Glaucoma

OVERVIEW: 

 

Canine Glaucoma is one of the most common visual problems found in domestic dogs and is one of the leading causes of blindness in many breeds.  Glaucoma is defined as an imbalance of the fluid pressure within the eye, also known as intraocular pressure (IOP).  Within the eye, there is a fluid known as aqueous humor, a fluid that is entirely different from tears.  Aqueous humor is responsible for maintaining the proper shape and pressure of the inside of the eye.  Aqueous humor is constantly produced by the eye, a process sometimes referred to as “the faucet.”  In order to maintain the proper pressure, fluid must be regularly drained from the eye into the bloodstream.  The aqueous humor drains from the eye via a mesh-like structure known as the drainage angle or “the drain.”  Glaucoma is caused when there is some problem with the drainage angle which prevents it from properly releasing aqueous humor while at the same time “the faucet” continues to produce aqueous humor at the same rate.  The undrained aqueous humor begins to fill the eye, causing the eye to expand like a balloon and for the intraocular pressure to rise dramatically.  If glaucoma is not treated in time, the pressure within the eye can build up so much that it permanently damages some or all of the internal parts of the affected eye.  If the damage is severe enough, irreversible blindness may be the result.  Glaucoma varies greatly in severity and speed of onset.  In some dogs, deterioration due to glaucoma takes place over a period of weeks or months, while in others the condition results in permanent blindness in a matter of days or even hours.

 

There are two major categories of canine glaucoma, each of which is defined primarily by its cause.  Primary glaucoma, also known as inherited or hereditary glaucoma, is caused by genetics.  Dogs suffering from primary glaucoma have some inherent problem with their drainage angle, which eventually results in glaucoma.  There are between two and four major distinct types of primary glaucoma depending on the classification system used.  Open angle glaucoma, also known as wide angle glaucoma, is caused when the drainage angle is too wide.  Narrow angle glaucoma, also known as closed angle glaucoma, is caused when the drainage angle is too narrow or nearly entirely closed.  Although individual cases vary, open angle glaucoma generally progresses much slower than narrow angle glaucoma.  Goniodysgenesis is caused by a malformation of the tissue that allows the aqueous humor to drain.  Dogs suffering from goniodysgenesis often have drainage holes/mesh that are too small or too narrow and/or tissue strands and ligaments that are too short.  Pigmentary glaucoma is considerably rarer than the other forms of primary glaucoma.  Dogs with pigmentary glaucoma have an abundance of pigmented cells within the drainage angle and solera, an abundance which is so great that fluid drainage in impacted.  The inheritance mechanisms responsible for glaucoma are poorly understood, a situation made more severe because different types of glaucoma appear to be inherited differently and different breeds may inherit the same type of glaucoma in different ways.  Careful studies have shown how certain types of glaucoma are inherited in certain breeds such as open angle glaucoma in beagles (autosomal recessive) and narrow angle glaucoma in Welsh Springer Spaniels (autosomal dominant).

 

Secondary glaucoma occurs when the drainage angle is blocked due to a non-genetic factor.  There are numerous causes of secondary glaucoma, but most could be categorized as either accident/injury or illness/infection/other medical condition.  Depending on the cause of the secondary glaucoma, it is somewhat more likely to become serious rapidly.  It is very difficult to make generalizations about secondary glaucoma because each individual cause will impact the eye differently.

 

Luckily, glaucoma is very rarely life threatening.  It is, however, a very serious condition which can dramatically impact a dog’s life.  In the short term, glaucoma can be extremely painful and cause a great deal of misery as the eye fills with fluid.  In the long term, a dog may experience permanent vision loss or even complete blindness.  Dogs which lose vision in one eye are often able to adapt very well to their disability, and many seem hardly impacted at all.  Dogs which become permanently blind in both eyes are also capable of adapting very well, but the transition is much more challenging and substantially greater amounts of care are necessary.

 

Glaucoma normally impacts only one eye at a time, and most dogs initially only exhibit symptoms in the one impacted eye.  However, dogs which have developed glaucoma in one eye are much more likely to develop the condition in both eyes.  This is especially true with cases of primary glaucoma where the underlying genetic defect is likely to be the same in both eyes.  Every case is entirely different with some dogs developing glaucoma in the second eye days or weeks after the first, and some never developing it at all.  Veterinary studies have shown that a dog suffering from glaucoma in one eye will develop glaucoma in the second eye an average of eight months later if no preventative measures are taken.  If proper preventative measures are taken with the second eye, this average is extended to 31 months later.

 

RISK FACTORS: 

 

The following factors have either been shown to or are widely believed to increase a dog’s chances of developing glaucoma:

 

  • Breed – All forms of glaucoma have been identified in nearly all dog breeds, and are especially common in Spitz-type dogs.  However, certain forms are more commonly seen in certain breeds.  Some of the breeds most commonly affected by open angle glaucoma include the Beagle, Boston Terrier, Miniature and Schnauzer.  Among the breeds most commonly affected by narrow angle glaucoma are the Alaskan Malamute, Chow Chow, Dalmatian, Great Dane, Smooth Fox Terrier, Standard Poodle, and the Welsh Springer Spaniel.  Among the breeds most commonly diagnosed with Goniodysgenesis are the Bouvier des Flandres, Chihuahua, and Dandie Dinmont Terrier.  The much rarer pigmentary glaucoma is largely limited to the Cairn Terrier.  Several breeds are highly susceptible to multiple or all forms of canine glaucoma including the American Cocker Spaniel, English Cocker Spaniel, Basset Hound, Wire Fox Terrier, Miniature Poodle, Toy Poodle, Siberian Husky, Norwegian Elkhound, and Samoyed.
  • Genetics – Because most cases of glaucoma are caused by genetics, dogs whose close relatives have been diagnosed with glaucoma are much more likely to develop the condition.
  • Prior Cases of Glaucoma – Dogs which have already had primary glaucoma in one eye are very likely, if not nearly guaranteed to develop glaucoma in the second eye.  The likelihood of dogs which had secondary glaucoma in one eye developing it in the other varies dramatically depending on the underlying cause of the glaucoma.
  • Age – Glaucoma can strike dogs of any age, especially secondary glaucoma.  However, dogs over the age of three are at substantially greater risk of developing glaucoma, and the older the dog is the more likely it is to experience glaucoma.

 

SIGNS & SYMPTOMS: 

 

Unfortunately for dogs and their owners, the signs and symptoms of glaucoma are nearly imperceptible when the condition is in its beginning stages.  Most owners, even the most vigilant, are completely unaware that anything is wrong with their pet’s eye until the glaucoma has progressed to an advanced stage.  In fact, most general veterinary practitioners will not notice the disease in its early stages.  The signs and symptoms of advanced glaucoma are very apparent and obvious, but by the time they appear it is usually too late to save the dog’s vision.  Part of the problem is that dogs, like all animals, have a natural urge to avoid showing any signs of pain or weakness.  Most dogs are more than capable of using their other eye to see and may not demonstrate any visual loss at all.

 

Although most cases of glaucoma go unnoticed in the early stages, there are a few signs which may appear.  The dog may rub its eye as if it is irritated or in pain, this rubbing may be either occasional or frequent.  Some dogs may also exhibit a reluctance to open their eyes when in direct sunlight, and some may even seem reluctant to go outside altogether.  Other potential warning signs include repetitive blinking, excessive squinting, and lethargy.  Some dogs may develop redness and/or cloudiness in the eyes at early stages, but these are more commonly seen in advanced glaucoma.

 

Advanced glaucoma is very immediately obvious.  The eyes of affected dogs often turn bright red and bloodshot.  The eye also enlarges, often to a size significantly larger than normal.  The shape of the eye can also change, and many become bulging.  The entire eye gradually clouds over, eventually becoming barely recognizable.  The most immediately obvious sign to many pet owners is color change.  The many changes occurring within the eye as a result of glaucoma often make an affected eye appear green, blue, grey, or light brown.  Some dogs may also be unable to fully close their eyes as a result of the condition because their eyelids cannot fit over the enlarged eye.

 

Dogs suffering from glaucoma also frequently exhibit a number of behavioral changes in addition to the eye rubbing mentioned earlier which worsen as the condition progresses.  As the pain progresses, many dogs exhibit an aversion to being pet or touched on the face and head.  Many dogs exhibit signs of being in pain, such as whimpering, whining, and reluctance to move.  As a dog’s vision in increasingly impacted, it may begin to bump into furniture or other obstacles, especially if they are only visible from one side of the body.  The dog may not notice things it usually would, for example a squirrel running or a ball being thrown.  Because they are no longer as capable of sensing the world around them, many dogs begin to bark excessively and become nervous, over reactive to sounds, snappy, and even aggressive.  The dog is usually especially reactive to sounds from the side which it is losing vision.

 

DIAGNOSIS & TESTS: 

 

Although every veterinarian will operate slightly differently, most cases of glaucoma are diagnosed after a multiple (usually five or six) step process.  First, the veterinarian will consider a number of factors such as the dog’s breed, age, and symptoms which impact the likelihood that the animal is suffering from glaucoma.  Next, the veterinarian will perform a visual examination of the dog’s eye.  In cases of advanced glaucoma, the symptoms such as redness, cloudiness, and enlargement will be immediately apparent, but in cases of early stage glaucoma the signs may not be visually apparent.  These cursory evaluations are then followed up with several common tests.  Many general veterinary practitioners do not have the necessary expertise or equipment to perform some of these tests.  For this reason, where glaucoma is suspected, especially if it is in the early stages, many veterinarians will refer their clients to a veterinary ophthalmology specialist, or at least a major veterinary hospital.  Veterinarians always want to move as quickly as possible whenever glaucoma is thought to be a possibility, both because the condition can worsen so rapidly and due to its potentially severe effects.

 

The most basic test to determine whether a dog has glaucoma is known as tonometry.  In order to conduct tonometry, anesthetic drops are placed in the dog’s eye and the intraocular pressure is measured using an instrument known as a tonometer.  There are three types of tonometer currently available, digital, indentation, and applanation.  Most veterinarians find applanation tonometers to be the most reliable but individual preferences vary.  Although every individual dog has a slightly different normal intraocular pressure, most are in the range of 15 to 20 mm Hg.  A reading higher than 25 mm Hg is usually considered to indicate glaucoma, although some veterinarians claim that it is actually 30 mm Hg.  Intraocular pressure above 50 mm Hg indicates that the dog is in serious danger of permanent eye damage and vision loss, if they have not occurred already.

 

If tonometry determines that the Intraocular pressure is abnormally high (and often if it does not) additional tests will be performed.  Gonioscopy tests the drainage angle of the eye.  Gonioscopy can not only help diagnose glaucoma, but can also tell if the glaucoma is open angle or narrow angle.  Opthalmoscopy is a more advanced set of tests designed to carefully examine the various parts of the eye, especially the retina and optic nerve.  Although opthalmoscopy is useful in diagnosing glaucoma, it is used primarily to determine the extent of the damage caused by the condition.  A number of additional tests may be recommended by veterinarians depending on the circumstances of each individual case, including x-rays and 3-D imaging.

 

Once the dog has been diagnosed with glaucoma, the veterinarian will often order additional tests to determine the cause of the glaucoma.  For example, various viral and bacterial cultures may be ordered to determine whether the glaucoma is the result of an infection or disease.  Brain scans may be necessary to see if head trauma is the underlying cause.  It is very important for a veterinarian to determine the cause of glaucoma in order to determine the proper treatment. 

 

CONVENTIONAL TREATMENT & MANAGEMENT: 

 

There are literally hundreds of different treatment and management options available for canine glaucoma, and every individual case will require its own unique treatment.  To begin with, treatment options are heavily determined by whether the glaucoma is primary or secondary.  In cases of secondary glaucoma, veterinarians usually prescribe a regimen of medications to treat the glaucoma temporarily.  The exact products recommended will be determined by the progression of the condition, the veterinarian’s personal preference, and the expected necessary duration.  There are currently dozens of treatments available to temporarily treat canine glaucoma, and more are being developed all the time.  While these treatments for the glaucoma are being given, the underlying cause of the glaucoma will attempt to be cured or resolved.  The treatment necessary for these underlying conditions varies tremendously, for example an infection may require an antibiotic regimen but head trauma may require neural surgery.  Provided that the underlying cause of the secondary glaucoma is resolved, the prognosis for glaucoma recovery is usually much better than that of primary glaucoma and often does not require surgical repair.  Additionally, dogs with secondary glaucoma are much less likely to develop glaucoma in their other eye than dogs with primary glaucoma, meaning that treatment is likely to cease after the underlying condition has been resolved.

 

Cases of primary glaucoma are often much more challenging to treat than cases of secondary glaucoma and often have less satisfactory results.  Ideally, the glaucoma will be detected at an early enough stage that immediate surgery is not necessary.  Veterinarians will usually prescribe a similar set of treatments as they would for a dog suffering from secondary glaucoma.  In a small minority of cases, these treatments will be sufficient to permanently stave off the development of advanced glaucoma and vision loss, although they essentially never cure the glaucoma.  Because these treatments only “hold the glaucoma back” rather than curing it, most will have to be provided for the rest of the dog’s life, often a very expensive proposition.  Although preventative treatments often prevent glaucoma from advancing for months or even years, eventually most dogs suffering from primary glaucoma will eventually see their condition substantially worsen.  Because wide angle glaucoma tends to progress much more slowly than narrow angle glaucoma, treatments are generally considerably more effective treating it.

 

Once a case of primary glaucoma has advanced or a case of secondary glaucoma is not resolved once the underlying cause is cured, surgery is essentially the only option.  There are a number of different types of glaucoma surgeries available, and which one is selected depends heavily on the type and progression of the glaucoma.  In general, these surgeries have four goals: reduce aqueous humor production within the eye, increase aqueous humor drainage from the eye, reduce intraocular pressure, and prevent or reduce potential long-term damage.

 

For dogs that have already experienced permanent vision loss, there are basically only two available options.  The most commonly used is enucleation, a surgery which removes the entire eyeball.  After the eyeball has been removed, the resulting hole may either be covered with skin and hair or filled with a prosthetic eye, usually made out of glass.  Most owners choose the former option because it is cheaper and requires less long term maintenance.  Those who choose the second do so because they find the appearance less disturbing or unsettling, not for any medical or emotional benefits to the dog.  For owners who do not want to have enucleation performed, there are injections available which will permanently kill aqueous humor producing cells in the eye.  Once those cells have been killed, the pressure level in the eye will gradually decrease.

 

There are a number of additional treatments available for dogs that have not yet experienced permanent vision loss, many of which are frequently used in conjunction with each other.  One of the fastest growing is laser surgery, specifically endolaser cyclophotocoagulation (ECPC) laser surgery.  In ECPC laser surgery, a small laser probe is inserted into the eye.  The laser beam selectively destroys some of the cells which produce aqueous humor.  ECPC is more of a preventative surgery for dogs that have not responded to non-surgical treatments than a cure, but can substantially reduce intraocular pressure over time.  Because ECPC require the lens of the eye to be removed, an artificial one is inserted after the surgery is complete.  ECPC is a very complex and expensive procedure, and only a few veterinary ophthalmologists are currently performing it.

 

Other common surgeries for canine glaucoma fall into one of two categories, intraocular evisceration and implantation or shunt placement.  In intraocular evisceration and implantation, the inner contents of the eye are removed and replaced with implants while the outer portions of the eye remain natural.  Intraocular evisceration and implantation is usually a last resort used in dogs with more advanced glaucoma that have already begun to experience vision loss.  Shunts are small implants which increase the amount of aqueous humor that is drained from the eye.  There are several different types and brands of shunts currently available for glaucoma treatment most of which rely on tubes, valves, or biomaterial to function.  The type of shunt chosen will depend on the type of glaucoma, its progression, and the veterinarian’s personal preference.  As is the case with laser surgery, the placement of shunts is primarily a preventative measure for dogs which have not responded to other treatment options, and will not necessarily cure the glaucoma.

 

The prognosis for dogs undergoing surgery for glaucoma varies tremendously on a case by case basis.  Most dogs will see a substantial delay in vision loss, often months or years.  However, in most cases even the most successful surgery will only delay the inevitable, not prevent it entirely.

 

Because glaucoma usually affects both eyes, especially in cases of primary glaucoma, a dog which has been diagnosed with glaucoma in one eye will usually have to receive aggressive preventative measures for its other eye, including all previously mentioned options.  Such preventative measures are especially necessary because by the time glaucoma is diagnosed in the first eye it is often too late to save it.

 

POTENTIAL COMPLICATIONS: 

 

The major potential complication from glaucoma is vision loss.  This loss starts off with mild vision loss but often progresses to full blindness.  Depending on the severity of the glaucoma and how quickly it was diagnosed, this vision loss may either be temporary or permanent.  Other potential complications from glaucoma include headaches, injury from vision loss, and eye injury due to a dog self-mutilating itself in an attempt to relieve the pain.

 

There are many potential complications from glaucoma treatments.  All medicinal treatments have potential side effects, especially when multiple medications are working in concert with each other.  Veterinarians should be carefully consulted on the side effects of all glaucoma medications prior to use.  The surgical treatments for canine glaucoma have many potential risks as well.  Some dogs are allergic to anesthesia, and may experience difficulty breathing, heart problems, anabolic shock, and even death when put under.  There is always a risk that a dog may bleed to death when on the operating table, particularly if it has an undiagnosed blood disorder such as Von Willebrand’s disease.  There is also a risk that another body part will be damaged as a result of surgery.  Because glaucoma surgeries are limited almost entirely to the eyes, such procedures have fewer risks than many others.  Also because Glaucoma surgeries focus on the eyes, they can severely impact vision.  In some cases, even where the surgery was carefully and properly conducted, the dog may experience permanent vision loss or even blindness.  In the case of shunt placement, sometimes a thick tissue may grow over the shunts which prevents aqueous humor drainage, ironically worsening and hastening the glaucoma.

 

HOLISTIC REMEDIES: 

 

Unfortunately, there are no holistic remedies which can cure glaucoma.  This is because glaucoma is caused by a structural problem within the dog’s eye which can only be helped by making physical changes to the inside of the eye via surgery.  There are, however, a number of holistic remedies available which may be useful in relieving the symptoms of glaucoma and potentially slowing its progression.  Many of these treatments can be used to relieve a dog’s pain and discomfort, and also to delay surgery or vision loss.  Holistic treatments are least effective when the dog has already lost vision, and surgery has become essentially the only option.  Because any holistic treatment may interact in a negative way with conventional medical treatments, all should be discussed with the dog’s veterinarian prior to use.

 

Many of the herbs used to holistically treat glaucoma have strong anti-inflammatory properties such as Rosemary (Rosmarinus officinalis), Chelidonium majus, and Meadow Sweet (Filipendula ulmaria).  Such herbs are thought to reduce swelling within the eye and therefore reduce pain and discomfort.  Some holistic treatments are designed to strengthen the eye and/or increase vision, helping to both ward off and offset vision loss.  Among the most commonly suggested of such treatments include Burdock (Arctium sp.), Bilberry (Vacciuium myrtalis), ZincZinc is an essential mineral believed to possess antioxidant properties, which may protect against accelerated aging of the skin and muscles of the body; studies differ as to its effectiveness. In pet foods is considered important in helping to support healthy skin, hair and mucous membranes. Zinc also helps speed up the healing process after an injury. It has antioxidant properties and is also beneficial to the body's immune system. Zinc also helps stimulate the action of more than 100 enzymes, and helps to stimulate the sense of smell, synthesize DNA and RNA, and promotes normal growth and development., Lutein, mixed Carotenoids, Vitamin A, Vitamin C, and Vitamin E.  Other more generic holistic treatments thought to help with canine glaucoma include Quercetin, Alpha Lipoic AcidAlso known as the “universal antioxidant,” Alpha lipoic acid has many important functions, including providing the body with defense against free radical damage and helps to convert glucose (blood sugar) into energy. , and Grape Seed Extract.

 

PREVENTION & HELPFUL TIPS: 

 

When it comes to prevention of canine glaucoma, prevention must be divided into two types, prevention of the condition and prevention of the condition progressing to an advanced stage and the visual loss that accompanies it.  It is possible for owners to prevent many cases of secondary glaucoma entirely.  Keeping a dog safe from accidents and injury can prevent some cases of secondary glaucoma, as will rapid medical treatment of all potential infections, especially eye infections.  Because primary glaucoma is caused by a genetic malformation of the interior parts of the eye which is present from birth, it is essentially not possible to prevent.  There are a number of possibilities to prevent the advancement of glaucoma and the vision loss that results, both in cases of secondary and primary glaucoma.  Most of these preventative measures have already been described in the sections for Conventional Treatment and Management and Holistic Remedies.  Although many of these options can delay the worst effects of glaucoma for months and even years, they usually cannot prevent the condition from developing entirely.

 

Although the exact inheritance mechanisms behind most forms of glaucoma in most breeds are still poorly understood, it is universally agreed that primary glaucoma is caused by genetics.  For this reason, it is highly recommended that any dogs suffering from primary glaucoma, along with their parents, siblings, and offspring, not be bred and ideally fixed.  The Canine Eye Registration Foundation (CERF) keeps records of dogs which have been diagnosed with glaucoma along with providing a number of other resources for breeders, owners, and fanciers.  Such breeding precautions may not be necessary for cases of secondary glaucoma, especially ones caused by accident or infectious disease.

 

Not all veterinarians are familiar with the likelihood of glaucoma developing in all breeds, especially rare ones.  For this reason, owners of breeds with a high likelihood of developing glaucoma should notify their veterinarian.

 

Because glaucoma can advance very rapidly and because it can cause permanent blindness, it is highly advisable for owners who suspect that something may be wrong with their dog’s vision to see a veterinarian immediately.  Because the early signs of canine glaucoma are often unnoticed even by highly trained veterinarians, this condition can be very difficult to diagnose and treat in a timely fashion, especially in the first eye which has been impacted.