Glaucoma is one of the disorders that can affect dogs and cats without any visible signs. As with bloat, the fact that your pet is suffering is often not apparent until the situation is critical. At least glaucoma, unlike bloat, will not kill your dog or cat. Unfortunately, as with epilepsy, even if glaucoma is diagnosed in your cat or dog, there may not be much that can be done. Glaucoma in animals is not as readily treatable as it is in humans.
To understand what glaucoma is, it is first necessary to have some understanding of the structure and operation of the eye.
Animal and human eyes are basically balls filled with clear fluid, called aqueous humour. The pressure created from the presence of this fluid results in our eyeballs being round. If, like a water balloon, the fluid simply stayed there maintaining a constant level of pressure, we wouldn’t have glaucoma.
But unlike the water in a water balloon, the aqueous humour circulates within the eye, nourishing tissues. It is constantly draining through a sieve-like mesh of tissues behind the iris, and being just as constantly replenished as new fluid forms in the same area.
Nature has constructed the normal eye to maintain a constant level of acceptable pressure as the fluid drains and is refilled. Glaucoma occurs when this balance is interrupted.
When something occurs to stop the aqueous humour from draining properly, fluid builds up in the eye, causing excess pressure on the optic nerve. Too much prolonged pressure on the optic nerve causes blindness.
As one would expect, the pressure also causes pain; acute pain, akin to a migraine headache. In dogs and cats, the pain is much more severe than humans experience, as the pressure can reach much higher levels in our pets than in us. Normal ocular pressures are the same for humans as for cats and dogs: 10-20 mmHgs. A human with glaucoma would experience a pressure of 21-28 mmHgs, about double the normal pressure. But in cats and dogs, the pressure is often three to five times normal.
Veterinary medicine divides glaucoma into two types.
Primary glaucoma is an inherited condition. The animal’s genetics cause abnormalities in the angle of the eye’s drainage system. Eventually the drainage stops working properly and glaucoma results. Certain breeds of dogs are known to be at risk for primary glaucoma. Among these genetically predisposed breeds are Cocker Spaniels, Jack Russell Terriers, Bassets, Poodles, Chow Chows and Siberians.
Cats almost never have primary glaucoma.
Secondary glaucoma is where the circulation system is properly constructed, but it becomes blocked for some external reason.
There are many causes for such blockages. A common cause of glaucoma in cats is chronic inflammation of the eye. Sometime the lens of the eye becomes dislodged from its moorings, either through disease or trauma, and floats around in the aqueous humour. It may come to rest over the opening to the drainage area, causing a blockage. A blunt force injury to the head may cause bleeding behind the eye which results in a clot blocking the drainage system. Advanced cataracts or a tumour may also cause a blockage.
The main difference for your dog if their glaucoma is primary as opposed to secondary, is that with primary glaucoma, if it occurs in one eye, it will almost certainly happen in the other as well. If your dog loses one eye to glaucoma, the other will probably be in a similar condition within eight months; two years at most, even with treatment.
In the case of secondary glaucoma, because the cause is specific to that eye, the other eye will likely be spared.
Glaucoma can be acute (which means it comes on suddenly) or chronic (which means a slow buildup in the pressure and the hurt).
How do you know if your pet is experiencing this painful condition?
Unless it is acute, you probably won’t. With chronic glaucoma, the affected eye may become blind before the condition is apparent to the owner. Even then, because dogs and cats are good at compensating for physical disability as well as hiding pain, you may not even know that your pet is blind in one eye. Your pet will compensate and may appear perfectly normal. Loss of vision is not always easy to spot. If your pet is otherwise behaving normally and runs into a door or something, you might just think ”Klutz” and laugh it off. This happened with John’s Taffy.
Most animals with early to moderate chronic glaucoma are not taken to the vet, because there are no symptoms that anyone is likely to identify. Vets don’t routinely check eye pressures.
If your dog is a high risk breed, your vet may suggest checking the pressure in the eyes. If they don’t, ask.
Certainly any changes to the appearance of the eye should be immediately checked out by your vet. Glaucoma may cause the eye to bulge or become misshapen. Dilated pupils, cloudy eyes, red eyes, fluttering eyelids or even keeping an eye closed may be signs of a problem.
If only it was as obvious as this.
General, perhaps small changes in behaviour that we may not think are significant, like increased irritability, may betray pain.
With acute glaucoma, because the onset of pain is sudden and builds quickly, the dog or cat will be probably show unmistakable signs of distress; perhaps whining, pawing at their head or eyes, and be able to settle down. Loss of vision occurs within hours in some cases.
Treatments and prognosis depend on what is causing the glaucoma. The vet will look into the eye with special instruments to try to figure out what is causing the build up of pressure, in the hope that the underlying condition can be treated. But frankly, there is not a lot that can be done, even if the cause can be determined.
The first thing the vet will try are treatments to relieve the pressure in the eye. This will be done with medications which aim at both reducing the production of aqueous humour and trying to get the fluid to drain.
Treatments may be proposed to alter or kill the fluid producing cells, using cold temperatures or laser treatments.
But any of these treatments will only be effective at the very early stages. Even then, they may just slow the process down and not stop it.
If it is secondary glaucoma and the underlying cause can be both discerned and eliminated, the eye might be saved. This is a slim chance, and even if the eye is saved, it is almost certain that vision will be lost. The optic nerve, as with any other nerve, is unlikely to repair itself.
Medical treatment is not nearly as successful with pets as with people. For one thing, sensible humans who feel pain or other problems with their eyes, will get to an ophthamologist for diagnosis and treatment long before the condition is severe. As our pets don’t generally give unmistakable signs of distress unless it is acute glaucoma, the chances are high that the eye will already be in crisis with high pressures by the time treatment is sought. Medications often do not work at all for an eye with already high pressures.
Even where the treatment is given before the crisis arrives, medications often don’t work long term. They are costly and can be difficult to administer. When John’s dog Taffy experienced acute glaucoma, he had four different types of drops that were administered in different schedules over each 24 hour period, meaning that I had to get up twice in the night for ten nights to put them in (because John is deaf and can’t hear an alarm clock). How long can the most devoted owner keep up that schedule?
Cats with secondary glaucoma have a better prognosis with these medications, but the chance of failure is still high.
In any case, you have to think about your pet’s quality of life. Chronic pressure behind the eye is painful, even if the medications can control it to some extent.
A traumatic choice will almost certainly have to be confronted: is it better for your cat or dog to live like that, or to lose one or even both eyes?
Yes. The removal of the affected eye is the most likely solution to the problem of glaucoma in dogs and cats. A prospect to make the strong shrink back in horror.
Having been through it, I can tell you honestly that no matter how well braced you think you are, no matter how rationally and dispassionately you approach the problem, nothing can prepare you for the reality of seeing your dog emerge from the vet’s surgery with his eyelid sewn shut, taking hesitant steps instead of charging out to meet you.
Yet the reality is, your dog or cat will be much better off without the constant pain from that eye. The reality is, you will suffer more pangs of sorrow and pity than your pet will themselves. As I used to say to John when his Taffy lost his eyes, “For all he knows, the whole world has gone dark and we’re all stumbling around in the same way. It’s just a new factor in his life.”
If you and the vet decide the best thing for your dog or cat is to remove the eye entirely, you will have other decisions to make. The vet can simply sew the lids shut. They can put a sterile prosthetic ball in the socket before sew it up, in order to give the impression that the eye is still there.
Or you can have them implant an artificial eye and leave the lids open.
We chose the first option. Our vet told us that if we wanted the artificial eye, and to leave Taffy’s lids open, she would be happy to refer us elsewhere. But she herself would not do that procedure. Because there is no sight in that eye, there is no blink reflex. This means there is no way for the eye to clear out windblown particulates which enter the socket. This in turn leads to a high risk of infection.
We knew this was true from our own experience in the kennel. We boarded a Chow who had lost an eye and had an artificial one implanted. He had to have drops twice a day but they were ineffective in keeping the socket clean. That area was always a runny infected mess, no matter how often it was cleaned and disinfected.
Don’t be too alarmed by all of this.
Glaucoma has a very low rate of occurrence. Only 1.7% of dogs in North America get it. Poor Taffy was just one of the unlucky ones.
And although the experience is painful for your pet and traumatic for both of you, it is at least not life threatening. Most blind pets, in our experience, adapt quite well to their condition. It is important of course to make sure they have a safe and secure environment.
And if this should happen to your pet, remember that dogs and even cats rely much more on their sense of smell and hearing than on their eyesight. Their quality of life can be excellent.