CANINE GLAUCOMA
By Vickie Halstead, RN, CVNS, CCRN, CEN, LNC
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Diagram from The National Eye Institute
http://www.nei.nih.gov/health/eyediagram/
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:
- A red, exquisitely painful eye with vision loss and increased intraocular pressure
- The affected eye may feel harder than the normal eye
- 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:
- An enlarged, protuberant eye compared to the fellow eye, with increased intraocular pressure
- Signs of chronic pain and vision loss
- The eye may feel tender to pressure and harder than the fellow eye
- 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
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