Conjunctivitis in Cats: Signs, Causes, and Treatment

What owners notice

Signs can affect one or both eyes. Infections often start in one eye and later spread to the other. Look for these changes.

• Red or pink tissue around the eye and inside the lids
• Watery tears, or discharge that becomes thick, cloudy, yellow or green
• Crusts on the lids or in the inner corner of the eye
• Squinting, frequent blinking or keeping the eye half closed
• Swollen pink tissue that can puff up around the eye like jelly
• A raised or reddened third eyelid, the thin membrane in the inner corner of the eye
• Pawing or rubbing at the eye, or avoiding bright light

Cats with a viral or Chlamydia infection may also sneeze, have a runny nose, seem tired or eat less. This is often part of cat flu, an upper respiratory infection.

Common causes

Infections cause many cases, especially in young cats and cats that live in groups.

Feline herpesvirus is found in cats worldwide and is especially common in shelters and large groups. After the first infection, nearly all cats keep the virus for life in a resting state. Stress, steroid medicines, nursing a litter or a big change such as moving home can wake it up again, so eye flare-ups can come back from time to time. In some cats the virus also causes sores on the cornea, the clear front window of the eye.

Chlamydia felis is a bacterium that mainly affects cats under one year old, especially where many cats live together. It often starts in one eye before spreading to both, usually with strong swelling of the pink tissue. It needs close contact between cats to pass on, mostly through eye discharge.

Mycoplasma bacteria can also cause conjunctivitis. Calicivirus, another common cat virus, mainly causes mouth ulcers, sneezing and a runny nose. It affects the eyes less often.

Some causes have nothing to do with germs. Dust, smoke, sand, plant material and chemicals can irritate the eye, and some cats react to allergens. Eyelids that roll inward rub hair against the eye, a problem seen more often in Persians and other flat-faced breeds. Dry eye, scratches and ulcers on the cornea can inflame the conjunctiva too. Glaucoma and inflammation inside the eye can look similar at first, and they need very different treatment.

Eyeworms are another cause. A small worm called Thelazia callipaeda has become established in continental Europe. It is carried by tiny flies that feed on tears and can infect dogs, cats, foxes and, rarely, people. Infected eyes are watery, itchy and inflamed. A vet can usually see the worms and remove them.

When it is an emergency

Mild redness with clear tears in a cat that is eating and playing normally is usually fine to have checked at a regular appointment within a day or two. Call sooner if it gets worse. It is best to contact a vet the same day if you notice any of the following.

• The eye is held shut or the cat squints hard
• The surface of the eye looks cloudy or bluish, or has a visible spot or dent
• The eye bulges, looks sunken or looks a different size from the other
• There is an injury, a scratch from another animal or something stuck in the eye
• A chemical, cleaning product or other substance got into the eye
• The cat is in obvious pain, hides or stops eating
• A kitten has eye discharge along with sneezing, low energy or poor appetite

Ulcers on the cornea and problems inside the eye can lead to scarring or loss of vision without treatment, so a painful eye is worth a same-day call. Newborn kittens can also develop conjunctivitis with large amounts of thick discharge. Any eye problem in a very young kitten is best checked by a vet without delay.

How vets find the cause

The look of the eye alone is usually not enough to tell the cause. Your vet will ask about the cat's history, such as where it came from, other cats at home, vaccinations and past eye problems. They will then examine both eyes closely, including behind the third eyelid, where small objects can hide.

Common tests include a dye that makes ulcers on the cornea show up bright green, a small paper strip that measures tear production and a quick check of the pressure inside the eye. Swabs from the eye, and sometimes the throat, can be sent for PCR testing to look for herpesvirus, Chlamydia or Mycoplasma. Because many healthy cats carry herpesvirus, the vet reads these results together with the exam.

How it is treated

Bacterial infections are usually treated with antibiotic eye drops or ointment. Chlamydia usually needs antibiotics by mouth for several weeks, often continued after the eyes look normal. Your vet may treat every cat in the household at the same time so the infection does not pass back and forth. Herpesvirus flare-ups may be treated with antiviral eye drops or antiviral medicine by mouth, especially when the cornea is affected. Allergies may be managed with anti-inflammatory medicine once infection and ulcers have been ruled out. Objects in the eye are removed, and eyelids that roll inward may need surgery.

Many cats start to look better within a few days of starting treatment. Chlamydia and herpesvirus can take longer to settle, and herpesvirus can return later, especially after stress. Eye medicine often needs to be given several times a day at first. It helps to give every dose, finish the course and keep the recheck, even when the eye looks better.

At home, gently wipe away discharge with a soft pad dampened with clean water or a saline rinse your vet recommends, and use a fresh pad for each eye. Keep the cat warm, calm and indoors while it recovers. Cats with a blocked nose may lose interest in food, so tell your vet if your cat eats less than usual. It is best to avoid leftover drops, another pet's medicine or human eye products unless your vet advises them. Some eye medicines, including those with steroids, can make an ulcer or a herpesvirus infection worse.

Spread to other pets and people

Infectious conjunctivitis spreads between cats through close contact, eye and nose discharge, shared bowls and bedding, and on hands and clothing. Calicivirus in particular can survive on dry surfaces for weeks. It is a good idea to keep a cat with red, weepy eyes apart from other cats until your vet has checked it. Wash your hands after handling the cat or its eye medicine, and give it its own bowls, bedding and litter tray for now.

Feline herpesvirus only infects cats and their wild relatives, so it does not spread to dogs or people. Chlamydia felis has passed from cats to people on rare occasions, usually as an eye infection. Hand washing after handling the cat is the main protection, and anyone with a weakened immune system can ask their own doctor for advice. Eyeworms can infect dogs and, rarely, people, and they spread through the flies that feed on tears.

Prevention

Vaccines against feline herpesvirus and calicivirus are core vaccines recommended for every cat. They reduce how sick cats get and how much virus they spread, though vaccinated cats can still catch and carry these viruses. A Chlamydia vaccine also exists, mainly for groups of cats where the infection is a known problem.

Keep a new cat separate from resident cats at first, and have it checked by a vet before they meet. Clean bowls, bedding and litter trays often. Keep stress low, since stress can bring herpesvirus back. Avoid smoke, dusty litter and sprays near the cat's face.

Newly adopted cats

The stress of moving to a new home can wake up herpesvirus that a cat already carries, so red or weepy eyes may appear soon after arrival, even in a cat that was healthy and fully vetted at adoption. Mild watery eyes and a few sneezes after a move are common, and it is still worth calling your vet.

At Paw Squadron, the first stops after every rescue are the vet and a bath, with a checkup, deworming and treatment against fleas and other parasites. Every animal gets a checkup, treatment, vaccinations and a microchip before adoption. If your adopted cat develops red or weepy eyes after coming home, share its history with your vet. Answers to common adoption questions are in our FAQ, and more cat health guides are in PawPedia.