There is nothing as heartwarming as staring into the loving eyes of your dog. But how much thought do you give to your dog’s eye health? Conditions like cataracts can affect your dog’s vision, and signs like cloudy eyes warrant a trip to your veterinarian. But there is another type of eye disease that may be harder to spot – glaucoma. Learning what to look for will help you identify the condition as soon as possible and provide your dog with appropriate treatment and pain relief.
What Is Glaucoma?
Increased pressure inside the eyeball, known as intraocular pressure (IOP), causes glaucoma in dogs. It’s caused by insufficient drainage of the aqueous humor (the fluid inside the eyeball that provides oxygen and nutrients to the organ’s structures). The eye is constantly making new fluid, so if it doesn’t drain at the normal rate, the fluid builds up and the pressure increases.
Veterinary opthalmologist Dr. Veronica Feigel, DVM, DACVO, explains glaucoma to her clients using an analogy of a water balloon with water constantly flowing in and out of it, keeping the balloon itself at a fixed level of fluid. “Fluid production inside of the eye and fluid outflow need to be in balance for the pressure of the balloon, or eye, to be normal. Glaucoma is when fluid outflow is affected, leading to fluid buildup inside the eye. This causes the eye, or balloon, to become firm and often subsequently enlarged.”
What Are the Two Types of Glaucoma?
There are two types of glaucoma: primary and secondary, but both result in an increase in IOP. The type that’s diagnosed depends on where the fluid exits the eye, known as the drainage angle. This is the structure through which the fluid normally drains.
In primary glaucoma, although the eye is otherwise healthy, there is an inherited abnormality in the drainage angle that affects the ability of fluid to exit the eye. This abnormality is hereditary in certain breeds of dogs, such as Akitas, Siberian Huskies, and Cocker Spaniels. Primary glaucoma commonly affects both eyes, with one eye being affected first, followed by the second eye later.
On the other hand, secondary glaucoma occurs when the drainage angle is anatomically normal, but there is some other eye issue affecting the fluid outflow. Some of those conditions include:
- Uveitis (inflammation inside the eye)
- Cancer in the eye
- Blood in the eye (hyphema). Blood clots can block fluid drainage.
- Pigmentary diseases and dispersion in the eye. Pigmentary dispersion happens when pigment granules (the cells that give the iris its color) disperse from the iris and travel through the eye, potentially blocking the drainage angle and leading to glaucoma.
- Complications post-intraocular surgery
- Displacement of the lens from its normal position (also known as lens luxation or subluxation)
What Does Glaucoma Do to a Dog’s Eye?
The eyeball is a delicate organ, and the high-pressure fluid buildup from glaucoma has many consequences. “The front part of the eye, the cornea, becomes very cloudy in the face of the high pressure, corneal edema,” says Dr. Feigel. “But most importantly, the tissue at the back of the eye, the retina, and optic nerve, are very sensitive to the high pressure. The high-pressure damages the retinal and optic nerve cells, eventually leading to cell death and permanent vision loss, unless the intraocular pressure can be reduced and kept well within normal ranges.”
What Are the Signs of Glaucoma in Dogs?
If glaucoma has such serious consequences, what should you look for to ensure your dog’s eye health? Dr. Feigel notes the most common signs include redness around the eye, cloudiness of the cornea, discharge from the eye, and pupil dilation. The eye may also look enlarged, bulging, or swollen due to the fluid buildup.
And your dog may become blind, sometimes quite suddenly. Finally, glaucoma hurts. You might see your dog hold their eye closed or rub at it. “Dogs that are experiencing a high intraocular pressure are also often lethargic and not themselves due to the severe pain glaucoma can cause,” Dr. Feigel adds.
How Is Glaucoma in Dogs Diagnosed?
As glaucoma in dogs can occur suddenly, with blindness following right behind, don’t hesitate to take your dog to the veterinarian immediately if something seems wrong. Your veterinarian will conduct a complete ophthalmic exam.
Dr. Feigel explains that further testing may help with a definitive diagnosis. “In order to definitely differentiate between primary and secondary glaucoma, there is also a test called a gonioscopy. This procedure involves placing a specialized lens onto the surface of the eye, allowing the ophthalmologist to visualize the drainage angle and assess whether it appears normal or abnormal. Specialized ultrasound can also be helpful in this process.”
What Is the Treatment and Outcome for Glaucoma in Dogs?
Whether it’s primary or secondary glaucoma, the initial treatment usually involves giving multiple eye drops to your dog to reduce the IOP. Fortunately, Dr. Feigel says these can often be successful. However, the time the eye drops work to keep the IOP under control varies by individual dog. With secondary glaucoma, treatment will also be aimed at addressing the principal cause of the drainage problem.
With primary glaucoma, Dr. Feigel explains there are other potential treatments. “There are also some surgical options for primary glaucoma that involve sending laser energy into the eye with the aim of destroying the cells that produce fluid inside of the eye – the ciliary body. There are different laser types, some applied to the external shell of the eye and some that are placed into the eye allowing for direct visualization of the fluid-producing cells. There are also small devices that can be placed under the shell of the eye to redirect fluid outflow, called gonioimplants. More recently, there are also some medication implants that can be placed to help reduce the intraocular pressure.”
As promising as these treatments sound, surgery comes with risks. Dr. Feigel warns the long-term outcome for vision in dogs with glaucoma is poor, whether or not surgery is performed. In many cases, when the eye becomes permanently blind and painful despite treatment, the eye must be removed (known as enucleation) to relieve the dog’s ongoing pain. Research into new glaucoma treatments, such as gene and stem cell therapies, could hold promise for better outcomes in the future.