Glaucoma in dogs is a serious eye condition which can cause vision loss in dogs. Without treatment the risk of blindness is high.
Glaucoma in dogs is more common in some breeds than others. But as well as a genetic trait for glaucoma, trauma to the eye or inflammation can also cause this condition. Always be alert for signs of glaucoma and see a veterinarian urgently if you become concerned.
Ideally, prevention is better than cure. This means screening at-risk breeds for genetic markers and only breeding from parent dogs that carry a low risk. Read on to learn more about Glaucoma in dogs!
What is Glaucoma in Dogs?
Glaucoma in dogs is an umbrella term for increased pressure within the eye. The causes of that increased pressure can be different, in the same way, that sneezing happens for different reasons (such as sniffing pepper, an allergy, or a cold.)
But glaucoma cases all have something in common, which is there is too much ‘intraocular pressure’ within the eye. This physically stretches the eye and is very painful. Over time, the raised pressure damages the retina and optic nerve. Without treatment, this causes cell death and blindness.
It’s most often the case that one eye is affected initially. But if the dog belongs to a predisposed breed, such as the Bassett hound or cocker spaniels, then it’s likely the other eye will eventually also develop glaucoma. For this reason, a specialist vet, such as a veterinary ophthalmologist, may advise treating both eyes, even though only one is affected.
Anatomy 101: Why the Pressure Behind Eye’s are Important
Think of an eye like a car tyre. A smooth ride only happens because the pressure within the tyre is just right. Not enough air, the tyre is flat and the vehicle runs on the wheel rim. Too much air and the wheel makes poor contact with the road or may even explode.
The eye itself consists of a sphere of connective tissue (albeit very clever, transparent tissue) which is kept in shape by being filled with a special fluid. That special fluid, known as aqueous humor, is produced by cells lining the back (or posterior chamber) of the eye.
The aqueous humor keeps the eye inflated and allows light to pass through to the image sensitive retina. It’s important the eye is correctly inflated or the dog’s vision will be distorted.
Aqueous humor production happens all the time, but this leaves the eye with something of a problem. Like a faucet dripping into a plugged sink, eventually, enough fluid is present to cause a problem.
To avoid this, the eye has a natural drainage system. This means fluid produced at the back of the eye circulates forward into the anterior chamber, where it drains away via the plughole of the uveoscleral outflow.
Problems such as glaucoma happen when fluid is produced more quickly than it drains away. The net gain of fluid increases the pressure within the eye, leading to glaucoma.
There are Two Types of Glaucoma in Dogs!
Two forms of glaucoma exist. Primary glaucoma is the result of a genetic trait that causes poor aqueous humor drainage. Thus, the product of aqueous humor is normal but it can’t drain away. Think of this like blowing more and more air into a car tyre or a balloon.
The breeds most at risk of primary open-angle glaucoma include:
- Bassett Hounds
- Cockers spaniels
- Great Danes
- Springer spaniels
- Border collies
- Golden retrievers
- Hungarian vislas
- Shiba Inu
- Welsh terrier
The second form of glaucoma is called secondary glaucoma. This results from a physical problem which then blocks the drainage of fluid from the eye. In our analogies, this is faucet running into a sink with a blocked drain, causing it to overflow.
There are many causes of secondary glaucoma. These include:
- Bleeding within the eye
- A prolapsed lens
- Inflammation within the eye, often as a result of infection or trauma
- A tumor within the eye
What Causes High Eye Pressure? Causes of Glaucoma
Ultimately, glaucoma is caused by the drain within the eye not working efficiently. To complicate things further, there are two different forms of primary glaucoma. These the primary open-angle glaucoma, where the drainage system is anatomically normal but something ‘fails’ within the eye such as the lens moving out of place.
The other form, primary closed-angle glaucoma, results from the drain or iridocorneal angle is too shallow, which means fluid builds up within the eye.
The causes of secondary glaucoma include anything that causes the drainage angle to become blocked. This is the dog that has a traffic accident with trauma to the head, causing structures within the eye to swell. It can also be the dog that develops a mature cataract, causing the lens to shift out of place and block the drain.
Symptoms of Cloudy Eyes in Dogs
Signs of glaucoma in dogs include one eye appearing larger than the other. The cornea is often bright red, or else the stretched globe gives the eye a milky or opaque appearance.
Glaucoma is painful so the dog may seem depressed, lacking in energy, or even aggressive due to discomfort. They may also lose interest in food, and sometimes hide away from the light.
If you are suspicious your dog has glaucoma the see a vet urgently.
Diagnostics! Is there a Dog Eye Pressure Test?
Diagnosing glaucoma requires the veterinarian to measure the pressure within the eye. This is done with a device called a tonometer. This is a non-painful test, much like the puff of air against your own cornea when you have an eye test of the optometrist.
This test can be done with sedation, although the vet may first drop some local anesthetic into the eye to dull any peculiar sensations. The vet takes several readings for both eyes and then takes an average figure for each one.
The vet also examines the anatomy of the eye using an ophthalmoscope. Specifically, this looks at the drainage angle, checks for abnormal tissue such as a tumor, and for inflammation.
So, How do Vets Treat High Eye Pressure Problems?
Glaucoma can come on very suddenly (acute glaucoma) or more gradually (chronic glaucoma).
The sudden form requires more aggressive treatment, which can include intravenous drugs. The latter help reduce the pressure in the eye by drawing fluid out.
However, most chronic forms of glaucoma are managed using eye drops. Different medications exist that work in varying ways. It’s not unusual for the vet to prescribe several different types of eye drop, for maximum benefit to the dog.
Typical medications work by:
- Opening up the drainage angle in the eye, allowing fluid to flow away more easily
- Decrease the production of an aqueous fluid with carbonic anhydrase inhibitors
- Antiinflammatory drugs to reduce swelling of the drainage angle.
In addition, the vet may prescribe pain-killing medications, since glaucoma can be a painful condition, especially in the acute form.
If a particular problem is present, such as an anterior lens luxation, then surgery may be required. Much like unblocking that kitchen sink, when the lens is removed this allows the eye to work normally again.
Some of the hereditary causes of glaucoma can respond well to surgery. For example, placing a small stent or drain through the cornea allows aqueous humor another way to escape from the eye.
Can Dog Glaucoma be Prevented?
Sadly, there is no magic bullet to prevent glaucoma from developing. In high-risk breeds, an intrascleral prosthesis may provide extra drainage. However, these fine stents or tubes are prone to blocking, and so even then may not provide an answer.
If one eye has developed glaucoma and the dog belongs to an at-risk breed, then the vet may be pro-active about the second eye. They may prescribe medication ahead of the ‘good’ eye developing glaucoma to try and delay the inevitable. However, even this may not be enough to keep the eye healthy.
Embark DNA Testing!
Responsible breeders of dogs at risk of primary glaucoma screen their parent dogs for glaucoma. By identifying those dogs that carry the glaucoma gene, the breeder can avoid using that dog for breeding. Hence, by selecting dogs with a low risk of developing glaucoma to produce the next generation of puppies, future misery can be avoided.
However, it should be pointed out that DNA tests are all about probability and predicting those dogs most likely to develop glaucoma. The important difference is that having the glaucoma gene doesn’ t automatically mean they are guaranteed to get glaucoma but that they are at higher risk than other dogs.
Screening for the glaucoma gene is super-easy with Embark DNA testing. All it requires is for you to swab the dog’s cheek with a special applicator. This sample is then sent by post to Embark’s laboratories where it is processed. The results are compared against an extensive database, both of dog breeds and genetic health conditions.
You then receive a full report into the dog’s heritage and genetic predispositions to disease.
The Outlook for Canine Glaucoma
Sadly, glaucoma is not a rare condition. Controlling the raised pressure takes considerable commitment and cost. Even then the results can be disappointing.
Since glaucoma is a painful condition it may be humane to enucleate (surgically remove) the eye. This is especially justified after retinal detachment or permanent blindness has occurred. The use of drugs is then manly to relieve pressure and reduce pain, but the dog is permanently blind.