Glaucoma In Dogs: Causes, Symptoms, And Treatment

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Glaucoma in dogs (i.e. high pressure within the eye) can be a painful and sight-stealing condition. Integrative veterinarian Dr. Julie Buzby explains the causes, symptoms, diagnosis, and treatment of glaucoma to help devoted dog parents feel more prepared should their dog develop glaucoma.

Your dog’s eyes are so much more than just the windows to his or her soul. Compared to humans, our canine companions have a more discerning sense of vision. Plus, they rely on their sight for all manner of day-to-day activities.

So, think about this: What would happen if your furry best friend’s sight was suddenly impaired? It is important to know that some of the diseases that can impact the eye, especially glaucoma, may not only be painful but also ultimately cause blindness.

What is glaucoma in dogs?

You may have heard of glaucoma in people, but it turns out that it can impact dogs too. Glaucoma is a medical condition that causes increased pressure within the eye (i.e. intraocular pressure or IOP). It may affect one or both eyes in dogs.

Unfortunately, glaucoma can cause severe damage to the affected eye. If nerve signals and/or blood flow to the eye’s internal structures are compromised, it can result in permanent blindness due to death of the cells that compose the retina.

To understand glaucoma in dogs, let’s first look at the anatomy of the eye.

Eye anatomy

The eye is composed of many delicate structures which work together to allow the eye to remain healthy and function correctly. Let’s define some relevant eye anatomy terms:

• Cornea—clear, outer layer on the front surface of the eye.
• Sclera—the “whites of the eyes.” This is the outermost layer of the eye (excluding the cornea).
• Retina—a thin layer of specialized sensory cells that line the inside of the back of the eye. It is responsible for capturing reflected light to send the image information to the brain via the optic nerve.
• Iris— the coloredpart of the eye that controls how much light moves through its opening (i.e. the pupil).
• Choroid—middle layer of the back of the eye.
• Lens—a clear, round disc behind the iris that focuses light onto the retina.
• Ciliary body—ring-shaped muscles that control the size of the pupil. It is also responsible for making aqueous humor.
• Aqueous humor—clear fluid that fills the portion of the eye in front of the lens.
• Vitreous humor—gel-like substance that fills the space between the lens and back of the eye.
• Iridocorneal angle (ICA)—the angle formed between the cornea and iris that determines how quickly aqueous humor flows out of the eye. Smaller or diseased angles will increase IOPs.
• Pectinate ligaments—a network of fibers at the ICA. The spaces in between the fibers act like drains for aqueous humor.

What causes glaucoma in dogs?

In glaucoma, the IOP increases because there is a decrease in drainage of aqueous humor. The aqueous humor is important for overall eye health. It keeps the lens clean and carries nutrients from blood to various eye structures. Once nutrients have been used up, it makes sense the older aqueous humor must be replaced by newer fluid.

In a normal dog, there is a delicate balance between aqueous humor production and drainage, which helps keep the IOP at a normal level. However, if aqueous humor cannot drain out of the eye via the ICA, the IOP may increase. This happens because the ciliary body is still producing new aqueous humor.

Think of it like plumbing—a damaged or clogged drain will cause water to back up in the sink if the faucet is not turned off. So, if aqueous humor cannot flow out of the eye, more of it will accumulate inside of the eye because it has nowhere else to go. And more fluid crammed into the same-sized space in the eye means the intraocular pressure will increase.

Types of glaucoma

Glaucoma is divided into two categories—primary and secondary. Primary glaucoma is typically inherited and is more common in purebred dogs. On the other hand, secondary glaucoma means that the increased IOPs are due to some other factor besides genetics. Primary glaucoma almost always affects both eyes whereas secondary may only affect one eye.

Primary glaucoma

Dogs with primary glaucoma have typically inherited one or multiple gene mutations that lead to malformations of the ICA (like closed angle glaucoma where a smaller ICA affects drainage flow) or of the pectinate ligaments (like in goniodysgenesis where the fibers are replaced by sheets of tissue). Think about this like trying to drain water through a colander with tiny holes instead of big holes.

In patients with open angle glaucoma, the ICA is normal-sized but cartilage building blocks called glycosaminoglycans (GAGs) accumulate in the network of pectinate ligaments, causing a physical obstruction. This is sort of like how the drain in your shower may become slower and slower as hair accumulates in it.

There are specific breeds that are more likely to develop certain gene mutations causing primary glaucoma. Genetic testing for these mutations is available for some breeds.

Dog breeds that are more prone to developing closed angle (i.e. narrow angle) glaucoma include the following:

• Akitas
• Basset Hounds
• Chinese Shar Peis
• Chow Chows
• Cocker Spaniels
• English Springer Spaniels
• Flat-Coated Retrievers
• Poodles
• Samoyeds
• Shiba Inus
• Shih Tzus
• Siberian Huskies

Open angle glaucoma is more common in:

• Beagles
• Norwegian Elkhounds
• Petit Basset Griffon Vendéens

For both primary and secondary glaucoma, gender does not appear to influence the risk of developing glaucoma. The age of onset is variable, but for primary glaucoma, middle-aged dogs are the most affected.

Secondary glaucoma

In secondary glaucoma, there are multiple eye issues that can lead to increased IOPs. Ocular trauma and lens luxations are among the most common causes. Uveitis (i.e. inflammation of the uvea, which is composed of the iris, ciliary body, and choroid) is also a contributing factor. For example, cataracts in dogs can cause uveitis which may then lead to glaucoma. Additionally, ocular cancer can affect aqueous humor drainage from the eye.

Health issues that can cause hypertension in dogs (i.e. elevated blood pressure) may also increase IOP. Some of these include heart disease in dogs and Cushing’s disease in dogs. In most cases of sudden onset glaucoma in dogs (i.e. acute glaucoma in dogs), there is an underlying problem of some sort that leads to secondary glaucoma.

Secondary glaucoma can affect most dog breeds because the contributing factors are numerous. However, Boston Terriers and Fox Terriers may be more at risk of developing lens luxations that can progress to glaucoma.

What are the symptoms of glaucoma?

Now that we’ve discussed the mechanics behind glaucoma and whom it affects, you’re probably wondering, “Is glaucoma in dogs painful?” The answer is “Yes.” In fact, glaucoma can be an extremely painful condition.

In addition to seeing signs your dog is in pain such a rubbing or pawing at the eyes or attitude changes, you may also notice the following signs of glaucoma:

• Corneal edema—a bluish-white discoloration of the cornea caused by fluid accumulation
• Episcleral injection—blood vessels that have become enlarged and more noticeable across the sclera
• Conjunctival hyperemia—redness of the normally pink tissues around the eye
• Mydriasis—dilated pupil
• Eye discharge
• Blepharospasm—excessive eyelid blinking and squinting
• Blindness

If you notice any of these signs, please make an appointment with your veterinarian promptly. Especially with sudden onset glaucoma, time is of the essence. High IOPs can damage the retina, sometimes permanently. So the sooner the vet is able to diagnose glaucoma and reduce the IOP, the better the chance of preserving the dog’s vision.

If the IOP remains elevated, a dog may progress to chronic glaucoma. Eventually, during end stage glaucoma, the eye may appear to be larger than normal (i.e. buphthalmos) and the dog may be completely blind in that eye. If the dog only has glaucoma in one eye, signs of vision loss may not always be very obvious because the “good” eye can compensate.

How will the vet diagnose my dog with glaucoma?

When you bring your dog to your veterinarian, he or she will perform a complete physical exam to look for signs of underlying health issues. Plus, your vet will thoroughly examine your dog’s eyes. Many veterinary clinics have a special tool called a tonometer. The vet can use the tonometer to measure a dog’s IOPs by briefly contacting the surface of the eye. Depending on the type of tonometer, your vet may place a drop of numbing solution in each eye to prevent discomfort during the examination.

Intraocular pressures are measured in millimeters of mercury or mmHg (just like atmospheric pressure). A normal range of values should be between 10 to 20 mmHg but can read as high as 24 mmHg with certain tonometer types. The vet will generally classify readings higher than 25 mmHg as abnormal. He or she may also suspect an eye issue if there is a difference of more than 8 mmHg between the two eyes.

It is important to note that one elevated value may not be enough to definitively diagnose glaucoma. The vet should repeat the tonometry and only suspect glaucoma when the IOPs are consistently high. It is also important for the veterinary team not to apply excess pressure behind the head or around the eyes when reading IOPs. This can falsely elevate the IOP. Additionally, the vet must keep in mind that IOPs can vary based on time of day or in a sedated dog.

Additional testing

Genetic tests for the mutations that lead to primary glaucoma are available for Shar Peis, Beagles, and Petit Basset Griffon Vendéens. Your vet may also recommend testing that looks for signs of other illnesses. For example, as mentioned previously, conditions that cause high blood pressure like heart disease, kidney disease, and various endocrine disorders (i.e. Cushing’s disease or hypothyroidism in dogs) can lead to secondary glaucoma.

In some cases, your vet may refer you to a veterinary ophthalmologist for further evaluation. These eye specialists have other tools for evaluating glaucomatous eyes. For example, they can use a unique lens to perform gonioscopy, which is the evaluation of the iridocorneal angle.

The overall appearance of the ICA can distinguish between secondary and primary glaucoma. They are also capable of performing some surgical procedures for glaucoma treatment and/or developing a medical management plan for cases of glaucoma that are difficult to control.

What is the treatment for glaucoma in dogs?

Once your vet diagnoses your dog with glaucoma, he or she will discuss the different treatment options. Overall, most canines with glaucoma respond better to surgical intervention in the long run. This is especially true for dogs with primary glaucoma or with lens luxations and ocular tumors. However, glaucoma surgery can be expensive, and isn’t the right option for all dogs, so medical management may also be reasonable.

Medical options

Sometimes the veterinarian may recommend starting with glaucoma eye drops or oral medications. These include:

Prostaglandin analogues

As mentioned earlier, acute glaucoma may damage the retina, leading to blindness. So in an emergency situation, severely elevated IOPs may warrant the use of a medication that rapidly lowers pressures in order to ideally preserve a dog’s sight. A class of topical eye medications called prostaglandin analogues can help with this. These medications, such as latanoprost, decrease resistance to aqueous humor outflow.

It is worth noting that prostaglandin analogues are only intended for short-term use. Additionally, they may cause temporary blindness because they constrict the pupils.

Carbonic anhydrase inhibitors

The most common type of glaucoma medication for long-term use is dorzolamide, which is a carbonic anhydrase inhibitor (CAI) drug. Inhibition of the enzyme carbonic anhydrase will decrease aqueous humor production. As a result, the IOP becomes lower.

Beta blockers

Your vet may also prescribe beta blocker medications like timolol because they also decrease the production of aqueous humor by the ciliary body. However, your vet must be cautious when using this drug in dogs with airway problems or heart disease.

Additional medications

If your dog develops secondary glaucoma due to uveitis, your vet may recommend topical steroid therapy. Additionally, all dogs with acute onset glaucoma and some with chronic glaucoma can benefit from oral pain medications.

In the event that medical management fails or is not an option,surgical treatment will be necessary. The surgical technique that the vet or veterinary ophthalmologist selects will depend in part on whether or not your dog still has vision in the affected eye.

Surgical options for visual eyes

If the dog can still see, the goal of surgery is to manage IOP and preserve vision for as long as possible. One option is a procedure called cyclophotocoagulation. In it, the veterinary ophthalmologistuses a surgical laser to destroy a part of the ciliary body. Doing so causes a decrease in aqueous humor production.

Sometimes, the veterinary ophthalmologist can implant a shunt that diverts aqueous humor around a diseased ICA so that it can leave the eye. This surgery is called gonioimplantation. The ophthalmologist may choose to combine it with cyclophotocoagulation in more difficult cases.

Finally, if the dog has a concurrent lens luxation, the veterinary ophthalmologist can surgically remove the lens. This should improve the secondary glaucoma.

Surgery for blind dogs

Unfortunately, sometimes glaucoma causes permanent blindness. In that case, the focus switches to keeping the dog as comfortable and pain-free as possible.

Enucleation

It may sound scary, but sometimes enucleation surgery is the best option for dogs with painful, blind eyes who are in end stage glaucoma. For this procedure, the vet or veterinary ophthalmologist will surgically remove the entire glaucomatous eyeball. From a cosmetic standpoint, your canine companion will look like he or she is permanently winking at you.

Although it may be difficult to think about your dog losing an eye, the great thing about enucleation is that it provides immediate relief from pain and discomfort. Dog parents often report that their dog starts acting like a puppy again after surgery because he or she is not in constant pain from the eye anymore. Additionally, enucleation is typically less expensive than the other surgical procedures and does not require specialized equipment. This often means your family veterinarian can perform the enucleation surgery.

I have run into many clients over the years who balk at the idea of enucleation. I get it. Your dog’s eyes are a beautiful, expressive part of who he or she is. But when his or her eyes are also extremely painful and no longer visual, something has to give. You might have to be willing to trade your dog’s eyes for more good days. In my opinion at least, that is a trade well worth making.

Intraocular prosthesis

If you would like to avoid enucleation surgery, your veterinary ophthalmologist can discuss a few other options. One involves the veterinary ophthalmologist removing the eye’s internal structures and replacing them with an ocular prosthesis for dogs. Some dog parents find this type of surgery more cosmetic than an enucleation. Plus, it does still provide pain relief. However, it is not a good option if the dog has ocular cancer, dry eye in dogs, chronic inflammation, or chronic corneal disease.

Gentamicin injection

Another procedure involves injecting gentamicin, an antibiotic, into the eye in order to destroy the ciliary body. This is only useful for cases of chronic glaucoma and has a 65-80% success rate. Ultimately, you may still need to consider enucleation if this procedure fails.

Are there home remedies for glaucoma in dogs?

There aren’t really any home remedies for glaucoma in dogs, but that doesn’t mean that what you do at home doesn’t matter. For example, it is important to administer the glaucoma eyedrops or oral medication according to your veterinarian’s instructions. And it is also critical to follow any post-op instructions should your dog have glaucoma surgery. Good nursing care and appropriate medication use can go far in helping your dog be as comfortable as possible.

If your dog is blind, there are also some things you can do to help him or her adjust. Although I didn’t design Dr. Buzby’s ToeGrips® dog nail grips with blind dogs in mind, I have had numerous people testify to how much they helped their blind dogs navigate the world with confidence. Being unsure of your footing can be unnerving for any dog, but especially for a blind dog. So it makes sense that the added traction of ToeGrips for blind dogs can be very reassuring.

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You can also help your blind dog by:

• Keeping furniture in the same location
• Always having the food and water in the same place
• Placing a rug or different textured surface at the doorways or stairs to help the dog know what is coming up
• Frequently talking to your dog so he or she knows where you are and feels reassured in new situations

For more ideas, check out my blog 7 Tips For Living With A Blind Dog.

What is the outlook for dogs with glaucoma?

Unfortunately, almost all dogs with primary glaucoma will eventually become non-visual. For dogs with secondary glaucoma, the prognosis depends on the cause since some causes are more treatable than others. Either way, it is important to remember that end stage glaucoma in dogs can be extremely painful. Please seek veterinary care as soon as you see the early signs of glaucoma. Prompt medical and/or surgical treatment can help your dog to be comfortable and visual for as long as possible.

When to put down a dog with glaucoma

The good news is that just because your dog has glaucoma, that doesn’t mean you should put him or her down right away. As you can see from the long list of treatment options I shared above, your vet has a lot of tools in the toolbox to help manage glaucoma. And even if your dog becomes blind, that doesn’t mean that his or her life is over.

Blind dogs can still have a wonderful quality of life with a dedicated owner and good pain control.

When you do get to the point where your dog isn’t coping well with being blind or you can no longer get the pain under control, then it may be time to have a conversation with your vet about whether preparing for your dog’s euthanasia is the kindest option.

But until then, keep your eyes on the future. Take steps to control your dog’s IOP with medications or surgery, be willing to do what it takes to minimize his or her pain (even if that means an enucleation), and stay in close communication with your vet. Hopefully, you and your dog will be able to enjoy many more wonderful years together after a glaucoma diagnosis and make many, many more lasting memories.

Has your dear dog been diagnosed with glaucoma?

Please share his or her story in the comments.