Glaucoma is a serious disorder characterized by fluid build-up inside of the eye. It causes increased intraocular pressure, vision impairment and, if untreated, blindness. Glaucoma can be primary or secondary. Primary glaucoma is a genetic disease that most commonly affects certain breeds. It typically is progressive and eventually causes blindness in both eyes. Secondary glaucoma results from some other primary eye disease or damage. Either type of glaucoma can be acute or chronic in onset.
Causes of Glaucoma
The normal eye is filled with a fluid called aqueous humor. The amount of aqueous humor normally is carefully regulated to keep the eyeball in its proper shape. This happens from a very slow, but fairly continuous, exchange of fluid between the inner eye chambers and the blood in systemic circulation. This balance is disturbed in dogs with glaucoma, because aqueous humor is being produced faster than it can be removed, causing pressure to build up. Without treatment, the sustained elevated intraocular pressure will damage the retina and ultimately cause degenerative changes in the optic nerve as well, resulting in blindness.
Prevention of Canine Glaucoma
There is no guaranteed way to prevent glaucoma in dogs. However, routine eye examinations can identify small changes in intraocular pressure, which can allow meaningful medical management before full-stage glaucoma develops. Dogs with glaucoma in one eye should be watched closely for development of the disease in the other eye. Most authorities recommend that dogs with primary glaucoma not be used in a breeding program. Acute-onset gluacoma due to trauma or some other eye disorder is a true medical emergency that requires immediate veterinary attention to reduce the pressure inside of the eye, which usually can be accomplished by use of intravenous medications.
Glaucoma is normally not life-threatening, but it definitely can adversely affect a dog's quality of life. The prognosis for dogs suffering from glaucoma is variable. Most dogs will become blind, despite medical and/or surgical intervention. There is now some evidence that repeated forceful pulling on a dog's neck collar increases the fluid pressure inside their eyes. Dogs predisposed to glaucoma or who have already developed glaucoma in one eye may do better walked on a harness rather than a collar.
Glaucoma refers to elevated pressure inside the eye that causes vision impairment and, if left untreated, blindness due to degenerative damage to the retina and optic nerve. The clinical signs of canine glaucoma are fairly nonspecific and change over time depending on the stage of the disease. Many owners do not realize that their dog is suffering from glaucoma until the condition has progressed to an advanced stage. However, subtle changes in the appearance of the eyes can provide an early warning that glaucoma is present.
Symptoms of Glaucoma in Dogs
Owners may notice one or more of the following signs of glaucoma in their canine companions:
Abnormal ocular discharge
Stumbling over or bumping into normal objects
Behavioral changes associated with pain
Lack of appetite (anorexia)
Bulging eyes (buphthalmia)
Large (dilated) pupils
Pawing at or rubbing the eyes or face
Aversion to being petted or touched on the face or around the eyes
Extreme sensitivity to or avoidance of bright or direct light (photosensitivity)
most cases, glaucoma appears first in one eye, and a short time later appears in the other. Other early signs of glaucoma involve changes to the appearance of the pupil, which may be dilated (larger than usual) and may not contract quickly when exposed to light. Vision loss normally is not noticed by pet owners. However, if a dog's vision has been dramatically affected by the disease, owners may notice that their dog stumbles over objects in its path, barks more often than usual or bumps into the corners of walls and doorways. In advanced stages, glaucoma causes the affected eye(s) to bulge, called globe enlargement, "buphthalmos" or "hydrophthalmos," and the eyes may take on a greenish sheen. Treatment is necessary to prevent permanent eye damage, pain and blindness.
Dogs at Increased Risk
There is no particular age or gender predisposition to the development of glaucoma in dogs. While it can occur in any breed, certain breeds are predisposed to this condition, including some spaniels (the American and English Cocker Spaniel, English and Welsh Springer Spaniel), Basset Bound, Beagle, Chow Chow, Chinese Shar-Pei, many terriers (including the Boston, Wire Fox, Cairn, Manchester, Dandie Dinmont, Norfolk, Norwich, Scottish, West Highland White and Parsons Jack Russell), some arctic breeds (the Norwegian Elkhound, Siberian Husky, Malamute, Akita and Samoyed), retrievers (Flat-Coated and Golden), Bouvier des Flandres, Maltese, Shih-Tzu and Miniature Poodle. Many other breeds have been reported to suffer from primary or secondary glaucoma, as well. Dogs with glaucoma often exhibit behavioral changes attributable to pain.
Glaucoma in dogs is diagnosed by conducting a thorough physical examination and an ophthalmic inspection of the eyes. Specific instruments are used to assess intraocular pressure and, if necessary, advanced diagnostic techniques can be used to determine the health of or extent of damage to the eyes.
How Canine Glaucoma is Diagnosed
At the outset, glaucoma must be differentiated from other causes of non-specific eye redness and irritation, including conjunctivitis, anterior uveitis, ectropion and entropion, among many others. This is accomplished by a thorough ophthalmic examination, during which the veterinarian looks closely at the external and internal structures of both eyes, even if only one appears affected. Simple vision tests also may be conducted to determine whether a dog's sight is impaired. These tests usually involve hand movements to assess peripheral vision, and tossing cotton balls around the room to assess the dog's ability to follow subtle movements.
Assessment of internal eye pressure (intraocular pressure) using a tonometer is essential for the diagnosis and clinical management of glaucoma and is the single most important diagnostic tool in a veterinarian's arsenal. At present, there are three available types of tonometry: digital, indentation and applanation. Of these, most experts find applanation tonometry to be the most reliable, although personal preferences among veterinarians will vary. Intraocular pressure tends to be higher in early morning and lower in early evening; several reproducible tonometer readings should be taken for a conclusive diagnosis of glaucoma.
Advanced testing, normally conducted upon referral to a veterinary eye specialist, can include radiographic (X-ray) or ultrasonic imaging to look for damage inside the eye. Blood tests can be performed to identify possible underlying infectious or inflammatory disease. Gonioscopy (evaluation of the angle at which the intraocular fluid drains from the eyes), and possibly an electroretinogram (ERG), are also available to help the veterinary ophthalmologist determine whether a dog's affected eyes are capable of medical or surgical vision restoration.
Most of these diagnostic tests are noninvasive and fairly quick. They are best conducted with only light restraint. They are painless, because topical anesthetic drops are applied to numb the dog's eyes before the examination begins.
Treating options for glaucoma in dogs vary based upon the underlying cause of the condition. Treatment normally involves application of topical eye medications, administration of systemic medication and eventually surgery. This progressive condition may occur in one or both eyes, and immediate treatment is necessary to prevent permanent eye damage, pain and blindness. The goals of glaucoma therapy are to lower intraocular pressure of affected eyes in order to maintain the dog's vision as long as possible, and also to eliminate ocular pain.
Regardless of the cause, most cases of canine glaucoma are initially treated with some combination of topical and systemic medications designed to decrease intraocular pressure. A number of prescription drugs are available to dehydrate the aqueous humor (the fluid inside of the eye), reduce the production of aqueous humor and/or increase the drainage of aqueous humor from the eye. Topical corticosteroids also may be used, provided that corneal ulcers are not present (because in addition to their anti-inflammatory effects, steroids tend to delay tissue healing).
If only one eye is affected by glaucoma, the other eye (called the "fellow eye") can be treated prophylactically; this seems to delay the onset of glaucoma in the fellow eye for several months, or even longer. New medications are always in development, and only a veterinarian can determine which of the available drugs to use in any given situation. In all cases, dogs with glaucoma should be reevaluated regularly in order to track intraocular pressure and make necessary adjustments in medication. Medical treatment is usually life-long and can be quite expensive. Unfortunately, with drug therapy alone, most dogs with primary glaucoma will eventually go blind.
A number of surgical procedures are available to help manage glaucoma if medical management is unsuccessful. The goals of glaucoma surgery are to increase the outflow of aqueous humor, decrease its production, maintain vision as long as possible and resolve ocular pain. Surgical options include placement of small implants (called shunts) into the eye and/or using laser therapy (called cyclophotocoagulation) to promote fluid drainage, reduce fluid production, prolong vision and reduce pain. Another procedure involves the injection of certain drugs into the eye or using cryosurgery (freezing) to damage or destroy the cells that produce aqueous humor. Surgical removal of the lens in affected eyes is also possible.
Unfortunately, in most cases, these surgical procedures only slow the progression of glaucoma rather than curing it. Affected eyes often develop irreversible scarring and vision loss, despite surgery performed by a skilled veterinarian. Once glaucoma progresses to blindness, or if medical pain management is unsuccessful, there are several surgical salvage options. The globe (eyeball) can be surgically removed, which is called enucleation. It can also be surgically eviscerated, which involves removing the contents of the eyeball while leaving the tough, usually white outer part of the globe, called the sclera, intact. These procedures will remove the source of the severe and chronic pain that typically accompanies end-stage glaucoma, although they of course will not restore vision. Prosthetic implants are available as well, for a result that is cosmetically acceptable to owners.
The success of any glaucoma treatment depends heavily upon how early the condition is diagnosed, and whether it is primary or secondary to another problem. The prognosis for the first eye affected by glaucoma is normally poor, regardless of the cause or treatment protocol, because by the time the disease is diagnosed, it usually is advanced and unresponsive to medical therapy. Preventative (prophylactic) medical treatment of the fellow eye can help delay the onset of glaucoma for many months.