What Causes Cat and Dog Eye Infections? How to Know What's Causing Your Pet's Eye Infection

What Causes Cat and Dog Eye Infections?
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Eye infections in dogs and cats can be caused by viruses, allergies, or injury, to name a few. Learn what causes eye infections in pets.

Dogs and cats are more susceptible to different types of eye infections, and some breeds are more prone than others.

The most common causes of eye infections in dogs are allergies, blocked tear ducts, and corneal ulcers.

For cats, the most common causes are allergies and infectious organisms like calicivirus (FCV), herpes, and chlamydia.

Other causes are:

  • A foreign object or irritant in the eye like dirt or pollen
  • Developed or congenital (from-birth) defect of the tear ducts
  • Bacteria
  • Viruses
  • Fungus
  • Parasites

Dog breeds like Maltese, Pekingese, Pugs, and Shih Tzus are all genetically predisposed to be more likely to contract an eye infection. Cocker Spaniels and Poodles are prone to blocked tear ducts. Persian and hairless cats are more prone to eye infections than other cat breeds.

In general, indoor cats are less likely to get eye infections than dogs and outdoor cats, simply because they are in contact with fewer substances.

The Causes of Eye Infections

Conjunctivitis: Conjunctivitis is an inflammation of the conjunctiva, the membranes that line the eyelids. These are meant to be a protective barrier that keeps dust and other unwanted particles out of your pet’s eyes. Conjunctivitis can be caused by chlamydia, a bacterial infection, in which case your pet will probably also be suffering from an upper respiratory infection, resulting in sneezing, nasal discharge, and nasal infection. Conjunctivitis is very contagious between pets, so keep your pet away from others until you can get them to a vet. The bacteria that cause conjunctivits in animals can't be passed to humans, though.

Dry Eye: Dry eye, or Keratoconjunctivitis Sicca (KCS) is a disorder that causes the immune system to attack tear glands and prevent the productions of tears. When a pet has dry eye, a thick mucous layer will cover the eye. When the eye isn’t properly moistened by healthy tears, the eye dries out, and mucous develops to try to protect the eye where tears can’t. This is very uncomfortable for pets, and can impair vision.

Corneal Ulcers: Corneal ulcers are wounds on the cornea, or the outer layer of the eye, that can be caused by injury or a foreign body scratching the eye or becoming trapped by the eyelid. Small or shallow scratches on the cornea can often heal by themselves, but more serious injuries can develop into ulcers. Or, small scratches may fail to heal because of malfunctioning tear ducts, bacterial or fungal infection, or feline herpes in cats. 

Cherry Eye: Cats and dogs have what’s called a third eyelid, or another membrane under their outer eyelid. Also called the nictitating membrane, this eyelid can be seen in some pets at the corners of their eyes, and in other pets can only be seen when it’s closed, usually in response to pain. Cherry eye is a prolapse of the third eyelid tear gland, which means the gland bulges from under the eyelid and is visible as a red-colored growth. If left untreated, cherry eye can cause conjunctivitis.

Entropion is a turning-in of the eyelid margins, or edges, making blinking difficult and painful for your pet. This can be congenital, meaning it’s formed in your pet before birth, or caused by loose skin or scarring around the eye. Surgery may be needed to correct the eyelid and prevent damage to the cornea or infection.

Uveitis is an inflammation of the inner pigmented structures of the eye. It can be cause by feline leukemia, feline immunodeficiency virus (FIV), or parasites like roundworms and heartworms. Uveitis causes blood or pus to leak into the front area of the eye. Antibiotics can help get rid of uveitis, and you’ll want to treat the infection right away, because it could develop into intraocular cancer.

Glaucoma: Glaucoma occurs when ocular pressure, or the pressure inside the eye, increases above normal. Blocked fluid inside the eye will cause this rise in pressure, and the increased pressure compresses the optic nerve. Your pet will experience pain, and glaucoma will eventually lead to blindness. Treatments can ease the pain and delay the loss of vision. 

Viruses: Many viruses that can attack your pet’s body will affect their eyes as well. Canine and feline distemper virus, feline immunodeficiency virus (FIV), feline calicivirus (FCV), and feline herpes are some common viruses that can cause eye infections. These viruses can cause flare-ups of eye infections for the pet’s whole life. Eye infections will strike in times when the immune system is weakened, like if your cat is experiencing other health issues or is stressed.

Bacteria: Chlamydia is the most common bacterial infection that results in eye infection. It often triggers conjunctivitis.

Fungus: Fungal infections can also result in bloody noses, fever, and coughing. Common fungal infections that cause eye infections are aspergillosis, cryptococcosis, valley fever, and blastomycosis. Blastomycosis can cause glaucoma and retinal detachment.

Other problems that can affect your pet’s eyes

Cataracts: Though not strictly infections, cataracts affect your pet’s eyes, and may mimic the symptoms of an eye infection. Cataracts are more common in dogs than cats. They are opaque spots on the transparent lens of the eye. If the cataracts grow so large that they impair your pet’s vision, your vet may recommend surgery. There’s no other way to get rid of cataracts once they’re formed, but a small opacity can sometimes be left alone, and your pet will be able to continue with their normal way of life. Genetic predisposition, diabetes, and dietary deficiencies can cause cataracts.

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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