Top 3 Causes of Conjunctivitis in Dogs
Conjunctivitis, sometimes called pink eye, is one of the most common causes of red, inflamed eyes in dogs. It causes other signs such as excessive sticky, mucopurulent, or pus-like discharge that is yellow, green, or white in color. Conjunctivitis is painful and can cause your dog to squint, have watery eyes, or rub at the eye.
What causes conjunctivitis in dogs?
When it comes to causes of conjunctivitis, cats and dogs differ. With cats, viral and bacterial infections are the most common. For dogs, trauma and direct contamination are more likely to cause these signs.
Let’s discuss the causes of canine conjunctivitis in more detail...
Contamination of the Eye
Curious canines like to investigate with their noses. For this reason, their head is often down a hole, in a hedge, or somewhere else inappropriate! It’s not surprising that dogs end up with a lot of unwanted debris in their eyes.
Although the eye does have defense mechanisms such as blinking and producing tears, dogs with eye irritation can rub them on the floor or scratch at them, making things worse. The contaminated eye (say, small particles, soil, or pollen) may react by calling for help from the immune system. This will increase the blood supply to the eye and cause redness. This redness may be temporary and settle quickly. However, if your dog is rubbing at the red, inflamed eye, they can injure the already delicate area. As a result, the bacteria that normally live in low numbers on the surface of the eye may take advantage of the situation and multiply. This often creates the sticky yellow/white/green discharge.
For a simple case of contamination, cleaning the eyes at home using large make-up removing pads soaked with filtered, distilled, or cooled boiled water can help remove debris from the eye. If the redness persists or is accompanied by increasing amounts of discharge, veterinary help must be sought. Your vet will be able to rule out other causes for your dog’s eye inflammation and develop an appropriate treatment plan.
This type of conjunctivitis is usually treated with flushing of the eye and/or antibiotic eye drops.
Infection of the Eye
Eye infections are usually caused by the bacteria that live on the surface of skin or eye in low numbers. In certain cases, these bacteria can multiply. The most common reason for this is a condition called Dry Eye. Although strictly a disease of the tear gland, the result is a dry, sticky eye that can’t effectively maintain itself and flush away contaminants and debris. Usually the first sign of the disease is conjunctivitis. Dry Eye is most commonly diagnosed in middle-aged dogs, with bulldogs, cocker spaniels and certain terriers being affected most commonly. Once the diagnosis is made, it can be treated effectively with eye drops and tear replacements. However, it's important to note that these are lifelong treatments and if stopped, the conjunctivitis will return.
As mentioned above, contamination of the eye by particles can end up causing a true bacterial infection from the body’s own surface bacteria. Less commonly, an eye may become infected by bacteria from the surrounding environment or by a colony of infectious bacteria transmitted from other dogs. This causes the typical signs mentioned above and again is treated by flushing the eye and antibiotic eye drops.
Although allergies in people such as hay fever typically exhibit as red itchy eyes, this is a much less common sign of allergy in dogs. Canine grass pollen and other allergies generally cause itchy skin, or redness around the eyes (on the skin) rather than in the eyes. However, rubbing in this area may cause secondary conjunctivitis. Less commonly, allergies can directly cause conjunctivitis. This should be suspected when the conjunctivitis persists, seems seasonal, or fails to respond to the treatments mentioned above.
Additional Causes of Conjunctivitis in Dogs
Other causes of red eyes in dogs include blocked tear ducts (these can be caused by conjunctivitis) or contamination with a large particle (such as a grass seed) that becomes lodged within the conjunctival sac or underneath the third eyelid.
An eye ulcer is another common presentation of a red eye in dogs and is often caused by trauma to the surface of the eye.
Finally, a cherry eye causes a red bulge in the corner of the eye and often causes a secondary conjunctivitis. It’s not uncommon in puppies of certain breeds of dog (brachycephalic pups, like Pugs, Bulldogs, and Shih Tzus).
What should I do if my dog has conjunctivitis?
Though it’s probably not an emergency, conjunctivitis can look like, or exist alongside a number of other more serious conditions like glaucoma, uveitis, or eye ulcers. If you think your pet has conjunctivitis, it’s important to see a vet for an exam as soon as possible.
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