Similar to glaucoma in humans or glaucoma in dogs, feline glaucoma occurs when the fluid inside the eye, located directly behind the lens, builds up and does not drain properly.
This fluid is called aqueous humor, and is not to be confused with tears which coat the outside of the eye. Tears and aqueous humor do not interact or perform the same functions. Aqueous humor is inside the eye only, and is there to help support and maintain the shape of the eye as well as nourish delicate structures and tissues.
This fluid is produced by something called the ciliary body and drains back into the blood stream as a way to keep pressures inside the eye within normal limits. This pressure inside the eye is called intra-ocular pressure, or IOP. When production of fluid and drainage of fluid stays about the same, IOP will remain pretty steady.
However, if there is too much IOP, as with glaucoma, the imbalanced pressure pushes against fragile internal structures of the eye and presses against the optic nerve. If there is long-term pressure against the delicate inner workings of the eye, it can cause severe and lasting damage, and even permanent blindness.
Normal IOP in humans and cats (dogs too) ranges from 10-20 mmHg. When humans experience glaucoma, their pressures can be measured as anywhere from 20-28 mmHg. Animals seem to have the sharper end of the stick, as IOP in animals with glaucoma can reach 30-50 mmHg and higher, causing enormous pressure and pain alongside any damage.
Types of Cat Glaucoma
Just as with dogs, cats experience primary and secondary glaucoma. Primary glaucoma is a result of physical and physiological eye abnormalities like an improper drainage angle, causing an increase in IOP.
The abnormality is usually genetic, and breed-related. Unlike dogs, primary glaucoma is a rare occurrence in cats. When it does happen however, it’s almost inevitable that the cat will get glaucoma in both eyes.
More common in cats is secondary glaucoma, which can occur in one or both eyes. Vets are unable to predict whether or not a cat will be infected in both eyes or not, as it can be somewhat random. A feline may experience severe glaucoma in one eye, even to the point of permanent blindness, and never get it in the other one.
Secondary glaucoma can be related to eye inflammation, called uveitis, where the inside of the eye becomes inflamed. Intra-ocular infections that cause scar tissue and debris to hinder the drainage of fluid can trigger glaucoma.
Tumors of the eye, cataracts, as well as luxation and subluxations, where the lens slips out of place inside the eye can also cause damage that hinders drainage. A ruptured lens, often from injury or trauma can create swelling, which interferes with the drain angle. Blood clots in the eye are also culprits of glaucoma, causing increased IOP and blocking healthy drainage of aqueous humor fluid.
When pressure is high, the inner lining of the eyeball called the retina, as well as the optic nerve carrying signals from the retina to the brain telling your cat how to see, are compressed, resulting in impaired vision.
Symptoms of Glaucoma in Cats
As with dogs, signs of glaucoma in cats can be very subtle, so much so that it can go entirely unnoticed, and more often than not, undiagnosed. The disease often presents late in the game, with an onset that is gradual and insidious, causing irreversible damage.
As pressure increases, one eye can appear to be slightly larger than the other, and one or both eyes could have a cloudy appearance to them that gets progressively worse. You may notice an unresponsive dilated pupil, or your cat walking around with a slight squint.
Behavior changes can happen, although they may not be obvious either, if they occur at all. The advancement of glaucoma can be so subtle that any signs at all can be missed for months or more, especially if your cat continues to behave and play normally. Frequent and/or rapid blinking could be a sign, and sometimes the affected eye may roll back into the head.
Obvious loss of vision can also occur, although you may not always realize your cat has gone blind because like any animal, they learn quickly how to compensate for the loss. Pain and headaches are also a symptom, and your cat may communicate their pain to you by pushing their head against something in an attempt to relieve the ache. Or your cat could show no clinical signs of pain at all.
In secondary glaucoma, the same symptoms apply. In addition, blood vessels in the whites of the eye may appear more red than normal, or visible debris in the eye could cause an inflammatory response. You may be able to see the iris ‘sticking’ to the lens or cornea, which obstructs drainage and incurs damage. Your cat may also suffer from a loss of appetite.
Glaucoma in cats is not ‘curable’ although pain and symptoms can be managed.
Risk Factors of Glaucoma in Cats
Primary glaucoma is genetic and rare. Breeds that have a predisposition for glaucoma are Siamese, Persian, and Burmese cats, as well as domestic long and short-haired breeds. Middle-aged felines and older are the most susceptible.
Secondary glaucoma is more common, making up 95-98% of all cases of glaucoma in cats, and it most often presents in adult cats. IOP is the biggest risk factor, but it can be difficult to make a diagnosis. Cats can also suffer from ocular hypertension which can cause elevated IOP levels without any evidence of glaucoma. A cat’s mmHg can fluctuate quite a bit, causing difficulty in determining an accurate diagnosis. IOP can also be lowered in advanced glaucoma, as degeneration of the ciliary body can reduce aqueous humor production.
Cataracts, tumors, blood hemorrhage, eye infection and inflammation, and luxation are all risk factors of secondary glaucoma and can be the flame that ignites the degenerative disease.
Can Feline Glaucoma Be Prevented?
Glaucoma can’t really be prevented, but you can manage it and slow down the progression if it’s caught early enough. Regular vet visits and are important, as well as being proactive in self-assessments of your pet to look for signs of anything that may be amiss. Any infections, especially eye infections, should be treated right away and as directed by your vet. Try to make sure your feline is not exposed to unsafe environments, as an eye injury can turn into glaucoma very easily.
If glaucoma is suspected, do not delay with making an appointment with an eye specialist, as the longer your wait, the more the potential damage to the eye or eyes. To have any hope at preventing total vision loss, it’s important for a cat with suspected glaucoma to be cared for right away.
Diagnosis and Treatment of Glaucoma in Cats
If it’s caught early enough, glaucoma progression can be slowed down considerably using a variety of treatment methods. Sadly, your pet may already be blind in one eye before a definitive diagnosis is made, but fortunately, animals are highly adaptable and wind up compensating for the loss extremely well.
Treatment in such cases will address pain relief of the afflicted eye, relieving the pressure, as well as attempts to save the other eye from a similar fate. Treatments will vary depending on the type of glaucoma and the root cause, so it’s important for you and your vet to figure out why your cat has developed glaucoma in the first place to determine the best course of care.
Your feline ophthalmologist may use a tonometry to measure eye pressure, and send your cat for x-rays. Ultrasounds are sometimes used as well, so any tumors or abnormalities can be seen. Your vet may decide blood tests are necessary, including chemistry tests and specialty tests, blood counts, urine tests, thyroid tests, special cultures, tests for feline leukemia and immunodeficiency virus, and more. All of these can help rule out various underlying causes so that you and your vet can provide the most targeted treatment.
For most cats who are blind in one eye, the best long-term care option may be to remove the eye entirely. If looks are important, you can always look into a prosthetic eye to replace the missing appendage. But removal is the kindest and ultimately the least expensive option for a feline suffering from continual pain. Long-term treatments with medications and vet exams can rack up a large medical bill that you may not be prepared for.
If removing the eye is not yet an option, there are medications your pet can be given, both oral and topical. Many meds are designed to decrease how much aqueous humor fluid the eye produces, as it’s more difficult to unblock the drain and keep it that way than it is to reduce the amount of fluid that needs to drain in the first place.
Remember though, that medications and supplements are simply delaying the inevitable, so you will need to decide for yourself if that’s really the best route for your pet, or if surgery might be a better solution.
Just as with dogs, stress reduction is also very important in your cat’s environment, because excessive stress causes oxidative damage inside the body that can affect even the eyes. Stress reduction is recommended both as a treatment for current glaucoma cases, and as a preventative.
When it comes to surgery, it largely depends on whether the eye still has vision potential or not. If there is still potential for your pet’s vision to be saved, IOP can be reduced by cycoablation and implants. For pets already blind, removal may be recommended, or sometimes drug injections might be possible. These injections are designed to kill the cells producing aqueous humor fluid, thus relieving the build-up of pressure.
At the end of the day, permanent blindness can be an emotional blow for you, but you will discover that your cat is amazingly resilient. Their other senses will be enhanced by their vision loss, so smell, hearing, and touch will help them exponentially. Whiskers and vibrissae hairs located on their face and feet help them ‘feel’ their environment, and as with any victim of blindness, things you do can be very helpful.
Keeping the layout of your home the same, making sure there aren’t any ‘roadblocks’ that will cause your feline to trip, and just keeping things as normal as possible for your pet are all great ways to help them cope and adjust. Keep necessities exactly where they’ve always been, and use sound to help train your cat and warn them when you are nearby.
Ultimately, even though your cat may not be able to see you, they love you just the same as they always did. It’s now your job to love them back equally as much.