Glaucoma in Dogs

What is Glaucoma in Dogs?

Glaucoma is an eye disease caused by increased pressure inside the eye. Also known as intraocular pressure (IOP), this condition is a result of an imbalance in the production of fluid and drainage.

The eye produces a fluid called aqueous humor from an area called the ciliary body. This fluid contains oxygen and nutrients that feed all ocular structures. Once these structures are fed, the remaining fluid is emptied via the iridocorneal angle — an area between the outer layer of the eye, the cornea and the iris, the pigmented/colored portion of the eye.

IOP should remain normal and consistent if drainage and production are equal. If they’re not, there is increased pressure behind the eye and glaucoma is present. The condition is caused by decreased drainage of the aqueous humor, not overproduction.

There are two types of glaucoma:

Open-angle glaucoma, a slow, chronic progression of blindness.

Closed-angle glaucoma, a sudden increase in IOP that leads to acute pain and blindness.

Increased IOP causes damage to:

• The optic nerve, which carries visual messages taken in from the eye to the brain

• The retina, which senses light in the eyes and sends signals to the brain to create images

• The optic disk, where the nerve enters the eye

This condition is often painful and can acutely or slowly cause blindness due to continued damage to the optic nerve. Blindness can be prevented, or at least delayed, with a prompt diagnosis.

Symptoms of Glaucoma in Dogs

Acute glaucoma is easier for dog owners to recognize due to sudden changes to the eye and signs of pain. Gradual onset of glaucoma is often missed by pet parents, as the clinical signs can be subtle. Clinical signs noted in dogs with acute severe glaucoma include:

• Dilated pupils that are nonresponsive to direct light

• Redness in the whites of the eye

• Swelling and/or bulging of the eye

• Rubbing and/or scratching at the eye

• Sleeping more, or acting quieter than usual

• Squinting or avoiding being touched near the affected eye

• Decreased appetite

• Increased watery discharge from the eye

• Sudden blindness — bumping into things, not wanting to move around the house as much and sudden anxiety

Clinical signs associated with mild to moderate chronic glaucoma include:

• Cloudy or hazy blueish appearance to the outer layer of the eye

• Slightly dilated pupils that are slow to respond to light

• Plump or slightly distended eye veins in the white of the eye

• Slight eye enlargement

Prolonged, elevated IOP causes the eyeball to look very large and even feel firm to the touch. It can cause the lens (the small, rounded structure behind the iris that acts to focus light) to be displaced from its original location. Elevated IOP can eventually lead to a rupture of the eye from the continued pressure.

Causes of Glaucoma in Dogs

Primary glaucoma is caused by increased IOP in an otherwise healthy eye. It is often due to genetic, inherited abnormalities of the eye’s drainage angle.

• Goniodysgenesis is an inherited risk factor for closed-angle glaucoma and puts affected dogs at a higher risk of glaucoma in the future. It can be diagnosed through genetic testing, and dogs with this gene should have regular eye exams to check IOPs.

• Primary open-angle glaucoma causes a more gradual increase in IOP, and vision loss is very slow. Genetic testing is available for this condition.

Secondary glaucoma is the most common type in dogs, and is caused by increased IOP due to injury or a medical condition of the eye.

• Lens luxation occurs when the lens which usually sits behind the iris, dislocates in front of the iris, and blocks the drainage angle or the pupil, thus trapping fluid behind it.

• Uveitis (inflammation of the interior components of the eye) causes inflammation, debris, and/or scar tissue that blocks the drainage angle, causing fluid accumulation.

• Cataracts affect the lens of the eye and can cause inflammation or debris that blocks the drainage angle, leading to fluid accumulation.

• Tumors can lead to physical obstruction and/or inflammation, causing fluid accumulation and a lack of drainage.

• Bleeding in or around the eye from trauma, retinal detachment, etc., can prevent fluid drainage from the iridocorneal angle.

How Veterinarians Diagnose Glaucoma in Dogs

Glaucoma is considered a medical emergency, so if you note any changes in your dog’s eyes that concerns you, bring your pet to a vet as soon as possible. Physical examination, history of onset of symptoms, and any other major medical issues should be considered — especially if trauma to the eye has occurred.

Intraocular pressure is measured and compared in both eyes using an instrument called a tonometer. Elevated pressures in one or both eyes confirms glaucoma. The next step may be referral to a board-certified veterinary ophthalmologist who can perform a gonioscopy to evaluate the drainage angles of the eyes.

Ocular ultrasound and/or electroretinography may also be considered by the specialist depending on presentation and severity of the symptoms.

Treatment of Glaucoma in Dogs

It is vital to decrease IOP as soon as possible to lessen the risk of blindness and damage to the optic nerve. Because of this urgency, treatment is started as soon as possible. Any underlying disease process causing glaucoma needs to be determined and treated to appropriately treat the condition.

Usually, multiple ophthalmic medications are prescribed to lower the IOP to normal range as quickly as possible. These medications help drain fluid from the eye and include:

• Eye drops — including carbonic anhydrase inhibitors (such as Orzolamide), prostaglandins (such as Latanoprost), and beta-adrenergic blocking agents (such as Timolol) — to help drain the fluid from behind the eye to lower IOP acutely.

• Analgesics, or pain medications, to treat the discomfort associated with this medical condition.

In severe cases where the optic nerve has minimal damage, cyclocryotherapy may be considered. This treatment uses very cold temperatures to kill the ciliary body cells that produce fluid within the eye.

Another possible procedure is an injection of specialized medication into the eye itself. This, too, destroys the cells that produce fluid. With early diagnosis, these procedures can slow further progression.

Often, in severe cases where the optic nerve has irreversible damage, surgical removal of the eye is performed. This eliminates the source of pain and the need for continued glaucoma therapy at home. Most dogs adjust quickly to their environment after a surgical eye removal.

Recovery and Management of Glaucoma in Dogs

Most glaucoma cases require lifelong treatment. Frequent visits to the vet for IOP monitoring and medication adjustments will be necessary, especially at the start of therapy.

Most pets with glaucoma are affected in both eyes. If glaucoma is found in only one eye, steps are usually taken to protect the unaffected eye. This is especially important with primary glaucoma (inherited), as more than 50 percent of dogs develop glaucoma in the unaffected eye within eight months of diagnosis in the affected eye.