Cat Eye Infection: Signs, Causes, and When To See a Vet

A cat eye infection is what most owners call it when an eye turns red, weepy, or crusty. The usual finding is conjunctivitis, inflammation of the pink tissue that lines the lids and covers the white of the eye. Many cases respond well to treatment, but not every red or weeping eye is infectious. Some are injuries that can cost a cat an eye if missed.

Never Put Drops in the Eye Without Your Vet

Do not put anything in your cat's eye that a vet has not prescribed for this problem. That means no leftover drops from an earlier illness, no human eye drops, no eye washes, and above all nothing that contains a steroid.

Steroids carry the biggest risk. The Merck Veterinary Manual says corticosteroids are contraindicated when a corneal ulcer is present, and that in cats, topical steroids can reactivate feline herpesvirus and cause corneal ulcers. Many ulcers are too shallow to see without special tests, so a steroid can land on an ulcer that nobody knows is there. A worsening ulcer can cost a cat the eye.

Old prescriptions are a problem too. VCA Animal Hospitals notes that a medication that helped with an earlier bout of conjunctivitis "may not help or may be harmful" this time. The right drop starts with an exam.

Cat Eye Infection Red Flags: When To See a Vet Today

Some eye problems cannot wait, whatever the cause. Go to your vet or an emergency clinic the same day if you see any of these:

• An eye that is held shut, or a cat that squints, blinks rapidly, or paws at the eye
• A cloudy or hazy surface on the eye
• A visible scratch, dent, or spot on the surface of the eye
• Blood in or on the eye
• One pupil larger than the other
• A bulging eye
• Sudden loss of vision, such as bumping into furniture
• An eye that is clearly getting worse, even over a few hours

The concern is the cornea, the clear dome at the front of the eye. Cornell's Feline Health Center explains that a corneal ulcer can worsen until it perforates, which "can result in blindness and even the loss of the affected eye." Ulcers are also painful. VCA says a corneal ulcer is "very painful," and that cats squint, blink rapidly, or keep the lids tightly closed to protect the eye.

What a Healthy Eye Looks Like

A healthy eye is clear and bright; the area around the eyeball looks white, and both pupils are the same size, according to the ASPCA. Check in good light. Gently roll down an eyelid with your thumb; the lining should look pink, not red or white.

An infected eye changes that picture. The lining turns red and swollen, the eye waters or discharges, and the third eyelid, the membrane in the inner corner, may show or swell. The crusty gunk in the corner that owners call cat eye boogers is dried discharge, and the ASPCA lists it among the signs to call your vet about.

What Causes Conjunctivitis in Cats

Cornell's Feline Health Center calls feline conjunctivitis the most common of all feline eye disorders, and infection is behind most cases. The most frequent causes by far are feline herpesvirus, calicivirus, and two bacteria, Chlamydophila felis and Mycoplasma. Young cats are hit hardest because kittens pass these germs around as they play, and infections are most common in multi-cat settings such as catteries.

Not every red eye is an infection. Dust, chemical irritants, allergens, dirt or plant material trapped under the lid, eyelashes that rub the cornea, and dry eye can all inflame the conjunctiva. Corneal ulcers, corneal infections, and other eye injuries cause redness and discharge too.

Because herpesvirus and calicivirus also cause upper respiratory infection, a cat with a weepy eye often has sneezing and congestion as well.

One Eye or Both? What Cat Eye Discharge Tells You

Which eye is affected, and what comes out of it, gives clues but not a diagnosis. One red eye leans toward a local problem. Merck lists a foreign object, an inflamed tear sac, or dry eye as causes of conjunctivitis in only one eye. A scratch or a trapped bit of plant material fits here too, and cats with outdoor access have more chances to pick up either one.

Both eyes lean toward a virus or bacteria, or toward allergies and irritants. So does a problem that starts in one eye and then spreads to the other, which Merck says is commonly caused by infection with a virus or bacteria.

Discharge follows the same rule. Clear and watery discharge leans toward a virus or an irritant, while thick yellow or green discharge leans toward bacteria. Merck notes that a cat with a viral eye infection often picks up a secondary bacterial infection, so the color can change as the illness goes on. Treat color as a clue only, because the look of the eye is usually not enough for a vet to name the cause without an exam and tests.

Why Herpesvirus Flare-Ups Keep Coming Back

Feline herpesvirus (FHV-1) is behind many eye infections, and the Merck Veterinary Manual describes it as extremely widespread among cats. After the first illness clears, the virus usually stays in the body in an inactive state for the rest of the cat's life. It can reactivate and cause flares, especially during times of stress.

A flare-up is not a sign that treatment failed. Cornell compares it to cold sores, which appear from time to time in people who carry the virus. VCA adds that illness can set one off too. Keep routines steady and learn the signs of stress in your cat, since stress is the usual trigger.

You will often see L-lysine recommended for herpesvirus. Whether it is worth trying for your cat is a question for your vet, who knows the history and what else is going on.

Vaccines and Prevention

Vaccines against feline herpesvirus and calicivirus are available. The ASPCA calls vaccinations and thorough checkups the best way to prevent eye conditions, and Merck says limiting exposure to sick cats, crowding, and stress adds to that protection.

Cat Eye Infection Treatment: What Your Vet Will Do

Your vet will start with your cat's history and a close look at the eye, the lids, and the tissue around them. The appearance of the eye alone usually cannot name the cause, so tests fill in the gaps.

The most common is the fluorescein stain. A drop of orange dye goes on the eye's surface, sticks to damaged areas of the cornea, and turns green. That is how vets find ulcers too shallow to see otherwise.

If dry eye is possible, a Schirmer tear test measures how many tears the eye makes. Some cats also need a sample from the eye sent to a lab, which can include testing for herpesvirus.

Treatment depends on the cause:

• Bacterial infection: antibiotic drops or ointment, which Cornell's Dr. Thomas Kern says are usually prescribed three or four times a day for two to three weeks.
• Herpesvirus: a topical antiviral medication alongside antibiotics. It cannot cure the virus, but it helps clear the surface of the eye so it can heal.
• Corneal ulcer: pain relief, medication to prevent infection, and often a cone so the cat cannot rub the eye. VCA says the eye should be rechecked two to three days after treatment starts.
• Foreign material, irritants, or eyelid problems: your vet checks for these and deals with them directly.

VCA says most bacterial and viral infections resolve within 5 to 14 days. Finish the whole course even when the eye looks better, because stopping early may let the infection return and make it harder to clear next time.

What You Can Safely Do at Home

Your vet will show you how to give the drops, and the ASPCA notes that many feline eye disorders are treated with vet-prescribed drops or ointments. Home care supports veterinary care rather than replacing it. At home, the job is comfort and cleanliness while that treatment works.

• Wipe crusty discharge from the lids and fur with a clean, damp cotton ball, moving away from the inner corner. Use a fresh one for each eye.
• Wipe the lids and fur only. Never flush, rinse, or wipe the surface of the eye itself.
• Keep the cone on if your vet prescribed one, because a rubbing paw can turn a small scratch into a bigger ulcer.
• Wash your hands after handling your cat, especially between cats. Merck notes that these viruses spread through droplets and contaminated objects that a handler can carry to another cat.

What To Do Today

Call your vet today for any new eye discharge, redness, or swelling, and go the same day for anything on the red-flag list. Cornell notes that many cases of conjunctivitis clear up on their own, yet it still advises a vet visit for eye discomfort with discharge to rule out something more serious. An exam is the only way to know which kind of eye issue you have.

Before you go, note when it started, which eye it is, and what the discharge looks like. A phone photo in good light helps. If your cat has had flare-ups before, ask your vet for a plan for the next one, so it does not catch you guessing.