Canine Glaucoma

Etiology

Glaucoma is one of the most common causes of blindness in dogs. Although bichons are not listed as one of the breeds predisposed to glaucoma, several cases were sited in our health survey a few years ago and in the internet data retrieved from the health information site on BFCA’s web site www.bichon.org. Primary glaucoma is inherited in most cases in either autosomal recessive or autosomal dominant traits. Secondary glaucoma results from eye disorders such as lens luxation (displaced), eye tumors, inflammation of the eye, or eye trauma.

Pathophysiology

Glaucoma is defined as an elevation of pressure inside the eye to the point that it produces structural changes that lead to blindness. The excess pressure damages the retina and optic nerve. The retina receives light stimuli from the environment and converts it to an electric signal that is sent to the brain via the optic nerve, which lies behind the retina. The brain interprets this signal and vision occurs. Normally there is a constant flow of the fluid produced inside the eye, through a filter located near the cornea, and then out to the systemic circulation. Glaucoma occurs when there is an abnormality in the filter that obstructs the drainage of this fluid. Primary glaucoma occurs in both eyes, but the rate of progression of the disease may differ between fellow eyes.

Signs And Symptoms

Blindness resulting from glaucoma is much more common in dogs than humans, being that dogs cannot communicate the early signs such as blurred vision or headaches. By the time the owner notices the symptoms and seeks medical attention, the disease is so advanced that it may be too late to save the dog’s sight. The most common sign is a red, painful eye exhibited by squinting, tearing, rubbing the eye, loss of appetite, and a decrease in activity. Glaucoma can present in the acute or chronic stage, both of which are evidenced by elevated intraocular pressure (the pressure inside the eyeball) and visual loss. The intraocular pressure can be measured by an instrument called a tanometer which many veterinarians, and of course ophthalmologists, possess.

Acute glaucoma is a medical emergency. Irreversible damage to the optic nerve and retina can occur within a few hours. The signs of acute glaucoma include:

1. A red, exquisitely painful eye with vision loss and increased intraocular pressure
2. The affected eye may feel harder than the normal eye
3. A swollen, cloudy cornea (the normally transparent structure covering the colored portion of the eye) with a dilated pupil

Some forms of glaucoma progress more slowly, allowing the clinical signs to be less obvious, and therefore detection may be delayed until the disease progresses to end stage. The signs of end stage, chronic glaucoma include:

1. An enlarged, protuberant eye compared to the fellow eye, with increased intraocular pressure
2. Signs of chronic pain and vision loss
3. The eye may feel tender to pressure and harder than the fellow eye
4. Ophthalmology exam would detect changes in the optic nerve and retina

Management

The two major therapeutic goals in managing a dog with glaucoma are to control the pain and to preserve or restore the vision. Medical therapy, which is often not successful because it is too late to restore vision, includes eye drops and oral medications to reduce the amount of fluid produced in the eye and to restore flow through the filter. If the eye remains visual, surgical procedures can be performed by an ophthalmologist. If the eye is irretrievably blind, the globe of the eye can be removed to eliminate the pain, followed by suturing the eyelid closed or placing a prosthesis. Ultimately, inherited glaucoma will develop in both eyes. If a dog has lost the vision in one eye due to glaucoma, a very important therapeutic goal is to maintain vision in the other eye. This would involve frequent eye exams and prophylactic medications. If your bichon exhibits signs of glaucoma, immediately seek the services of an ophthalmologist, or at least a veterinarian who possesses a tanometer to measure the intraocular pressure.

Breeding Advice

As responsible bichon frise breeders, we must be aware of glaucoma and stop the progression of this disease in our breed while the incidence is low. We can accomplish this by being able to recognize the signs of glaucoma in our bichons and not breeding bichons with primary glaucoma, or their close relatives. Unfortunately the age of onset is 3 years or more, after breeding age has arrived. Predisposed breeds should be screened for glaucoma during the annual CERF exam with an additional test, which is not necessary at this time for bichons unless glaucoma has been detected in your line. The CERF exam could inadvertently detect early stages of chronic glaucoma, evidenced by changes in the retina or optic nerve.

Since the Health and Education Committee feels that this disease deserves vigilance, we will keep you informed on recommendations for glaucoma screening. We also encourage you to share data with our committee, which will remain confidential, so that we can be aware of current trends in health problems in bichons.

Research for this article includes:
The Merck Veterinary Manual
The 5 Minute Veterinary Consult by Larry Tilley& Francis Smith
The Dog Owner’s Home Veterinary Handbook by James Griffen & Liisa Carlson