Glaucoma (Canine)
| PrintGlaucoma is a condition in which the pressure within the eye becomes elevated. It is often very painful and is a leading cause of blindness in dogs. Glaucoma may be a primary disorder or the result of other disease within the eye.
Common name: Glaucoma, elevated pressure in the eye
Scientific name:Glaucoma, diagnosis
Diagnosis
Signalment
Primary glaucoma is likely an inherited disease and is more common in the following breeds: 1) Narrow angle glaucoma – American cocker spaniel, Basset hound, Toy Poodle, Standard poodle, Siberian husky, Chow chow, Samoyed, and mixed breeds 2) Open angle glaucoma -- American cocker spaniel, Boston terrier, Beagle, Basset hound, Miniature schnauzer, and mixed breeds. Narrow angle glaucoma is much more common than open angle glaucoma and it is also twice as common in female dogs as in males. Primary glaucoma may occur at any age but predominantly occurs during middle age.
Secondary glaucoma may occur more commonly in terrier breeds, American cocker spaniel, toy and miniature poodle, and many others including mixed breeds. There is no apparent sex predilection in dogs with secondary glaucoma.
Incidence/prevalence
Glaucoma is one of the most common causes of blindness in dogs.
Geographic distribution
There is no known geographic distribution.
Clinical signs (primary most to least frequent, scientific term, synonyms)
Blepharospasm (squinting, holding eyelids closed, indicative of pain in the eye), acute vision loss, episcleral injection (redness), corneal edema (thickened, cloudy appearance to the cornea), pupil dilated and fixed (unresponsive to light)
Clinical signs (secondary most to least frequent, scientific term, synonyms)Altered behavior secondary to pain (such as vocalizing, not eating, lethargy, etc.), Buphthalmus (enlargement of the globe of the eye) -- chronic glaucoma.
Cause (scientific, common term)
Genetic basis (inherited) primary glaucoma, lens luxation or subluxation (lens has moved from its normal position in the eye), anterior uveitis (inflammation in the iris, ciliary body and or choroid), trauma (direct damage to the eye), cataract (opacity in the lens), intraocular neoplasia (tumor within the eye).
Organ system affected (most to least affected)
Eye.
Diagnostic tests
Ophthalmic examination, tonometry (measurement of intraocular pressure), gonioscopy (evaluation of the filtration angles in the eye), blood chemistry/Complete blood count (screen for systemic disease if secondary glaucoma), electroretinography (ERG), may help determine extent of irreversible vision loss, ocular ultrasound, may help determine position of related structures within the eye to assess prognosis for restoration of vision.
Differential Diagnosis
Uveitis (eye is painful but intraocular pressure is usually lower than normal), conjunctivitis (eye is painful and red, intraocular pressure is not high), blindness due to other causes, other causes of pain or redness such as trauma, Neoplasia (cancer), although often not painful.
Overview
Glaucoma is a condition in which the pressure within the eye becomes elevated. It is often very painful and is a leading cause of blindness in dogs. Glaucoma may be a primary disorder or secondary (the result of other disease within the eye).
In the normal eye, a fluid called aqueous humor is produced by a portion of the eye known as the ciliary body. Normal aqueous humor flow within the eye maintains a stable intraocular pressure (IOP) and also carries nutrients to (and waste products from) those portions of the eye that do not contain blood vessels, such as the lens and the cornea. Aqueous humor leaves the anterior chamber of the eye through the filtration angle. When the outflow of aqueous humor is obstructed, fluid builds up and leads to an elevated IOP. Normal IOP in dogs ranges from 15 to 25 mmHg.
Primary glaucoma can be classified as narrow angle (in which the filtration angle is narrow and does not allow adequate outflow of aqueous humor), open angle (filtration angle appears normal but outflow is likely obstructed by a deeper structure), or goniodysgenesis (in which the filtration angle has not developed normally). Primary glaucoma is often a bilateral disease (both eyes are affected, although often one at a time) and is likely inherited.
Secondary glaucoma occurs as the result of other intraocular disease, such as anterior uveitis (inflammation of the iris, ciliary body and or choroid), lens luxation or subluxation (the lens has moved out of its normal position in the eye), trauma, cataract, or neoplasia (cancer).
Glaucoma may be acute (a sudden rapid rise in IOP with no previous signs) or chronic (progressive but not necessarily apparent immediately). Although patients with chronic glaucoma may not have the pronounced sudden onset of signs, they are still likely painful and develop blindness.
Vision loss may occur more quickly if there is a sudden profound rise in IOP versus a gradual increase. Blindness results when the IOP leads to damage of the cells in the back of the eye that are responsible for vision or direct damage to portions of the optic nerve.
Treatment
Home Care
Initially, dogs with glaucoma may not be able to be managed at home until IOP is significantly reduced. Once the pressure is stable, the patient may be managed at home with topical (eye drops or ointment) and possibly systemic medications. Patients should be monitored closely for signs of pain (squinting eye, behavioral changes related to pain), vision loss, or redness. The other eye should be monitored closely as well.
Professional Care
Medical therapy must be initiated right away before permanent blindness occurs (irreversible visual impairment may result in 12-24 hours if the IOP is greater than 60 mmHg). Goals of medical therapy are to prevent vision loss and make the patient comfortable (reduce pain). A dog may be seen by an emergency veterinarian for treatment. However, whenever possible, patients with glaucoma should be managed by a veterinary ophthalmologist, which is a specialist that is a Diplomate of the American College of Veterinary Ophthalmologists. Medications to treat glaucoma are given to reduce pressure in the eye, improve drainage of aqueous humor, and reduce pain. Surgical intervention may be necessary to preserve vision and restore comfort.
Action
Acute glaucoma is a medical emergency. Dogs with signs of acute glaucoma should be seen by a veterinarian immediately. A veterinary ophthalmologist will devise an appropriate treatment plan. Once glaucoma has been diagnosed, treatment is long term. It is critical that patients with glaucoma are rechecked by a veterinarian at regular intervals to monitor intraocular pressure in both eyes.
Outcome
Although most primary glaucoma initially presents with only one affected eye, the other eye will also likely become affected in the future without medical therapy. With medical therapy alone, many patients with glaucoma become blind. Surgical intervention may help maintain vision for a longer period of time. Dogs with chronic glaucoma that have permanent blindness and severe pain should have the affected eye enucleated (removed) or placement of an intraocular prosthesis. The prognosis for dogs with secondary glaucoma depends on the underlying cause and extent of damage in the eye.
References/Additional Readings
Miller, Paul E. Glaucoma. In Slatter, Douglas, ed. Textbook of Small Animal Surgery. Philadelphia: Saunders, 2003, 1454, 1477.
Narfström, Kristina, Ellen Bjerkås, and Björn Ekesten. Visual Impairment. In Peiffer, Robert L Jr. and Peterson-Jones, Simon M, eds. Small Animal Ophthalmology. Philadelphia: Saunders, 1999, 85, 165.
Renwick, Peter W. and Peterson-Jones, Simon M. Orbital and Ocular Pain. In Peiffer, Robert L Jr. and Peterson-Jones, Simon M, eds. Small Animal Ophthalmology. Philadelphia: Saunders, 1999, 167, 196.
Author
Michelle Kazdin, VMD
Editor
Sharon M. Gwaltney-Brant, DVM, PhD, DABT, DABT
Please note that PetVet should only be used as a guide and in no way should be substituted for licensed veterinary care.
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