Overview of Canine Glaucoma
Glaucoma is abnormally high pressure in the eye of the dog. Inside the normal eye there is constant production and drainage of a watery fluid called aqueous humor. When there is a problem with the drainage of the fluid, the pressure within the eye can increase. High pressure causes damage to the optic nerve, which, in turn, causes vision loss. Causes of glaucoma can be primary or secondary.
Primary glaucoma indicates a problem in the area where fluid leaves the eye. The problem can be structural or one that involves the function of the drainage area of the eye. This form of glaucoma has a tendency to be inherited and is very common in the dog. The age of onset can vary among dog breeds.
Secondary glaucoma develops as a side effect of some other disorder within the eye. Many different eye diseases can interrupt the usual flow of aqueous humor within the eye or disrupt the drainage of this fluid from the eye.
Causes of Glaucoma in Dogs
The exact precipitating cause of primary glaucoma is unknown. The disease appears to occur spontaneously, often without any warning. Even though the drainage area of the eye may be abnormal since birth, it is not understood why acute glaucoma appears at a particular time, later in life.
Secondary glaucoma is also an important form of glaucoma in the dog and has numerous causes, including the following:
Inflammation – Severe inflammation in the eye produces protein and debris that circulate with aqueous humor. This material can clog up the drainage area and block the outflow of fluid. Fluid flow may also be blocked at the pupil if an inflamed iris sticks to the lens, which sits immediately behind it. Chronic inflammation of the iris is a common cause of glaucoma in the dog.
Lens luxation – If the lens becomes dislocated (luxated) and falls into the front chamber of the eye, it can block the flow and drainage of aqueous humor. Primary lens luxation is an inherited condition in certain breeds of dogs, including the terrier breeds, Border collie, and Australian blue heeler. In these dogs, there is premature breakdown of the fibers that hold the lens in place and the lens can start to move around within the eye. Lens luxation can also occur secondary to other changes in the eye, such as cataract formation and tumor growth.
Tumors – Tumors inside the eye can invade the drainage area and prevent fluid from leaving the eye.
Trauma – If the eye somehow gets injured, it can fill with blood, which may block the drainage pathway.
What to Watch For
Very squinty and painful eye
Dilated pupil that doesn’t react to light
Cloudy (whitish/blue) cornea (front surface of the eye)
Enlarged size of the eye (known as buphthalmos)
Glaucoma generally only affects one eye initially. Depending on the underlying cause, the other eye may be at risk for developing glaucoma in the future.
Diagnosis of Glaucoma in Dogs
Diagnostic tests are needed to recognize glaucoma and exclude other diseases. Tests may include:
A complete medical history and general physical examination of your pet. The need for blood work and other general health tests varies.
A complete exam of the eye to confirm the presence of glaucoma and to determine if the glaucoma is primary or secondary. The eye is also assessed for the amount of damage that has been done to the optic nerve and retina. Your veterinarian may refer your dog to a veterinary ophthalmologist for a comprehensive examination of the eye, which would include:
Frequent measurements of the pressure inside of the eye (called tonometry)
Gonioscopy to evaluate the drainage pathway with specialized instrumentation
Ultrasonography of the eye if the eye is too cloudy to be examined in depth. It can help identify lenses that are out of place, tumors, and damage to the optic nerve.
Treatment for Dogs with Glaucoma
The primary goals of the treatment of glaucoma are to treat or correct any underlying causes, to decrease the pressure within the eye, and to save vision if possible. Treatment of glaucoma in dogs may be medical or surgical.
Medical therapy attempts to decrease the production of fluid within the eye, to improve the flow of fluid out of the eye and to control any inflammation within the eye. Both topical medications (drops placed directly on the eye) and systemic medications (pills or injections) are available for treating glaucoma.
Surgical therapy is used for treating primary glaucoma in the dog. Such surgical therapy involves killing the area within the eye that produces aqueous humor. This may be done with either cryotherapy (freezing) or laser therapy. Another option involves bypassing the drainage area by inserting tubing with a valve into the eye. All of these procedures are performed more often in dogs that still have some potential for vision. They are not popular remedies for dogs with blind eyes, although they can be tried in blind dogs.
Surgical therapy for lens luxation involves opening the eye and removing the dislocated lens manually.
When a tumor is present in the eye and causing glaucoma, surgery to remove the eye (enucleation) is indicated.
When glaucoma does not respond to medications or surgery and the pressure within the eye remains elevated, when the animal is persistently painful, or when the eye is blind and glaucoma therapy is too expensive to continue, then surgical removal of the eye may be considered.
Home Care for Dogs with Glaucoma
Glaucoma is a very difficult problem to treat. Medications must be administered at consistent times and must often be continued indefinitely. It is important to administer glaucoma medications exactly as your veterinarian prescribes them. Medications should not be stopped just because the appearance of the eye has improved. In the event that vision cannot be saved, understand that such vision loss is not life threatening and the vast majority of dogs adjust very well to impaired vision or blindness in one or both eyes.
Information In-depth for Glaucoma in Dogs
Glaucoma is an elevation of the pressure within the eye that is incompatible with normal function of the eye. It is a disorder of the outflow of fluid (aqueous humor) from the eye and not a disease of overproduction of fluid within the eye. Sudden, high elevations of pressure within the eye are common in the dog and can occur without warning over several hours. These acute elevations in pressure can cause devastating and irreparable damage to the retina (which acts like the film a the camera) and the optic nerve (which sends information from the eye to the brain).
The causes of glaucoma are both primary (spontaneous, probably inherited) and secondary (arise in association with other diseases within the eye).
Primary Glaucoma in Dogs
The list of predisposed breeds is long, but some of the most commonly affected dogs are the American and English cocker spaniel, basset hound, beagle, chow chow, Chinese shar-pei, Siberian husky, Dalmatians, Great Danes, Bouvier des Flandres, Boston terrier, Norwegian elkhound, Samoyed, English and Welsh springer spaniel, Alaskan malamute, poodle, and shih tzu.
The fluid outflow pathway in the eye is commonly known as the drainage angle. For proper outflow, the angle needs to be open and functioning properly. The drainage area looks and acts almost like the sieve in a kitchen drain. In many breeds of dog, this drainage angle can be abnormal. Either the access to the sieve is narrow, there are too few drainage holes, or the drain behind the sieve does not work properly. Even though the fluid passes through the sieve it does not drain into the veins around the eye well and backs up, causing the pressure in the eye to increase.
Secondary Glaucoma in Dogs
Inflammation within the eye that gives rise to glaucoma has many different causes. In the dog, chronic anterior uveitis (an inflammation of the iris and surrounding tissues) is a common cause of secondary glaucoma. Chronic uveitis may arise with certain infectious diseases such as Lyme disease or fungal infections, or as a side effect of cataract development (lens-induced uveitis). In some cases of chronic inflammation, the cause is never determined. One or both eyes may be affected by the inflammation, and one or both eyes may develop glaucoma.
Tumors within the eye generally occur in older pets. Only one eye is usually affected and the progression to glaucoma may be relatively slow.
Trauma can happen to any unrestrained dog, at any age. Trauma might include being hit by car, being hit in the head, falling, or being attacked by another animal.
Primary lens luxations (dislocations) are much more common in the terrier breeds. These breeds include the Parson Russell terrier, Tibetan terrier, Sealyham terrier, smooth and wirehaired fox terrier. The Border collie, Australian blue heeler, and individuals in some other dog breeds may also develop primary lens luxations. It is believed that these dogs have an inherited premature degeneration of the fibers that hold the lens in place. Once the fibers holding the lens break down, then it is free to move around within the eye. When the lens moves in front of the pupil, severe acute glaucoma can develop within hours.
Secondary lens luxations are more likely to cause slow-developing or chronic glaucoma. The lens may dislocate in association with cataract development, the growth of tumors within the eye, and progressive detachment of the retina.
What to Watch For with Canine Glaucoma
Many diseases can cause a red, squinty, teary and cloudy eye, but glaucoma should always be considered as a cause. Frequently when the pressure is high, the dog is quite painful and holds the eye closed or keeps the third eyelid (a pink/red membrane) up over the eye.
If the pressure inside the eye remains elevated for sometime, the eyeball may actually stretch and enlarge. As the eye enlarges or becomes buphthalmic, the eyelids may no longer be able to protect the surface of the eye, and the eye may be traumatized easier.
Assessing vision in the dog can be difficult. Your pet should blink and try to close the eye when a very bright light is shown into the eye. Without creating airflow, see if your dog blinks when you wave your hand in front of the eye (known as a “menace test” because your pet is responding to a menacing gesture). You can also try to throw objects like cotton balls (anything that won’t make a sound when it lands) in front of your pet to see if he follows the object. Remember that a dog with good vision in one eye will act normally, so it may not be possible to tell if vision is altered in the glaucomatous eye.
Veterinary care should include diagnostic care and subsequent treatment recommendations.
Diagnosis In-depth for Glaucoma in Dogs
A complete medical history and physical examination should be obtained by your veterinarian. Medical tests are needed to establish the diagnosis, exclude other disease and determine the impact of glaucoma on your pet.
Diagnostic tests specific to the eye (other tests to evaluate general health may/may not be necessary as well). A variety of specialized instruments are used for an eye exam including a transilluminator and a biomicroscope (also known as a slit lamp), as well as a direct and an indirect ophthalmoscope. The examination can help to answer some of the following important questions that will help determine the cause of glaucoma and the prognosis:
Is the pupil mobile?
Where is the lens?
How much inflammation is inside of the eye?
Are there any indications of a tumor or of trauma?
Do the retina and optic nerve appear healthy?
Other tests may include:
Tonometry may be used to measure the pressure inside of the eye (intraocular pressure, IOP). This test is very important and it has to be frequently repeated to determine how well treatments are working. There are several instruments used to check pressures, the most common of which are the Tonopen® and the schiotz tonometer. They are simple tests done in the exam room with just a drop of topical anesthetic on your pet’s eye.
Gonioscopy involves using a special lens placed on your pet’s eye so that the drainage angle can be viewed. This test is especially important when determining if glaucoma is primary (because of a narrow or malformed drainage angle). With some tumors that grow slowly in the eye, gonioscopy is used to periodically evaluate how close a tumor is to invading the drainage angle. Depending on the temperament of your pet, this test is generally done with just topical anesthetic so that your pet doesn’t feel the gonioscopic lens placed on the surface of the eye.
Treatment In-depth of Glaucoma in Dogs
Treatment for glaucoma can be broken down into medical and surgical care. Depending on the cause determined for glaucoma, different options are more or less appropriate.
Injectable and oral medications are used on an emergency basis to lower pressure, not on a long-term basis to control glaucoma: mannitol, glycerin (hyperosmotics).
Oral products to decrease the production of fluid in the eye: methazolamide, acetazolamide, dichlophenamide (carbonic anhydrase inhibitors).
Topical products to decrease the production of fluid in the eye: dorzolamide, brinzolamide (carbonic anhydrase inhibitors); timolol, betaxolol, levobunolol (beta blockers).
Topical products (from different drug classes) that try to open the drainage angle: phospholine iodide, ecothiophate, demarcarium bromide, pilocarpine, carbachol, latanoprost.
Oral and topical anti-inflammatories to decrease inflammation in the eye: prednisone, methylprednisone, dexamethasone (oral steroidals); carprofen, aspirin (oral nonsteroidals); prednisolone acetate/phosphate, betamethasone, dexamethasone (steroidal topicals); diclofenac, flurbiprofen, suprofen, indomethacin (non-steroidal topicals).
All above medications are generally used in combination with the dosing adjusted as needed.
Laser or Cryocycloablation – This uses a laser or freezing probe to kill some of the cells in the eye that are producing the fluid. This is appropriate for either a visual or a blind eye (a visual eye is treated less aggressively to kill just enough cells to decrease the pressure, but not to destroy too much of the inside of the eye).
Gonioimplant or Goniovalve – This involves placing a small tube in the eye to filter the excess fluid produced to the outside of the eye. It is generally used for a visual eye.
Enucleation – This is removal of the eye and results in eyelids that are permanently sewn shut. This is appropriate if the eye is blind. If there is a tumor inside of the eye, this is typically preferred because a pathologist can have the eye to determine what type of tumor it is.
Intraocular prosthesis – This is the removal of the inside of the eye, but the “shell” of the eye is left and a black silicone ball is placed inside. This is appropriate if the eye is blind. This can be used if there is a tumor inside of the eye, but further surgery could be necessary depending on the report from a pathologist.
Intravitreal injection – This involves injecting a medication into the eye that kills all of the fluid producing cells; frequently the eye shrinks down after this procedure.
There are many subtleties to be taken into consideration so all of the surgical options are not appropriate for any given case.
Follow-up Care for Dogs with Glaucoma
Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical and may involve the following:
Administer prescribed medication(s) as directed and be certain to alert your veterinarian if you are experiencing problems treating your pet. Repeated trips to your veterinarian are important in order to monitor the pressure within the eye and to make adjustments in medications. Do not stop glaucoma medications once they are started unless your veterinarian gives you instructions to do so.
Understand the medications that your dog is taking and what each one is used for. Ask your veterinarian about potential side effects to the drugs and how to monitor for those side effects. Also, ask your veterinarian about alternate plans should side effects be experienced by your dog.
Be aware that glaucoma may require long-term therapy and monitoring. Also be aware that all dogs that have experienced primary glaucoma in one eye are prone to the disease in the other eye. Ask your veterinarian about starting preventative therapy for the other eye.
Because glaucoma can be so rapidly devastating to an eye, it is important to have the dog evaluated immediately. An examination should not be delayed until the following day, or wait for the end of a weekend or holiday. Help should be sought immediately for any dog that has already been blinded by glaucoma in one eye, and who is exhibiting suspicious symptoms in the opposite (good) eye.