Glaucoma in dogs and cats also known as glaucoma is a painful condition that results in increased pressure in the eye due to an abnormal drainage of eye chamber fluid. The high pressure can damage the retina and optic nerve and eventually lead to blindness.

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Written by our vet

Glaucoma

On this page, you can read about glaucoma - henceforth called glaucoma, about how it occurs, symptoms and treatment.


Why and how does glaucoma occur?

In a healthy eye, fluid is produced all the time, and this is drained out through the angle of the eye chamber between the iris and the cornea. The fluid brings nutrients into the eye and transports waste materials out of the eye. Normally, there is a fine balance between fluid in and out of the eye. If this balance is shifted, the pressure in the eye changes. In glaucoma, the drainage conditions in the chamber angle are reduced or blocked. Glaucoma can have different forms and is divided into primary and secondary glaucoma. Primary glaucoma occurs at various ages in predisposed breeds and is considered hereditary. Not all predisposed dogs get glaucoma, but if this disease develops, it will affect both eyes, but often at slightly different times. On average it takes 9 months. from glaucoma developing in one eye until it occurs in the other eye.


How do we know that the chamber angle is abnormal?

Gonioscopy is an examination that makes it possible to assess whether the dog has a tendency to develop primary narrow-angle glaucoma, "glaucoma". We check the angle of the eye chamber and assess whether the trabeculae are abnormal. Gonioscopy is performed together with ordinary ophthalmoscopy using local anesthetic and a special lens that is placed on the eye." Some dogs need to be slightly sedated before the examination.

Gonioscopy of dog with a lens on the eye.
Here Atella gets a lens on her eye during the gonioscopy examination - Photo by Hans Jacob Beck

Different forms of glaucoma

Open-angle and narrow-angle glaucoma

Primary glaucoma is divided into open-angle and narrow-angle glaucoma. Breeds that are known to have narrow angles should be examined every 3 years until the age of 7 for eye candles because the angle can worsen with age. All types Basset, English springer spaniel, Flatcoated retriever, Samoyed, Siberian husky, American cocker spaniel, Bouvier de flandres, Leonberger, Bloodhound, Chow Chow, Border Collie, Golden retriever, Glen of Imaal terrier, Long-haired vorstehhund, Shiba, Welsh springer spaniel , Dandy Dinmont Terrier, Dutch Shepherd (Rough Hair), Entlebucher Mountain Dog, Magyar Viszla and Tatra Mountain dog are examples of breeds that may be predisposed. You can find a complete overview at Ecvo.org Dog breeds that are known to have open-angle glaucoma (POAG - primary open-angle glaucoma) can in most cases be genetically tested. You can find an overview of the possibilities at Ecvo.org. Gray and black moose dogs, Basset Hounds and Beagles can have open-angle glaucoma.

Secondary glaucoma

Secondary glaucoma develops when other eye diseases lead to reduced drainage through the angle of the chamber, such as inflammation of the eyeball, during lens detachment, and when fibrin or the vitreous body clogs the drainage, bleeding, pigment growth in the trabeculae (Cairn Terrier) and tumors in the eye. Secondary glaucoma can affect all races. Dogs that are predisposed to primary glaucoma and that develop an eye disease should be checked by eye exams sooner than other dogs because the drainage conditions are already worse and other diseases of the eye increase the risk of developing glaucoma.


Which symptoms are the most common?

In the beginning, you will be able to see that the dog squints a little with the eye and may have increased tear production. The eye becomes red and painful. The pupil increases in size, and the cornea (the shiny layer at the outermost part of the eye) will eventually turn grey. Eventually the dog becomes blind. If the pressure has been high over time, the entire eyeball can become enlarged.


How is glaucoma treated?

Glaucoma is a very painful condition with limited treatment options when the disease first appears. Mapping of predisposed individuals and preventive measures in the breeding work are therefore crucial to maintaining good eye health in breeds where the disease occurs.


Pressure reducing agents

Primary narrow-angle glaucoma always affects both eyes, often at different times. Can be experimentally treated with pressure-lowering agents and kept in check for a period if the pressure is stabilized at an acceptable level < 25mmHg. Eventually, a tolerance to the antihypertensive agent will develop, and then it is no longer possible to control the pressure with medication.

Primary narrow-angle glaucoma therefore often ends with the removal of the affected (diseased) eye when the pressure-lowering agents are no longer effective. And after an average of 9 months, the other eye will also be affected (diseased).

Laser surgery (transscleral photocoagulation)

Laser surgery is performed here at A-Vet. The prerequisite is that the optic papilla is intact. We can laser treat both the diseased eye and use laser as preventive treatment on the "healthy" eye. We use two different handpieces and different strengths when treating a "healthy" and a "sick" eye. The treatment will most likely have to be repeated annually. Since November 2022, we have offered laser treatment (transscleral photocoagulation) and so far have good experiences. In secondary glaucoma, it is important to treat the primary cause in addition to pressure-lowering agents for a period. Laser treatment in glaucoma can be considered as the only pressure-lowering treatment or as a supplement to treatment with drops.


Who can be laser treated?

The aim of the laser treatment is to lower the production of chamber fluid. It is done by laser treating the trabeculae where the production of ventricular fluid takes place. Laser treatment of this area is only possible if the angle is sufficiently open and if the cornea is so clear that the eye vet can see the necessary details. Therefore, eyes that are difficult to access or have a damaged chamber angle, inflammatory changes or cloudy corneas will not be able to be treated. Therefore, it is important that the dog or cat is pre-examined (gonioscoped) by an ophthalmologist before any laser treatment is planned.


How does the laser treatment take place?

After an extended health check with blood tests for a thorough assessment of the patient's health status, an anesthetic injection (indifference injection) is given. The patient is put on oxygen and connected to monitoring equipment. The veterinarian in charge of anesthesia administers initial anesthesia. The type of anesthesia given depends on the patient's state of health. The chamber angle is then laser treated with up to 25 laser points according to our own procedure. The patient can go home after treatment, and there should be no pain associated with the procedure itself. Medicines taken for glaucoma should not be stopped after the treatment, and most often an anti-inflammatory medicine is also dripped for at least 3-7 days afterwards. The time of inspection is determined individually. Any further medication is then also considered.


How good is the treatment?

The effect and duration of the laser treatment is mainly determined by the type of glaucoma and its design. Drop treatment that is supplemented with the use of a laser also has a good effect, and it happens that the medication can be reduced. Laser treatment can be done twice in each eye, three months apart. The laser has properties that allow the treatment to be repeated several times, because overlapping treatment can provide additional effect and not damage the trabecular meshwork. According to our German colleagues with long experience, repeated treatment is usually necessary every year.

Can laser treatment damage the eye?

Laser treatment can sometimes cause further inflammation of the eye. Sometimes there may be an increase in pressure in the eye a few hours after the treatment, but only rarely to an extent that causes worsening of the glaucoma damage that already exists according to our German colleagues. An increase in pressure can largely be avoided by correctly setting the laser and the correct quantity and intensity of the treatment.


Explanations of words

Chamber angle

Chamber angle is the angle formed by the cornea (cornea) at the front and the iris (iris) at the back in the anterior chamber of the eye. The chamber angle should normally be open, so that the aqueous humor can be drained through the trabecular meshwork. In some, the chamber angle may be narrow and predispose to a type of glaucoma called narrow-angle glaucoma.


The target pressure

The target pressure (a pressure level at which the glaucomatous damage is thought not to worsen) is determined by assessing many factors. In general, the pressure should be lowered by 30% after the first treatment. All treatment that leads to a pressure of < 25 mmHg at check-up is satisfactory.


Trabecler-Trabekelwerk

The trabecular meshwork is a specially constructed tissue of fine pores located in the chamber angle of the eye
front part. The aqueous humor is drained through these pores into the bloodstream. The
The most common forms of glaucoma are probably due to narrowing of these pores.

A lady playing with a dog and giving the dog a high five with her paw.