Just as with humans, canines can sometimes suffer from a condition of the eyes called glaucoma. This is an increase of pressure that has built up inside of the eye. This type of pressure is called intra-ocular pressure, or IOP for short.
What is Glaucoma in Dogs?
Humans as well as dogs have a normal IOP of 10-20 mmHg. With glaucoma, 30 mmHg and sometimes even higher than 50 mmHg in pets is common, although human numbers are quite a bit less. When humans suffer from glaucoma, it’s usually at pressures ranging from 20-28 mmHg.
A healthy eye produces a clear fluid that is designed to nourish the tissues of the eye and help maintain its shape. This clear fluid is not the same thing as tears, which provide moisture and circulate around the surface of the eye to flush out debris.
The clear fluid is called aqueous humor, and is located ‘inside’ the eye, entirely separate from tears and their functions. In a healthy eye, aqueous humor fluid drains as if through a sieve, back into the bloodstream.
There is a balance required between the production of this fluid and its drainage in order to normalize eye pressure and sustain it within acceptable limits. When this balance is upset due to a blockage, pressure begins to build, eventually causing damage to the internal structure of the eye.
If the pressure isn’t relieved, the eye may stretch, enlarge, cause severe pain, and even result in loss of vision for your pet. This vision loss may be partial or total, and could wind up as permanent blindness.
Types of Glaucoma in Dogs
There are really only two types of glaucoma, primary and secondary. Primary glaucoma usually occurs because of physical or physiological traits that a dog has been predisposed to based on genetics. This means that the disease is inherited. The closer another dog is in the family tree that has suffered from glaucoma, the more likely it is that your dog will also suffer from glaucoma at some point.
Physical traits such as narrow angles or small pores that allow fluid to drain can also cause a blockage within the eye.
Glaucoma is not an exact science, and causes can vary from breed to breed. As a dog matures, clinical signs of glaucoma may occur in one eye or the other, though rarely at the same time or with equal pressure. Sometimes one eye can be affected months or years before the second eye is affected.
In secondary glaucoma, the disease is related to or triggered by something else, such as a wound that pierces the eye. Bleeding, swelling, and inflammation can occur, scar tissue may form, and drainage of fluid is hindered, if not blocked entirely.
Sometimes the tiny attachments that hold the eye in place are broken or weak, causing the lens to move out of its normal position and rest against the iris abnormally, hindering the eye’s ability to drain properly. This is called luxation/subluxation, or ‘lens instability,’ although even without a luxation or subluxation, the lens and iris can still attach together and cause fluid to be blocked. Sometimes scar tissue can build between the iris and lens as well, resulting in blockage.
Tumors, infections, advanced cataracts, cancer of the eye, inflammation, chronic retinal detachment are a few of the myriad of conditions that can trigger secondary glaucoma in dogs. However, the end result is the same – an inability of the eye to properly drain fluid and keep the pressure balanced, which is required for healthy vision.
Treatment will be different depending on the type of glaucoma, and will entail treatment of the root cause if it is secondary glaucoma, so it’s important to get an accurate diagnosis from your vet from the start.
Symptoms of Glaucoma in Dogs
Pain in dogs with glaucoma is more severe than pain in humans with glaucoma. However, animals don’t show pain the way humans do, and sometimes it can be hard for us to detect when our pet may be hurting. They won’t typically squint or rub their eye like you might do, although sometimes squinting or a slight fluttering of the lid is visible. If they do rub their eye, it may be against your leg or the furniture, but this is also a sign that’s easily missed.
Your pet may press their head against something in an attempt to relieve a headache, and may experience disinterest in normal activities as well as loss of appetite.
They can’t come out and tell you their head hurts or their eye hurts, so recognizing that something is wrong can be tricky. Also, when pets lose vision in one eye for any reason, they compensate so well that you may never even realize they are half-blind.
Optic nerve tissue is similar to brain tissue in that when it is damaged, healing is hard, if not impossible. Pressure damages to the optic nerve, along with stifled blood flow to the retina causes vision loss, and the longer the pressure remains without relief, the more damage and the greater the risk of permanent blindness. Permanent blindness in the first eye is common simply because it can be so easy to miss.
Rarely can you know your pet has increased pressure in their eye just by looking at them. Sometimes signs like red or bloodshot eyes may be visible, or the cornea could look ‘cloudy’.
Sometimes the pupil will look larger, or one eye may seem to protrude slightly. More often than not, everything looks normal, and even a vet can have a difficult time discerning something is wrong just by outward appearance.
The only reliable way to know early on if there is increased pressure in the eye of your animal is to have the IOP’s (intra-ocular pressures) measured by your vet. This can be tough if your dog is in pain or anxious. By the time the eye stretches and enlarges enough for you to visibly detect signs of glaucoma, it’s too late, and permanent blindness results.
Risk Factors for Glaucoma in Dogs