not present at onset and there are often no warning signs to indicate that a problem — increased eye pressure — is present. Therefore, it is critical to monitor every companion animal’s eyes for visible and behavioral abnormalities. Contact your veterinarian immediately if you detect any changes or have concerns about your companion's health.
Dr. Doug Esson of Eye Care for Animals is a veterinary specialist in the diagnosis and treatment of canine glaucoma. In this interview, he discusses the symptoms, causes and treatments for this eye disease.
What are the differences between primary and secondary glaucoma, and how common is each eye disease in canines?
Primary glaucoma refers to a group of diseases associated with inherited abnormalities in the structure and function of the eye, which result in the development of excessive intraocular pressure, typically as the animal ages. Secondary glaucoma refers to pressure-associated problems within the eye as a result of acquired structural or functional problems such as trauma, chronic inflammation associated with cataracts or the development of a tumor inside the eye. The canine glaucomas occur at approximately the same frequency as do the human glaucomas, divided roughly equally between primary and secondary causes.
Are certain breeds more susceptible to glaucoma than others?
Certain breeds are recognized to be at increased risk for the development of primary (hereditary) glaucoma. These include the Cocker Spaniel, Bassett Hound, Chow Chow, Shar Pei and Siberian Husky. Any breed, or mixed breed, may develop secondary glaucoma.
As in humans, primary glaucoma is more common and presents as open angle and closed angle. How do these differ, and again, how common are these diseases?
The frequency of incidence of the primary and secondary glaucomas is roughly equal in dogs. The term "open angle glaucoma" describes glaucoma in the presence of an ocular drainage system ("angle") with a normal appearance, despite metabolic abnormalities within its structure. The term "closed angle glaucoma" describes glaucoma in association with visible structural abnormalities in the drainage system of the eye. Having an abnormal (or "goniodysgenic") drainage system does not necessarily imply that a dog will develop glaucoma.
What are some of the causes of primary and secondary glaucoma?
The mechanism of primary open-angle glaucoma is likely associated with an accumulation of abnormal proteins within the drainage system of the eye. The mechanism of primary closed-angle glaucoma is likely represented by the degeneration and remodeling of tissues with the drainage system of the eye, to a point where sudden and complete obstruction of fluid flow within the eye occurs, resulting in collapse of the tissues surrounding the drainage system and a subsequent sudden and dramatic increase in pressure within the eye. Secondary glaucoma generally results from post-inflammatory alterations to the drainage system of the eye, such as the accumulation of blood, inflammatory debris, neoplastic cells or scar tissue.
What are the symptoms of each? Are there non-vision-related symptoms as well?
The primary open-angle glaucomas typically present in a more gradual manner over months or even years, whereas the majority of cases of primary closed-angle glaucoma present as acute events, usually within just a few hours. In both cases, however, the changes underlying these events probably take months or years to develop. The secondary glaucomas may develop across a variable timeframe, depending on their cause. Changes which an owner may notice include increased redness of the eye, a clouding of the cornea as a result of fluid accumulation within the tissues, vision decrease or loss, and signs of discomfort or pain such as squinting, elevation of the third eyelid, lethargy and inappetence.
At what age does glaucoma usually present? Because primary glaucoma is sometimes hereditary, is it present in puppies?
A distinction should be made between the terms "congenital" and "hereditary.” Congenital implies something that was present at the time of birth. This type of hereditary glaucoma is devastating, but thankfully relatively uncommon. The primary (hereditary) glaucomas occur with a high frequency between 6 and 7 years of age in most affected breeds. An important factor to consider is the likelihood that once a dog has developed primary glaucoma in one eye, it is at high risk for the development of a similar situation in the other eye, often within a six- to 12-month timeframe.
Some breeds have natural discharge from their eyes. What should guardians look for as a symptom of change or concern?
Glaucomatous changes can be difficult to detect clinically; a definitive diagnosis requires that the pressure inside the eye be estimated with specialized equipment. Animals at risk for the development of glaucoma should be serially evaluated by a board-certified veterinary ophthalmologist, so that accurate decisions regarding treatment strategies can be made.
In humans, glaucoma can be present for years before the patient becomes aware. We are told to have routine eye pressure screenings. What about dogs? How often should their eyes be examined and how detailed an exam can be performed? What does this exam entail?
The likelihood that canine glaucoma will be detected in its early stages via routine intraocular pressure testing is low. Serial evaluation of the eye and its structure will, however, allow a veterinary ophthalmologist to develop an optimal treatment plan for each patient as well as provide guidance regarding emergency management. Evaluation of eyes considered to be at risk for the development of glaucoma is subtle and highly specialized, sometimes involving additional diagnostic testing such as gonioscopy, high-resolution ultrasonography and provocative testing, and can only be accurately performed by a qualified veterinary ophthalmologist.
Glaucoma is treatable but incurable. What does treatment involve for dogs and how does it vary depending upon progression of the disease?
Treatment of the canine glaucomas encompasses both medical and surgical approaches. The appropriateness and timing of each should be determined by a veterinary ophthalmologist on an individual case basis.
Do the medications bring risk of side effects? What should be taken into consideration, depending on the age of the dog?
Significant side effects associated with the use of prescription glaucoma medications are generally uncommon. Again, the appropriateness of each product for a given clinical situation should be determined by a veterinary ophthalmologist.
At what point is surgery recommended, what are the surgical options, and in which cases is it not advised?
Surgical options for the treatment of the canine glaucomas encompass the reduction of fluid production inside the eye, typically utilizing highly accurate surgical lasers, and/or the improvement of fluid drainage out of the eye, typically utilizing implantable drainage devices which may be valved or non-valved. These procedures are frequently performed in combination. In many cases, concurrent lens extraction is also advocated. The timing of surgical intervention should be determined by a veterinary ophthalmologist; however, cases in which surgical intervention is delayed excessively may reach a point from which visual recovery is no longer possible.
What are some tips for guardians of dogs who have glaucoma and/or dogs who have lost their vision? What can guardians do to make life more comfortable and manageable for their companions?
In cases where vision is irreversibly lost to glaucoma, eyes can be made comfortable using a variety of medical and surgical approaches, the decision often being influenced by cosmesis.
Learn more about Eye Care for Animals at www.eyecareforanimals.com
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