Glaucoma in dogs is a painful condition caused by increased pressure (intraocular pressure – IOP) inside the eye. To best understand glaucoma in dogs, you really need to know more about your dog’s eye anatomy. Don’t worry. I won’t bore you to tears (pun intended).
There are 3 categories of canine glaucoma including primary, secondary (most common), and congenital. Unlike the type of glaucoma you or I might get, canine glaucoma is much more likely to cause blindness. By the time you’re finished reading this post, you’ll understand why.
Glaucoma in Dogs -- The Ciliary Body
The ciliary body plays an important role because it:• produces the fluid that keeps the shape of the eye (if it didn’t, you’d have a deflated eyeball)
• provides vital nutrients and oxygen through the fluid it produces (known as aqueous humor)
• suspends the eye’s lens in place
In a healthy dog eye, the liquid drains back into the dog’s system through an opening between the cornea and the iris. The ciliary body does its own thing within the eye itself, working hard to maintain a healthy equilibrium.
Still can’t picture it?
Imagine overfilling a water balloon. The balloon is going to get larger and larger, creating pressure and compromising the balloon’s integrity. The same thing happens to the dog’s eye when normal drainage cannot take place.
This strain and pressure within the eye can eventually damage the optic nerve (and ganglion cells), causing blindness. Systemically, it’s thought that the increased intra-ocular pressure causes damage to the optic nerve, which then results in a loss of retinal ganglion cells.
Retinal Ganglion Cells
These cells (neurons) transmit image-forming and non-image forming communication between the retina and the brain. Each ganglion cell receives visual information from photo receptors.
I’m just going to come out and say that I don’t totally understand all of the complicated workings of each ganglion cell. As I mentioned above, I’m not a veterinarian. From what I can gather, however, these cells are an important part of the informational highway to the brain. They manage pupil function and transmit visual information.
Intra-ocular Pressure (IOP)
Both the optic nerve and retinal ganglion cells are damaged by the intra-ocular pressure of glaucoma in dogs. The damage caused typically results in partial or complete blindness.
Normal IOP in Dogs
Normal pressure in dogs ranges between 10 and 20 mmHg (millimeters of mercury). Pressures ranging between 30 and even 50 mmHg has been represented in dogs with glaucoma.
An article written by Paul E. Miller, DVM, and Ellison Bentley, DVM, (published November, 2015, in Veterinary Clinics of North America: Small Animal Practice) reports that damage to the optical nerve or associated tissues can actually begin long before intra-ocular pressure (IOP) increases.
The significance is that glaucoma in dogs isn’t all about pressure damaging the optic nerve. It might be one characteristic of the disease, but it’s not necessarily the whole picture.
Primary and Secondary Glaucoma in Dogs
Primary glaucoma in dogs is thought to be an inherited condition in which fluid does not drain normally. It’s typically seen in specific breeds (listed below) between the ages of 5 and 6 years, or in much older dogs. This type of glaucoma in dogs is usually caused by what’s known as “closed angle” glaucoma; however, (rarely) it can also be caused by open angle glaucoma.
Scroll down further for descriptions of open and closed angle glaucoma.
Acute primary glaucoma can come on suddenly. What that happens, it is considered a medical emergency. If the eye isn’t treated immediately, loss of vision is likely.
Since primary glaucoma is considered genetic, there’s a strong likelihood that both eyes will be affected by the disease. There is no cure for glaucoma in dogs.
Medical treatment involves reducing the pain caused by increased pressure in the eye. It’s also important to follow protocol in maintaining the health of the other eye for as long as possible. More information below.
Primary Closed Angle Glaucoma in Dogs (most common of the primary glaucoma type)
There are a lot of complicated medical terms to describe this process, but – essentially – the drainage angle becomes blocked by the iris. Primary glaucoma is caused by genetic defects that affect the eye. Once the fluid is trapped inside, pressure (inter-ocular pressure or IOP) builds quickly within the eye. Veterinarians refer to this as “acute glaucoma”, which is a medical emergency.
When this happens, there is a very high chance that your dog will go blind in the affected eye.
If you’re up for some serious medical jargon, check out this article at Veterinarian Medical Center of Long Island website.
Primary Open Angle Glaucoma in Dogs (least common)
This type is considered a genetic mutation causing the build-up of pressure within the eye. The condition prevents the fluid (aqueous humor) produced by the ciliary body from draining naturally. As a result, death occurs within the ganglion cells.
As mentioned above, this isn’t particularly common, especially if breeders are carefully selecting dogs based on accurate DNA testing.
As promised, here is a list of dog breeds at risk of genetically acquired glaucoma:
BREED SPECIFIC PRIMARY GLAUCOMA:
Jack Russell Terrier
English Cocker Spaniel
American Cocker Spaniel
English Springer Spaniel
Flat Coated Retrievers
Smooth-haired Fox Terrier
Wire-haired Fox Terrier
Please note that in the list of breeds above, some dogs are more prone to glaucoma than others. It doesn’t mean that every dog in the list will get glaucoma.
You might also be interested in reading Wisdom Dog DNA Tests vs Embark Dog DNA Tests 2018
SECONDARY GLAUCOMA IN DOGS (Most Common)
This particular type of glaucoma works the same way, in that there is increased pressure within the eye. The causes, however, are typically due to disease (cancer, for example) or eye injuries.
This is the medical term for the inflammation of the eye’s interior. Debris and scar tissue end up blocking the drainage angle in this case.
If tumors are present within the eye, they can cause blockage of the drainage angle.
• Dislocation of the Lens
In this situation, the lens actually tips forward and blocks the drainage angle. This is another scenario in which fluid keeps going in, but has no way of getting out.
• Blood Clot
This is known as intra-ocular bleeding in which a blood clot blocks the drainage area.
• Lens Injury
If the dog’s eye is seriously damaged, the lens proteins begin leaking into the eye. This creates an inflammatory condition. The swelling then blocks the drainage angle.
The Difficulty Associated with Early Diagnosis
It can be difficult to notice early signs of glaucoma in dogs. Unless it’s acute, the disease can progress slowly and the symptoms noticed can be passed off as a condition of ageing. Your dog obviously can’t tell you about the pain, and unless he/she actually has a bulging eye or is really rubbing the area, you could easily miss the signs.
Secondary glaucoma in dogs is usually associated with increasing age.
The most common signs of glaucoma in dogs are:
Some dogs do a pretty good job of hiding discomfort and others might begin pawing at the area immediately. If your dog moves his/her head away from you when you try to get close, or appears to be guarding or protecting the face, have it checked out by a licensed veterinarian!
My golden retriever seems to have naturally watery eyes that causes a dark stain on her fur. If there were a problem with her eye, the discharge would increase and become much more obvious. Along with this, your dog might seem “down” or have the blues. Remember, glaucoma in dogs is a painful condition.
Take a second to look into your dog’s eyes. Do the corneas look grey, colorless, or even blue-tinged? If so, get your dog to a veterinarian as soon as possible.
This is going to be pretty noticeable. As the disease advances, you’re going to see one, or both, of your dog’s eyes bulging. It might not be a lot, but you’ll notice a difference.
Other signs include:
- • Blinking a lot.
- • Reddened blood vessels
- • Dilated pupil
- • Pupil that doesn’t respond to light
- • Partial or complete blindness in one eye.
Making the Diagnosis of Glaucoma in Dogs
Veterinarians have a variety of tools used in the diagnosis of glaucoma in dogs.
A tonometer is an instrument that measures pressure within the dog’s eye to determine the presence of glaucoma. This can be done without the use of anesthesia. To do the test, the veterinary ophthalmologist places a device on the eye to measure the amount of pressure.
In this case, a special contact lens-like prism is placed on the eye to evaluate how the internal drainage system is working. In particular, this device is able to see how well the anterior chamber angle is performing.
Of course, the veterinarian will do a simple physical examination as well. This involves looking at the eyes for signs of redness, inflammation, eye discoloration, and a test for vision.
Treatment Options for Glaucoma in Dogs
Here’s where things really get tricky. Once the veterinarian has diagnosed glaucoma (whether primary or secondary), the first thing that needs to be done is to remove pressure ASAP. The quicker pressure is released, the less damage is done to the optic nerve. In addition, the release of pressure reduces pain.
Note: Opening the drain and keeping it open in animals is difficult and costly. Most people opt for medicine that helps reduce the fluid build-up.
Surgical removal of the eye (called enucleation) is typically reserved for end-stage glaucoma where blindness has occurred or is imminent.
There are several treatment options. The problem is the expense, commitment to lifelong treatment, and the fact that eventually, even the good eye will succumb. Eventual blindness is almost guaranteed.
Treatment options include:
- medicated eye drops
- stress management
- change to using a harness rather than a neck collar
- surgery to remove the eye
Medicated Eye Drops
Glaucoma eye drops and pills are expensive and are usually used to preserve sight in the unaffected eye for as long as possible. They are also used temporarily in dogs waiting for surgery.
Complementary and Alternative Medicine
This involves using lifetime therapies using canine antioxidant vision supplements. There are a variety of available supplements (ask your veterinarian for a recommendation). These supplements typically contain:
• amino acids
• Omega 3 fatty acids
• and other combinations of antioxidants
If the dog has gone completely blind in that eye, you still have a few options. Some people prefer to have the eye removed and the area stitched. It’s important to understand that regardless of whether the dog has vision or not, that eye is still going to cause pressure and intense pain.
Other Medical Treatment Options include:
-artificial lens and a drainage device
-insert an implant into the eye socket then stitch the lids shut. This helps to maintain the shape of the eye socket so that the dog doesn’t wind up with a sunken look.
-injection of a drug into the eye socket. This drug is designed to kill the fluid-producing cells. Doing this helps to keep the overall pressure down which would reduce the dog’s pain.
-Laser surgery is done only when the surgeon believes there is a reasonably strong chance that the dog will have vision in that eye for a while.
-remove the eye and replace with a black ball that serves as a device to keep the eye socket in shape and remove the chance of a sunken in appearance later on.
-The blind eye is replaced with a colorless ball that makes it look as if the dog still has a working eye.
REMEMBER: You can’t leave the blind eye in the socket because the pressure is still going to be there. That pressure causes significant pain.
Glaucoma in dogs is a long-term, painful, and expensive condition. As long as the dog lives, he/she will require antioxidant vision supplements to slow down the progress of the other eye, frequent intra-ocular pressure measurements, and topical or oral medications to help lower fluid production.
Types of Medication Used for Glaucoma in Dogs
These drugs work by drawing fluid from the eye.
Beta Blockers help by reducing blood pressure.
• Carbonic Anhydrase Inhibitors
This class of drug works by decreased the production of fluid from the ciliary body. If you’ll remember from earlier, this fluid is called aqueous humor.
Cholinergics (Miotics) work by reducing eye pressure. To do this, the drug supports increased drainage of intraocular fluid.
This eye drop is used for open angled glaucoma and works by increased the outflow of fluid from the eye.
SURGERY – When blindness is inevitable
When or if your dog loses his/her sight, you will have even bigger decisions to make.
This type of surgery generally utilizes a laser to reduce the production of aqueous humor. Unfortunately, this type of surgery (because it is non-invasive) isn’t able to determine exactly how much the ciliary body has been destroyed. A lens implant is usually required post-surgery in order to prevent cataracts from forming later on.
Surgery to Increase Aqueous Humor Outflow
Shunts can be used through an implant and tubing that permits the fluid to drain effectively from the anterior chamber. This is a difficult procedure not proven to affect a positive long-term outcome. There are several possible complications associated with this surgery as well.
Depending on financial status and the type of aesthetic outcome desired, people generally choose this option because of it is effective and much less expensive. Essentially, this involves removing the eyeball. A prosthesis can be inserted to improve the appearance and, by removing the eye, your dog is relieved of pain.
A silicon ball is inserted within the eye resulting in a better appearance and few complications. It’s thought to have a 95% success rate.
An injection of gentamicin (antibiotic) and dexamethasone (corticosteroid) is inserted directly into the ciliary body. Complications could include eye inflammation and retinal detachment.
When It’s NOT Canine Glaucoma
• Nuclear Sclerosis
Nuclear sclerosis is a common condition in ageing dogs that does not affect vision and does not require treatment. It’s different from cataracts. Cataracts occur behind the lens and block the veterinarian’s view of the retina.
The bottom line is that if you notice redness and some discoloration in your dog’s eyes, it doesn’t necessarily mean he/she has glaucoma. Glaucoma is very painful, can come on very quickly (acute) in which case it is imperative to seek veterinarian attention. He/she will want to reduce that fluid build-up ASAP.
Under normal circumstances, your dog’s eyes can become irritated or infected from any number of things. In most of these cases, medicated drops work well. Mild infections and irritations are not going to threaten your dog’s vision. In rare cases where you totally ignore what’s happening and the infection gets worse…you’ll have a problem. But who does that?
Dogs DO Adjust to Vision Loss
People are surprised to learn that dogs bounce back very quickly. Partial or even total blindness can be overcome with a little patience and preparation around the house.
-Enable sound cues
-lots of talk direction
-create awareness so that other people treat the dog accordingly
-close off any danger zones (for example, stairs with baby gate)
DID YOU KNOW? Dogs have about 300 million scent receptors compared to our 6 million?
MYTH: Blindness does not cause other senses to become heightened. The disabled dog (or person) has to rely on the other senses for survival and, therefore, pay particular attention to those senses more. It doesn’t mean that they have become heightened in any way.
While glaucoma in dogs isn’t life-threatening, it can cause pain and serious damage if not treated. As our dogs age, our responsibility to bring them for regular veterinarian check-ups increase. The faster glaucoma is found and treated, the better. At the end of the day, I think we all want the same things for our dogs: The best life we can give them.
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