Glaucoma in Dogs

Glaucoma is the condition of increased pressure in the eye. Eye pressure is normally regulated by fluid flowing into and out of the eye at a balanced rate. If too much fluid is made or too little fluid is drained, the pressure in the eye increases, causing damage to the retina and optic nerve. Glaucoma can be painful and approximately 40 percent of cases lead to blindness within one year. If treatment is not started within hours of pressure increase, vision will likely be lost. Glaucoma is the elevation of pressure inside the eye, known as intraocular pressure (IOP) beyond a specific point at which vision is compromised or is no longer possible. Glaucoma is a frequent cause of blindness in both humans and animals.

Symptoms of glaucoma should be treated as an emergency as vision can be lost within hours of disease signs. Glaucoma usually begins in one eye. 50 percent of cases spread to the other eye if left untreated.

Symptoms may include one or more of the following:

• Pupils of eyes different sizes
• Mild to severe eye pain (rubbing eye on the floor or with paw)
• Appearance of vessels in the white of the eye
• Redness of the eye
• Cloudy cornea
• Fluttering eye lid
• Squinting
• Tearing
• Appetite loss and anti-social behavior (due to pain)
• Light avoidance
• Weak blink response
• No response of pupil to light
• Vision problems (bumping into objects, difficulty finding toys, walking gingerly)
• Bulging swollen eye

Types

There are two forms of glaucoma in dogs:

• Primary Glaucoma – The fluid flow rate into or out of the eye is abnormal resulting in an increase in eye pressure.
• Secondary Glaucoma – A separate condition causes intraocular fluid drainage to be slowed or blocked, resulting in increased pressure. Twice as common as primary glaucoma.

Intraocular pressure is measured using a tonometer:

• Normal Intraocular Pressure – 15-25mmHg
• Primary Glaucoma – 25-30mmHg
• Secondary Glaucoma – 10-30mmHg

• Primary Glaucoma – Caused by genetic predisposition. Usually appears at or after 2 years of age. Genetically predisposed breeds include (but are not limited to) the basset hound, beagle, chihuahua, chow, cocker spaniel, dachshund, maltese, miniature poodle, samoyed and siberian husky.
• Secondary Glaucoma – Caused by infection, inflammation, injury, lens luxation, or tumor.

As irreversible eye damage and vision loss can occur within hours of symptoms, if any one of the symptoms are noted, visit your veterinarian immediately. Your vet will want to know onset of symptoms and any history of trauma or behavioral patterns associated with pain or vision loss. He will perform an ophthalmologic exam and may choose to treat your pet in the clinic or may refer you to veterinary ophthalmologist.

Tonometry

Intraocular pressure is measured with a tonometer. A drop of anesthetic may be put on the eye first. One type of tonometer blows a puff of air on the eye and measures the indentation. Another type presses a small plastic disk against the eyeball to measure pressure. The Mueller method uses an electronic tonometer.

In sudden glaucoma, the pupil has a sluggish response to light, the blink response is weak or absent, the cornea is swollen or cloudy, the eye is red, inflamed and tearing, and the pet may be squinting.

In chronic glaucoma, the pupil has no response to light and the blink response is absent. The cornea is cloudy and the eye is red and inflamed. Tearing is possible and vessels are seen on the cornea. The eye is often enlarged.

X-ray

Your veterinarian may want to rule out the presence of an eye abscess, injury or tumor. An x-ray or ultrasound will allow the space around the eye to be visualized.

Treatment depends on cause and severity of the glaucoma. The goal of treatment is to restore normal eye pressure (by decreasing fluid production and/or increasing fluid drainage) and provide pain relief. In the case of secondary glaucoma, the cause of the condition must be treated as well. This may include repair of trauma, surgical removal of any tumors, or antibiotics for infection. If only one eye is affected, steps will be taken to prevent glaucoma’s development in the other eye.

Medications

Most medications are topical drops or ointments that will lower the pressure of the eye and/or treat inflammation or infection. Topicals are often administered 3 times daily for a defined period of time. Some medications are oral.

Beta-blockers reduce fluid production. Carbonic anhydrase inhibitor diuretics reduce fluid production. Cholinesterase inhibitors help delay the onset of glaucoma in the unaffected eye. Corticosteroids can help control inflammation. Mitotic medications shrink the pupil to allow fluid release. Osmotic diuretics dehydrate the eye (used with caution in diabetics or cardiac patients). Prostaglandin analogs can improve fluid flow from the eye.

Surgery

Surgery may be required in cases of primary or secondary glaucoma. There are a variety of surgical approaches used for the varying degrees of severity and vision damage:

• Cyclophotocoagulation – A laser instrument destroys the secretory epithelium of the eye’s ciliary body (responsible for fluid production within the eye).
• Gonioimplantation – A shunt (small tube) is implanted to provide a fluid drainage outlet.
• Enucleation – Complete removal of the globe of the eye (eyeball). Used in severe cases or when other therapies aren’t effective.

Repeat surgeries may be required depending on the underlying cause and the eye’s response to surgery.

Glaucoma medications can help delay progression and provide comfort, but most pets lose vision in one or both eyes within two years without surgery.

If the condition is caught early, follow-up appointments will be scheduled to determine if treatment is helping or if the condition is worsening. The unaffected eye will continue to be examined for signs of glaucoma. When treating with drops, keep the tip of the dropper sterile. Never touch it to the surface of the eye or with hands. Surgery patients will need to wear an Elizabethan collar (e-collar or cone) to prevent rubbing the eye.

Breeds predisposed to developing glaucoma should have the eyes checked every 6 months so that cases can be detected and treated as early as possible. Always watch for any abnormalities with the eyes and report them to your vet as soon as possible.

In cases of enucleation surgery, loss of an eye is usually not difficult to adapt to and pets only suffer a mild loss of depth perception. You can speak with your veterinarian on how to make the house safe for transitioning to seeing with one eye. Watch off-leash pets outdoors as it will take a while to adapt fully.