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What is Glaucoma?
What causes Glaucoma?
How does Glaucoma affect the eye?
How do I know if my pet has Glaucoma?
How is Glaucoma treated?

What is Glaucoma?

G laucoma is increased pressure within the eye (intraocular pressure = IOP ). Cells inside the eye produce a clear fluid (“aqueous humor”) that maintains the shape of the eye and nourishes the tissues inside the eye. (Note: aqueous humor is NOT the same fluid as tears. Tears bathe the outside surface of the eye. Aqueous humor circulates inside the eye. These two fluids do not interact). The aqueous humor drains out of the eye into the bloodstream through the drainage angle–a sieve or meshwork-like area through which aqueous percolates out of the eye. The balance of aqueous fluid production (“the faucet”) and drainage (“the drain in the sink”) is responsible for maintaining normal pressure inside the eye. In glaucoma, the drain becomes partially or completely clogged but the “faucet” steadily keeps producing aqueous, causing pressure to build inside the eye. If untreated, this increased pressure usually causes irreversible blindness, in addition to stretching and enlargement of the eye.

What causes Glaucoma?

Many different conditions can cause glaucoma. Glaucoma is classified as either primary or secondary in animals.

Primary Glaucoma is an inherited condition. Primary glaucoma occurs in many breeds of dogs, including the American Cocker Spaniel, Basset Hound, Chow Chow, Shar Pei, Jack Russell Terrier, Shih Tzu, and Arctic Circle breeds (including the Siberian Husky and Elkhound). Primary glaucoma is rare in cats.

Primary Glaucoma usually begins in one eye, but in most patients it eventually affects both eyes, leading to complete blindness if not controlled.

Chronic glaucoma in right eye of a dog, causing eye enlargement and secondary lens subluxation.

Secondary Glaucoma occurs when other eye diseases cause decreased drainage of fluid from the inside of the eye. Common causes of secondary glaucoma include: inflammation inside the eye (uveitis); advanced cataracts; cancer in the eye; lens subluxation or luxation (i.e. displacement of the lens from its normal position; a completely luxated lens is free of all attachments and can “float around” inside the eye, causing both damage and pain) and chronic retinal detachment. Glaucoma in cats is almost always secondary to chronic uveitis. Treatment for secondary glaucoma is too broad to be presented here; it is critical to treat the cause of the glaucoma whenever possible.

Patients are often more relaxed at our quiet and peaceful office, making it easier to obtain accurate IOPs.

Patients are often more relaxed at our quiet and peaceful office, making it easier to obtain accurate IOPs.

Diagnosing whether your dog has primary or secondary glaucoma is important because the treatment needed and the prognosis for vision is different for each type of glaucoma. Veterinary ophthalmologists measure the intraocular pressure (IOP) and use slit lamp biomicroscopy, indirect ophthalmoscopy, and gonioscopy to determine the type and cause of glaucoma in your pet. Tonometry is measurement of IOP, and there are three basic types of instruments (tonometers) that can be used to measure IOP. The best tonometers are the TonoPen™ and the TonoVet™; these are costly computerized handheld devices. Another device is a Schiotz tonometer; this is an inexpensive stainless steel device, but is more difficult to use in animals. Gonioscopy helps determine how predisposed the remaining visual eye is to develop glaucoma when primary glaucoma is present in the other eye–i.e. what is the risk level of the remaining eye to develop glaucoma? Gonioscopy involves placing a special contact lens (“goniolens”) on the eye, which allows examination of the drainage angle. Gonioscopy is usually performed under sedation.

How does Glaucoma affect the eye?

  • Pain. Increased intraocular pressure (IOP) is painful. Dogs, cats, and humans have normal IOPs between 10 and 20 mmHg. Glaucoma often results in pressures of 20–28 mmHg in humans, but pressures of 30 mmHg and higher (often higher than 50 mmHg!) are common in dogs and cats. For this reason, glaucoma in pets is usually much more painful than glaucoma in humans. The pain persists in the form of a constant headache or migraine. Animals show pain in different ways than humans do–in ways that are often not noted by the owner. Pain from glaucoma is usually not obvious to most owners–it can result in decreased activity, less desire to play, irritability, and/or decreased appetite–but is often not apparent at all to the owner. There is usually no squinting nor rubbing of the eye… Your pet will not let you know that they have a headache and that their eye is uncomfortable.

  • Vision Loss. The first tissue to die when glaucoma occurs is the optic nerve. Optic nerve tissue is like brain tissue; once cells in the optic nerve are damaged, it is difficult for them to heal. Pressure damage to the optic nerve and decreased blood flow to the retina (the “film in the camera”) results in loss of vision. However, if the pressure in the eye remains uncontrolled, the optic nerve and retina degenerate and vision is permanently lost. Permanent blindness can occur within hours if the pressure is very high and the glaucoma develops rapidly.

Unfortunately, the first eye to develop primary glaucoma in dogs is usually already irreversibly blind by the time glaucoma is diagnosed. For this reason, treatment for these patients is directed towards relieving discomfort (i.e. migraine headache) in the blind eye and trying to prevent or delay glaucoma from occurring in the other eye. Gonioscopy of the remaining visual eye helps determine how to best try to save this eye.

How do I know if my pet has Glaucoma?

Acute Glaucoma in a Chow Chow. The eye is blind.

You don’t. The only way to know if your pet has glaucoma is to have the intraocular pressures (IOPs) measured (this is called “tonometry”) by a veterinarian, preferably a veterinary ophthalmologist. It can be difficult to accurately measure the IOP if the patient is in pain and/or agitated. Additionally, we have to contend with the “white coat effect”— this refers to the stress that a patient (dog, cat, or human) experiences when they visit their doctor’s office. This stress can cause temporarily increased blood pressure and/or increased eye pressure. Animals visiting their family veterinary clinic might be too anxious for staff to obtain an accurate IOP measurement. It is often necessary for patients with glaucoma to have their IOPs monitored at Animal Eye Care instead of at their family veterinary hospital because of stress-related issues; our office is quiet and peaceful. Sometimes this stress can be controlled at the family veterinary clinic by allowing the pet and owner to sit quietly in an exam room and dim the lights for 10-15 minutes before tonometry is performed. The key is a quiet, relaxed patient. Making the patient wait in a crowded, noisy reception area will interfere with obtaining an accurate IOP reading. If a general practitioner veterinarian diagnoses (or suspects) that glaucoma is present, the next step is to refer the patient to a veterinary ophthalmologist ASAP. The sooner that glaucoma is properly diagnosed and treated, the better.

Signs of glaucoma can include a red or bloodshot eye and/or cloudy cornea (the “clear windshield” part of the eye). Often the eye looks normal to the pet owner–or even to the general practitioner veterinarian–but it is not. Vision loss is also characteristic of glaucoma. However, loss of vision in one eye is usually not obvious because animals compensate very well by using their remaining visual eye. Eventually, the increased IOP will cause the eye to stretch and enlarge. Unfortunately, by the time the owner notices the enlarged eye, it is too late–eyes are permanently blind by the time they are obviously enlarged.

What if one eye is already lost to Primary Glaucoma? It is very likely that the remaining visual eye is at high risk for also developing glaucoma at a future time. Research has shown that the median time until a glaucoma attack occurs in the remaining visual eye is 8 months . However, prophylactic medical therapy and regular monitoring of the IOP for the remaining eye can delay the onset of glaucoma from a median of 8 months to a median of 31 months . The onset of a glaucoma attack might further be delayed by also providing the dog with a daily canine antioxidant vision supplement, Ocu-GLO™ (see ).

How is Glaucoma treated?

Since glaucoma occurs because fluid is not draining from the eye fast enough, the logical treatment is to open up the drain. Unfortunately, opening the drain and keeping it open is difficult in animals. Therefore, many glaucoma therapies are also aimed at decreasing fluid production by the eye.


  • Medical Therapy. There are several different types of costly glaucoma eye drops and pills that help decrease fluid production or increase fluid drainage from the eye (or both). While these medications are helpful in animals, they usually do not control glaucoma long-term, and often don’t work at all for an eye in crisis. Consequently, they are used mostly to help prevent or delay the onset of glaucoma in the remaining visual eye, and as temporary treatment until surgery can be performed in the affected eye if the eye still has some vision or real hope of vision. CAM (Complementary and Alternative Medicine) is also recommended (see below). However, in cats with secondary glaucoma, the eye has a better chance of medical control of glaucoma than in dogs with primary glaucoma. Still, lifetime medical treatment is costly for cats too, and may ultimately fail.

    If the affected eye is NOT blind, lifetime medical therapy and CAM (see below) can be elected, but it has a high failure rate. The best chance for saving vision in these eyes is a combination of surgery (endolaser cyclophotocoagulation = ECPC) and medical and CAM therapies.
  • Complementary and Alternative Medicine (CAM). Complementary and alternative medicine therapy consists of lifetime supplementation with a pharmaceutical-grade canine antioxidant vision supplement, Ocu-GLO™ (see ). Specific antioxidant nutraceutical support of the eye can help reduce oxidative damage in the cells inside the eye that are responsible for proper drainage of fluid. Ocu-GLO™ has also been shown to be neuroprotective in a research model of mice with genetic glaucoma: in other words, Ocu-GLO helps to protect optic nerve cells from dying when glaucoma is present. It is also important to help control stress –if the dog has chronic stressors in its life, this can negatively affect the general health, immune system, and the ability to ward off oxidative damage in the body–including the eyes. It is also important to reduce pressure on the jugular veins in the neck, as this can increase the IOP if the dog is pulling on a leash attached to a neck collar. Dogs with glaucoma or at risk of developing glaucoma should have leashes attached to harnesses and not neck collars, to prevent pressure on the jugular veins (which can in turn increase IOP and trigger a glaucoma attack).

    If the dog has already lost one eye to primary glaucoma and the remaining eye is at high risk for developing glaucoma, there are choices for treatment. The most common choice is lifetime prophylactic medical treatment (glaucoma eye drops) and frequent IOP measurements. Complementary and alternative medicine (CAM) for these patients is also strongly recommended, consisting of lifetime supplementation with a pharmaceutical-grade canine antioxidant vision supplement, Ocu-GLO™ (see ). Controlling stress and using leashes attached to harnesses are also important.

    Note: If the eye is blind, controlling glaucoma with long-term medical and CAM treatment is usually not the best choice, because eventually it fails, requiring surgery to relieve chronic discomfort. Medical treatment delays the inevitable, in most cases. Why commit to lifetime medical treatment for an eye that will never see again? Also, the cost of glaucoma medications and ophthalmic examinations is not cheap–usually this is a far greater expense than the cost of removing the blind eye. Do not be fooled into thinking that your pet’s blind, enlarged, glaucomatous eye is not bothering them. It is. Besides surgical eye removal, there are other surgical choices depending on the desired cosmetic outcome, cost, and the patient’s general health. For example if the pet is not in good general health, then a prolonged surgery under general anesthesia might not be possible. However, there is a very brief procedure (for dogs only) called intravitreal injection (or “chemical ablation”, or “pharmacologic ablation”) in which a drug that lowers the IOP is injected into the eye while the dog is briefly anesthetized. (see chart below).
  • Surgical Therapy. The type of surgical procedure chosen to treat glaucoma in animals depends upon whether or not the eye still has the potential for functional vision. For visual (or potentially visual) eyes with glaucoma , the IOP can be controlled by performing delicate endolaser cyclophotocoagulation (ECPC) laser surgery, in which a laser probe is inserted into the eye and the laser beam selectively destroys some of the cells that produce the fluid. In order to position the laser correctly inside the eye, the lens must first be removed; after the surgery is done, an artificial lens is placed in the eye. Sometimes a third procedure is also performed right after the artificial lens is placed – inserting an artificial drainage device into the eye. ECPC is a very complicated procedure, and is performed by very few veterinary ophthalmologists. If this surgery is recommended for your dog by Dr. McCalla, she can discuss with you where the surgery can be performed. For permanently blind eyes, the choices are: the eye can be removed (enucleated) with the option of placing a sterile prosthetic ball implant in the eye socket prior to skin closure; an implant can be placed inside the eye giving the pet a partially artificial eye; or an injection of a drug into the eye can be performed, that kills the fluid-producing cells and reduces the pressure.



(Dogs only): Endolaser Cyclophotocoagulation/lens removal/artificial lens placement/ +/- drainage device placement, FOLLOWED BY Lifetime Medical Therapy and CAM (Complementary and Alternative Medicine).


Cells in the eye that produce fluid are killed by a laser beam, after first removing the lens. Then an artificial lens is inserted, followed sometimes by inserting an artificial glaucoma drainage device.

Lifetime medical therapy and supplementation with canine antioxidant vision supplement (Ocu-GLO™); Control of stress; Use a harness attached to the leash instead of neck collar.

Lifetime regular IOP measurements/ophthalmic examinations

Lifetime Medical Therapy and CAM

Dogs and Cats: Topical (and sometimes oral) medication to control intraocular fluid production and increase fluid drainage. Lifetime regular IOP measurements/ophthalmic examinations
Dogs: Lifetime supplementation with canine antioxidant vision supplement (Ocu-GLO™); Control of stress; Use a harness attached to the leash instead of a neck collar.
Dogs and Cats: Lifetime regular IOP measurements/ophthalmic examinations.

Note for Cats: Treat cause of glaucoma; Control stress; Consider antioxidant supplementation.





Removal of the eye, and then the eyelids are sutured closed. This surgury is usually performed by your family veterinarian.

Enucleation and Orbital Prosthesis.Not recommended for cats.

Removal of the eye. A black prosthetic ball is then placed in the orbit and the eyelids sutured closed. It prevents “sunken-in” appearance of skin over eye socket. Performed at Animal Eye Care.

Evisceration and Intraocular Prosthesis

2 months post-operative appearance of eye with intraocular prosthesis.

The inside contents of the eye are removed and replaced with a prosthetic ball. This leaves your pet with a gray, non-painful eye that has no vision, but blinks and moves. Performed at Animal Eye Care.