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                           Glaucoma in dogs & cats

What is Glaucoma? 

Glaucoma 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. Aqueous humor circulates inside the eye. 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.

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. It is critical to treat the cause of the glaucoma whenever possible.

Diagnosis of Glaucoma

Diagnosing whether the dog has primary or secondary glaucoma is important because the treatment needed and the prognosis for vision is different for each type of glaucoma. Veterinarian measure the intraocular pressure (IOP) and, 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 tonometer is the TonoVet™; these are costly computerized handheld devices. 

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. 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?

You don’t. The only way to know if your pet has glaucoma is to have the IOPs measured by a veterinarian, preferably a veterinary ophthalmologist. It can be difficult to accurately measure the IOP is the patient is in pain and/or agitated. 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 Rx™ (see www.ocuGLO.com ).

How is Glaucoma treated?

Acute glaucoma may require emergency hospitalization. Veterinarians use various topical and oral drugs to lower intraocular pressure. Mannitol may be used in the short term to lower pressure.

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 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 Alternative Medicine (CAM).

Complementary alternative medicine therapy consists of lifetime supplementation with a pharmaceutical-grade canine antioxidant vision supplement, Ocu-GLO Rx™ (see www.ocuGLO.com). 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. 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, then there are choices for treatment. The most common choice is lifetime prophylactic medical treatment (glaucoma eye drops) and frequent IOP measurements. Complementary alternative medicine (CAM) for these patients is also strongly recommended, consisting of lifetime supplementation with a pharmaceutical-grade canine antioxidant vision supplement, Ocu-GLO Rx™ (see www.ocuGLO.com). 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 or deeply sedated.

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.

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.

Which procedure is best for your pet depends on the type of glaucoma, the potential for vision, your preference for the cosmetic appearance of your pet's face, and cost. Glaucoma is a very frustrating disease because it requires constant monitoring, may require several different therapies, has a high cost financially, and despite excellent care often still results in permanent vision loss. The key to having the best chance of preserving vision is early detection, excellent owner compliance in treating the, eye(s) daily as prescribed, and regular ophthalmic examinations. One way to help with early detection is to test your pet's vision daily–throw a toy, or a treat, etc. Challenge their vision and see how well they perform.

It is also important to know that if your dog or cat loses vision in both eyes from glaucoma, that it is extremely likely that they will adjust very well to their vision loss, as long as their eye(s) are comfortable. Remember–glaucoma causes a migraine headache-like pain, and your pet will NOT tell you that it has a headache. Take care of the discomfort in order to give your pet the best possible quality of life. Sadly, some animals with glaucoma have had to have both eyes removed. This is not the end of the world–they adjust very well to their vision loss, especially when they no long hurt! It is much harder for the owner to accept, but if the owner follows the example of how their pet learns to adapt, they will get through this difficult time of grieving the loss of their pet's vision.

Please remember: Glaucoma can cause blindness in spite of our best efforts. A high level of commitment to treatment and regular ophthalmic examinations is required to have the best chance of preserving vision. If your pet is diagnosed with primary glaucoma, please notify the dog's breeder. They need to know!


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