Conjunctivitis in Cats: Causes, Symptoms, Treatments

Conjunctivitis is the most common of the feline eye disorders. Most cats will experience at least a mild episode at some point during their life. This means all cat parents need to be able to recognize conjunctivitis in cats. 

In this article, we’ll go over all things cat conjunctivitis, so you’ll be able to look out for the warning signs and know what to do if your cat is infected.

What Is Conjunctivitis?

The moist tissue that lines the eyelid and eye surface is called the conjunctiva. The part directly on the eye is called the bulbar conjunctiva, and the lining inside the eyelids is called the palpebral conjunctiva. When these mucous membranes become inflamed, it’s called conjunctivitis.

Most people are familiar with conjunctivitis in humans, but you may wonder how it compares to cat conjunctivitis. For example, what causes conjunctivitis in cats? And is conjunctivitis in cats contagious?

Conjunctivitis in cats is usually infectious, so yes, in those cases it is contagious and can be passed to other kitties. The risk to non-feline family members (both dogs and humans) is low. 

Now let’s go over what can cause cat conjunctivitis.

Causes of Conjunctivitis in Cats

The three most common infectious causes of conjunctivitis in cats are:

• Feline herpesvirus-1 (FHV-1)
• Chlamydia felis, which is a bacteria
• Feline calicivirus (FCV)

Because these causes are infectious, your cat’s risk increases when they’re around a lot of other cats. If your cat is in a confined area with unfamiliar cats, their likelihood of contracting something from one of those cats becomes greater. Higher risk situations include animal shelters, boarding facilities, catteries, veterinary clinics, or outdoor cat colonies.

Another important factor for infectious conjunctivitis, particularly herpesvirus, is that it can recur in times of stress. When a person with herpesvirus-1 gets stressed, they get cold sores. When a cat with FHV-1 gets stressed, they basically get a cold, with conjunctivitis being one of the main symptoms. A stressed cat may have a recurrence of herpesviral conjunctivitis. Stressors could include a new animal or child in the home, moving to a new home, outdoor cats harassing them through the window, recent veterinary visits, and more.

Other less common causes of conjunctivitis can include:

• Trauma
• Chemical burns
• Environmental irritants
• Foreign bodies in the eye or under the eyelids
• Eye worms (Thelazia spp.)

You can also see inflammation of the conjunctiva secondary to other diseases of the eye, such as an ulcer on the cornea, rolled-in eyelids (entropion), or glaucoma.

Symptoms of Cat Conjunctivitis

Cat conjunctivitis can occur in one or both eyes. It may be the only sign you see, or you may notice upper respiratory signs, as well.

Some of the most common symptoms of conjunctivitis in cats include:

• Excessive blinking, winking, or squinting (blepharospasm)
• Ocular discharge, which can be clear, yellow, green, tan, or brown
• Redness of the eye
• Swelling around the eye, which can appear as excessive pink tissue around the eye
• Eyes crusted shut
• Ulcers on the cornea (surface of the eye)
• Pawing at the eyes
• Upper respiratory signs: sneezing, nasal discharge, poor appetite, lethargy, ulcers in the mouth, coughing

Diagnosing Feline Conjunctivitis

A physical examination is necessary to diagnose feline conjunctivitis. A full exam of the eye can include testing the eye’s tear production (Schirmer tear test), testing the eye for ulcers (fluorescein stain), testing the pressures of the eye (intraocular pressures), and examining the eye with a light source. Usually, your veterinarian will treat your cat for a presumed infectious cause based on their findings without additional testing.

If your cat’s symptoms are not resolving or recur frequently, your veterinarian may recommend additional testing to seek a definitive cause. Examples of additional testing could include polymerase chain reaction (PCR) or virus isolation. These tests involve sending samples to a reference laboratory, which will report back if specific infectious diseases are detected. Your cat may need to be sedated for sample collection.

How to Treat Conjunctivitis in Cats 

Treatment of conjunctivitis in cats depends on the underlying cause and severity. Most herpesvirus cases resolve on their own without treatment. If the disease is severe or isn’t improving, or if you have an immunocompromised cat – such as one with feline immunodeficiency virus (FIV) –  your veterinarian may recommend treatment. Supportive care, such as ensuring that your cat maintains adequate hydration and nutrition, is always important.

Keep in mind that two of the most common causes of conjunctivitis – herpesvirus and calicivirus – are viral. This means antibiotics aren’t going to make the virus go away. However, both viruses can easily cause secondary bacterial infections, in which case antibiotics may be beneficial. Your veterinarian may prescribe an oral antibiotic, usually doxycycline, or topical antibiotics that are placed directly within the eye. Topical antibiotics usually come in the form of either cat eye drops or eye ointment. If your veterinarian suspects herpesvirus, they may prescribe an oral antiviral like famciclovir or a topical antiviral like idoxuridine. Currently, antivirals are not routinely used for suspect calicivirus cases.

You can help your cat by gently wiping away excessive eye discharge. If your cat’s eyes are crusted shut, you can use a warm cloth compress to try to gently tease them open; however, this must be done with caution! The conjunctiva is a delicate tissue. With severe inflammation, the conjunctiva on the inside of the eyelids (palpebral conjunctiva) can become adhered to the surface of the eye (bulbar conjunctiva). This is called symblepharon. These changes can be permanent or may require a visit to an ophthalmologist, and pulling on the eyelids may cause the tissue to tear.  To help avoid this complication, use a warm compress to keep your cat’s eyes open and seek prompt veterinary attention.

How to Prevent Conjunctivitis in Cats 

Not all cases of conjunctivitis are preventable, but there are steps you can take to reduce the risk and severity of disease.

One of the key things you can do is keep your cat up to date on vaccinations. The FVRCP vaccine, which is a core vaccination for cats, protects the cat against both herpesvirus and calicivirus. While the FVRCP vaccine doesn’t prevent all cases of herpesvirus or calicivirus, it’s thought to reduce the severity of disease. The vaccine may also decrease shedding of herpesvirus, reducing the likelihood of transmission between cats.

Importantly, it’s likely that your cat has already had or currently has herpesvirus and/or calicivirus, as both viruses are very common. In fact, according to the Cornell Feline Health Center, up to 97% of cats are exposed to feline herpesvirus in their lifetime, and up to 80% of exposed cats have a lifelong infection. Of those cats, up to 45% will occasionally shed the virus, usually following times of stress. So statistically speaking, the cat in your home very likely already has herpesvirus. 

When it comes to calicivirus, the Cornell Feline Health Center states that 10% of cats housed in small groups are affected, while up to 90% of cats in more crowded situations, like shelters, are infected. Even Chlamydia felis is common! Around 20% of cats with upper respiratory signs and 3% of healthy-looking cats carry C. felis. 

Theoretically, you could reduce your cat’s risk by keeping them indoors and away from densely populated areas, but the truth is that it’s very likely they’ve already been exposed to at least one of the main three infectious causes of conjunctivitis.

As previously mentioned, herpes can recur in times of stress. Reducing your cat’s stress by providing them with a regular routine and plenty of enrichment may help to prevent recurrence of herpes signs. When changes do occur in your home, try to slowly introduce your cat to those changes, if possible.

If you notice that your cat has red eyes or other eye problems, make sure to contact your veterinarian for further advice.