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                    Canine Glaucoma                   

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Glaucoma is when the pressure fluid inside the eyeball is excessively high.  When this occurs the internal structure of the eye is destroyed, rendering the eye blind.  Unfortunately glaucoma is often not detected untill it is too late to save the dog's eyesight.  Early signs include pain in the eye, often indicated by the dog rubbing the eye with his paw, against furniture, or your leg; a dilated pupil: cloudiness of the cornea; an increse in the size of the blood vessels in the white part of the eye or you may notice that one eye seems larger than the other.


What is Glaucoma
Glaucoma

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     What is glaucoma?

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related terms: goniodysgenesis, pigmentary glaucoma

Glaucoma is a leading cause of blindness in dogs. It is the result of increased fluid pressure within the eye (elevated intraocular pressure or IOP).  If the pressure can not be reduced, there will be permanent damage to the retina and optic nerve resulting in visual impairment. Complete blindness can occur within 24 hours if the IOP is extremely elevated or can occur slowly over weeks or months if the the elevation is mild. Glaucoma is usually very painful.

Glaucoma may be primary (inherited) or secondary to a number of eye disorders including luxation of the lens, tumours of the eye, and uveitisglaucomacidd (inflammation of the eye).

Primary/inherited glaucoma causes an elevation of pressure within the eye because of abnormal drainage of fluid through the iridocorneal angle. When the angle at which the iris and cornea join is wide, the glaucoma is classified as open angle. If the base of the iris is pushed forward, the glaucoma is described as narrow angle.  

Goniodysgenesis is characterized by an abnormal sheet of tissue in the angle where drainage normally occurs. This may or may not cause an elevation in IOP and glaucoma.

In pigmentary glaucoma, the obstruction to fluid drainage is caused by an abundance of pigmented cells within the iridocorneal angle and sclera. The increase in IOP is progressive and often results in blindness.

How is glaucoma inherited?
Inherited open angle glaucoma is an autosomal recessive trait in beagles. Narrow angle glaucoma is inherited as an autosomal dominant trait in the Welsh springer spaniel. The mode of inheritance for glaucoma in other breeds has not been identified.

What breeds are affected by glaucoma?
Narrow angle glaucoma is much more common than open angle glaucoma. Both types occur in mixed breed dogs as well as purebreds.

open angle glaucoma: beagle, American cocker spaniel, basset hound, Boston terrier, miniature Schnauzer, Norwegian elkhound

narrow/closed angle glaucoma: Alaskan malamute, American and English cocker spaniel, basset hound, chow chow, dalmatian, Great Dane, wire and smooth fox terrier, toy, miniature, and standard poodle, samoyed, Siberian husky, Welsh springer spaniel

goniodysgenesis: basset hound, Bouvier des Flandres, American and English cocker spaniel, This is also seen in the chihuahua, Dandie Dinmont terrier, Norwegian elkhound, toy and miniature poodle, Siberian husky, wire hair fox terrier.

pigmentary glaucoma: Cairn terrier

For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.

What does glaucoma mean to your dog & you?
Primary open angle glaucoma develops slowly over weeks to months. With closed angle glaucoma, which is much more common, there is usually a sudden, rapid elevation in the pressure within the eye. This affects all the structures in the eye. The effects on the optic nerve and retina cause loss of vision.

Glaucoma is moderately to extremely painful. The eye may be red and your dog may paw at it, or rub his or her head along the carpet. The eye may look cloudy due to swelling of the cornea and your dog will be very sensitive to light.  The affected eye may seem larger, or appear to bulge out, relative to the other eye. Other more general signs of pain include loss of appetite and depression.

Glaucoma is an emergency. Treatment must be started as soon as possible if your dog's sight is to be saved. Irreversible damage to the retina and optic nerve occur within a few hours of significant elevation of the intraocular pressure.

How is glaucoma diagnosed?
Glaucoma is one of the conditions your veterinarian will suspect if your dog has a painful eye. It is diagnosed by measuring the intraocular pressure with a tonometer. This can usually be done with  local anaesthetic drops placed in your dog's eye. To determine the type of glaucoma, gonioscopy is used to measure the iridocorneal angle.

FOR THE VETERINARIAN: Because of the potential for elevated IOP to quickly cause irreversible damage to the visual structures of the eye, the timely diagnosis of glaucoma is very important. IOP should be measured in all red eyes for which the cause is not immediately obvious, and in eyes with unexplained pupillary abnormalities, corneal edema, or visual impairment, particularly if these signs occur in a dog that is of a breed with a predisposition to glaucoma.  (See references below for a good discussion of accurate IOP measurement, as well as therapy).

Although the normal range of  IOP varies (based on tonometer and other factors), generally a measurement of >25 mm Hg indicates glaucoma. An IOP of 50 mm Hg or more can lead to permanent optic nerve and retinal damage within hours if not relieved.

How is glaucoma treated?
Preserving vision in an eye with glaucoma is difficult and requires aggressive medical and surgical therapy. Your veterinarian may choose to provide initial emergency medical therapy and refer you immediately to a larger veterinary centre.

Treatment depends on several factors - the type of glaucoma present, the degree of elevation of IOP, and the extent of visual impairment. Primary open angle glaucoma tends to be slower in onset and may, at least initially, be controlled by medical therapy (drugs) alone. With closed angle glaucoma, which is much more common, there is usually a sudden, rapid elevation in IOP. Ultimately, most forms of glaucoma require surgery.

If vision is present or has just recently been lost, a combination of medical and surgical therapy will be used to try and maintain your dog's sight . Aggressive medical therapy (meaning a combination of anti-glaucoma drugs administered frequently and monitored closely) is used to reduce IOP prior to surgery to prevent further damage to the eye. Some of these drugs will be used as well for additional minor IOP reductions following surgery. The aim of surgery in an eye that is still visual (or potentially visual) is to decrease the production of fluid within the eye, and to improve the drainage from the eye. There are a few different methods that a veterinary ophthalmologist can use to achieve this.

If the eye is irretrievably blind, glaucoma can be treated by removing the globe of the eye (enucleation). This will eliminate the pain for your dog. There are also procedures that can be done that preserve the globe such as placing a prosthesis.

Inherited glaucoma usually occurs in both eyes eventually. Your veterinarian will monitor the pressure in the other eye regularly, and discuss with you recognition of early signs of glaucoma. He or she  may also recommend preventive medication for the unaffected eye.

Breeding advice
Animals of predisposed breeds should be screened for glaucoma before being used for breeding. Affected dogs and their close relatives should not be bred. Unfortunately, glaucoma does not generally become apparent until after breeding age has been reached, usually 3 years of age or greater.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Where to find more information?
Both have good information on diagnosis and therapy, including prophylactic therapy for high risk eyes.
Miller, P.E. 1995. Glaucoma. In J.D. Bonagura and R.W. Kirk (eds.). Kirk's  Current Veterinary Therapy XII Small Animal Practice, p. 1265-1272.  W.B. Saunders Co., Philadelphia
Slatter, D. 1990. Fundamentals of Veterinary Ophthalmology. W. B. Saunders Co., Philadelphia


Copyright © 1998 Canine Inherited Disorders Database. All rights reserved.
This database is funded jointly by the Sir James Dunn Animal Welfare Centre at the Atlantic Veterinary College, University of Prince Edward Island, and the Canadian Veterinary Medical Association.
Permission to reprint is granted  by Alice Crook, DVM Coordinator, Sir James Dunn Animal Welfare Centre
Atlantic Veterinary College University of Prince Edward Island

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GLAUCOMA
Glaucoma is defined as excessive pressure inside the eye. The eye is full of a fluid called the aqueous humor, which is constantly produced and drained away from the eye and supplies nutrition for all interior structures. Glaucoma is caused by a decrease in the amount of fluid that flows out of the eye. It is a serious disease and without proper treatment can result in blindness. Unfortunately, even with aggressive medical and surgical therapy, dogs and cats with glaucoma will often lose their vision. Glaucoma is one of the most frequent causes of blindness in adult dogs.

Types of Glaucoma:
There are two main types of glaucoma, primary and secondary. In primary glaucoma, the cause of the increase in pressure is due to decreased outflow from the drainage angle. It is frequently an inherited problem. Beagles, Basset Hounds, and Cocker Spaniels are especially prone to this type of glaucoma. In secondary glaucoma the pressure is too high because something else is wrong in the eye, such as a lens luxation, bleeding, inflammation, or tumor.
glaucomadiag


Aqueous humor made in the ciliary body flows through the pupil into the anterior chamber. Aqueous then drains into the bloodstream through the iridocorneal angle.
Signs of Glaucoma
 A red (bloodshot) eye
 A painful eye
Lids may be held shut
 Excessive tearing
 Eye may appear cloudy or blue
Sudden blindness
 A dilated (enlarged) pupil that does not respond normally to light
Depression
 Appetite loss
Enlargement of the eye


Treatment:
The treatment chosen (i.e. surgery and/or medical therapy) will be influenced by what the goal of therapy is: to stop pain in a blind eye or to preserve vision. Medical treatment consists of a number of different drugs used in combination. Some are given by mouth and effect the whole body, while others are put directly into the eye and have a local effect. The drugs that work when the problem is first diagnosed may not work forever. Therefore, the intraocular pressure needs to be monitored on a regular basis so that the medication regimen can be altered to fit the needs of the patient. Unfortunately glaucoma cannot be cured, only controlled. When medical treatment fails, surgical therapy can help prolong vision, or eliminate pain.

Medical Therapy:
The following categories of drugs are frequently used:
Carbonic anhydrase inhibitors: Oral and topical formulations reduce the amount of fluid produced inside the eye. (Methazolamide, dorzolamide or Trusopt )

Miotics (Parasympathomimetics): Used on the eye, they help to increase the outflow of fluid from the eye. They may cause a temporary redness, burning or stinging in the eye. (Pilocarpine)

Beta-adrenergic blockers: reduces the amount of fluid produced inside the eye. (Timolol)

*By using very small amounts of several of the drugs, the risks of side effects can be reduced.

*Please keep these drugs out of the reach of children.
Surgical Treatment:
In some cases, surgical procedures are available that may help to provide long-term control. One of these procedures uses a laser to destroy the part of the eye that produces fluid and thereby reduces the pressure. Another surgery inserts a tube into the eye that shunts the fluid under the conjunctiva (pink tissue) deep in the eye socket. Neither surgery is 100% effective and multiple surgeries over several years may be required to preserve vision.

A blind, painful eye can be removed to eliminate discomfort for your pet and to avoid the need for medicines that are expensive and affect the whole body. The surgery to remove the eye is called enucleation. After the eye is removed, the eyelids are permanently sewn shut. This means that the dog will look like he or she is winking at you.

Blind painful eyes may also have an intraocular prosthesis placed after a procedure called evisceration. With this surgery the contents of the eye are removed and silicone prosthesis is placed inside the eye. The outward appearance of the eye is preserved but no longer has the pain from high pressure. Afterwards, the eye looks fairly normal, but remains blind.
EVISCERATION WITH PLACEMENT OF AN INTRASCLERAL PROSTHESIS
 This surgical procedure is a cosmetic alternative to enucleation and is performed on blind and painful eyes. The contents of the eye are removed and a sterile silicone ball (the prosthesis) is placed within the eye. This looks fairly normal, moves normally, remains blind, but is no longer a source of pain. The photographs below show a dog with prostheses in both eyes (the smaller photo is a closer view.)
glaucoma1
glaucoma2
 
Remember:
Each case is different and therapy must be tailored to the individual patient. Intraocular pressure must be measured regularly and the eye should be treated as prescribed. Do not stop any medication unless directed to do so by your veterinarian.
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The above information is simply informational. It's intent is not to replace the advice of a veterinarian nor to assist you in making a diagnosis of your pet. Please consult with your own veterinarian for confirmation of any diagnosis. Your pets life may depend on it.