It's true, in dogs glaucoma seems to progress very fast compared to humans.
Indeed, many dog owners are often shocked when they learn that their dog is going blind as a result of glaucoma.
In humans, glaucoma is known for progressing slowly, with just a low percentage of being becoming blind, so what's going on with dogs?
Let's discover more about why glaucoma in dogs progresses so fast.
What Causes Glaucoma in Dogs and Humans?
Glaucoma is a progressive, degenerative eye condition that takes place when there is an increase in intraocular pressure (pressure within the eye).
Why does this pressure inside the eye increase? To better understand the exact dynamics, it helps gaining a deeper understanding on how the eyes work.
In a normal eye, special fluids ensure that the eye is nourished and maintains its typical shape.
In order for these fluids to work well, they should be produced and drained efficiently.
However, sometimes things may go wrong.
When the eyes are healthy, they produce fluids (aqueous humor) that nourish the lens and cornea and help maintain ideal intraocular pressure levels.
These fluids are constantly drained to prevent them from building up.
In the case of glaucoma, these fluids don't drain as they should, and therefore, they tend to accumulate, causing increased pressure within the eye.
This pressure overtime ends up potentially damaging the optic nerve which can ultimately lead to blindness.
The Most Common Glaucoma in Humans
The most common type of glaucoma seen in humans is what's known as primary open angle glaucoma (POAG).
In this type of glaucoma, there is a problem in the drainage of fluids through the trabecular meshwork, due to some type of clog.
Fortunately, the clog is not a majorly deleterious one, which allows a certain level of drainage to happen although the fluids may exit rather slowly. This allows the glaucoma to progress gradually.
The Most Common Glaucoma in Dogs
In dogs, instead, the most common type of glaucoma is primary closed angle glaucoma (PACG).
In this form of glaucoma the drainage angle of the trabecular meshwork is severely obstructed due to smaller drainage holes, explains board-certified veterinary ophthalmologist Dr. Noelle La Croix from the Veterinary Medical Center of Long Island.
This defect in the drainage system is commonly found in American cocker spaniels, bassett hounds, chow chows, English cocker spaniels, miniature and toy poodles, great Danes, flat-coated retrievers, chow chows, Chinese sharpei, Welsh springer spaniels, and bouvier des Flandre and Siberian huskies.
Problems generally start to arise and dogs get older , generally between 5 and 6 years of age.
Females are predisposed potentially due to anatomical features of having a significantly smaller angle opening distance compared to male dogs.
This form of glaucoma often presents in acute form, when there is a sudden entrapment of aqueous fluid leading to rapidly increasing intraocular pressures.
As the pressure increases, the dog experiences severe pain, possibly nausea and vomiting and damage to the point of blindness within hours to months despite aggressive treatment.
Usually, one eye is affected affected first with the other eye being affected days, weeks, or months later.
Stressful events may precipitate the situation such as being groomed or kenneled, moving to a new home, or the arrival of a new baby.
In dogs therefore, glaucoma is a medical emergency where quick intervention is needed to prevent damage.
Other Forms of Glaucoma in Dogs
On top of closed angle glaucoma, dogs may also develop secondary glaucoma and congenital glaucoma.
Congenital glaucoma tends to develop if the puppy's first few months of life.
Secondary glaucoma, on the other hands, occurs as a consequence of some other concurrent eye condition, such as uveitis, cancer, lens luxation, and trauma.
Discover more about secondary glaucoma in dogs.
Few Cases of Open Angle Glaucoma in Dogs
Although not as common as primary closed angle glaucoma, some dogs may also develop open angle glaucoma.
Open angle glaucoma can be found in beagles, Norwegian elkhounds, and some other dog breeds.
As in humans, this type of glaucoma progresses very slowly, over the course of months and years.
Did you know? Because this type of glaucoma closely shares several key elements with the most common human type, dogs with this form have been used as a model for studying human glaucoma for more than four decades.
- Park, S.A., Sledge, D., Monahan, C. et al. Primary angle-closure glaucoma with goniodysgenesis in a Beagle dog. BMC Vet Res 15, 75 (2019)
- Tsai S, Bentley E, Miller PE, et al. Gender differences in iridocorneal angle morphology: a potential explanation for the female predisposition to primary angle closure glaucoma in dogs. Vet Ophthalmol. 2012
- Miller PE, Bentley E. Clinical Signs and Diagnosis of the Canine Primary Glaucomas. Vet Clin North Am Small Anim Pract. 2015 Nov