My cat has an infected eye: what now?

In a cat an 'infected eye' is most often conjunctivitis: inflammation of the conjunctiva, the thin pink lining of the inner eyelids that also covers the front of the eye. It is the most common eye problem in cats, and many cats have at least one mild bout in their life.

Conjunctivitis is a sign, not a diagnosis. It can be one eye or both, and the eye looks red, wet or sticky. Finding the cause is what prevents complications and repeat episodes.

A red, weepy or sticky eye can also be something that looks the same but is more serious, such as a scratch or ulcer on the clear front of the eye (the cornea). Looks alone do not show which it is, so an eye that bothers the cat is worth a vet look.

Feline herpesvirus (FHV-1) is the most common cause of conjunctivitis in cats. It spreads by direct contact with a shedding cat and its tears, nose and mouth secretions, and it is a major part of 'cat flu'. Chlamydia felis is another common cause, especially in young cats, shelters, breeders and multi-cat homes. It often starts in one eye. Calicivirus gives milder, short-lived eye signs, usually together with mouth ulcers.

Bacteria such as Mycoplasma, Staphylococcus and Streptococcus also take part, often as a second infection on top of a virus or an injury.

Not every sore eye is an infection. Allergies (pollen, mould, dust mites, perfumes, household products), irritants (smoke, diffusers, cleaning products, dust, strong draughts from fans or air conditioning), a grass seed or another cat's claw in the eye, and scratches from a fight can all do it.

Eyelid and eyelash problems (lids that turn in or out, lashes growing the wrong way), a blocked tear duct, dry eye and lumps in or around the eye cause long-running weepy eyes. Eye signs can also come from illness elsewhere in the body, or from pressure or inflammation inside the eye. Frequent eye infections can point to an underlying condition such as cat flu. Parasites such as Thelazia (eye worms, spread by fruit flies) and tumours of the lid or conjunctiva are rarer causes that a vet can recognise.

A little dry crust in the inner corner is normal. More crust than usual, crust around the whole eye, or eyes that stay wet or stick shut are not.

Clear and watery discharge is the mildest kind. It fits an irritant or allergy, or the first day of a viral flare. Watch it, and have it checked if it lasts more than a day or two or the cat is bothered. White or grey mucus can mean conjunctivitis or a poor tear film. Thick yellow or green, pus-like discharge points to infection and calls for a vet appointment. Discharge that changes from clear and liquid to coloured and mucus-like, gets worse, or goes on for more than a few days needs a vet.

Brown or reddish-brown crust in the inner corner is often dried tears (staining), especially in flat-faced cats, but a herpes flare in an adult cat can also give brownish discharge. Bloody discharge is a reason to go the same day. The colour does not name the cause: pus-like discharge also comes from inflammation without a bacterial infection, so only the vet can tell what is behind it.

When the third eyelid slides across part of the eye, owners often describe a 'skin' or film over the eye. A pale or red membrane in the inner corner is rarely normal.

It can show with infections (especially viral), irritation, a painful eye or ulcer, or illness such as fever or dehydration. Only a vet can tell the causes apart. A third eyelid that stays visible for more than a short time, or comes with squinting, discharge or a sick cat, is a reason to book a vet appointment. Left alone it can lead to dry eye, ulcers or infection.

A cat that squints, holds the eye half or fully shut, blinks a lot, rubs its face or avoids light is in pain. A cat that keeps one eye tightly closed is usually in strong pain.

A corneal ulcer is a wound or crater on the clear front of the eye. In cats it is most often caused by a scratch from a fight or by herpesvirus, and it can come on top of conjunctivitis. An owner cannot see an ulcer: the eye may look only a little red, cloudy or blue-grey. Vets find it with a harmless dye (fluorescein) that glows under blue light. Herpes ulcers are often tiny dots or branching lines; one small series found them in 10 of 17 cats with herpes eye disease.

An ulcer left untreated is painful and can deepen, scar, or in the worst case cost the eye. A quiet eye does not rule it out, because some ulcers cause little pain. The vet decides the treatment, and the drops that suit conjunctivitis can be harmful on an ulcer. This is why eye drops should only be used once a vet has looked.

Scratches, bites, claws, plant material, sticks, a fall or chemicals can hurt an eye quickly. Cats that go outside are at higher risk, but indoor cats can get hurt on household items or in play.

A bulging or protruding eye, an eye that will not open, a cloudy eye with visible damage, a changed eye colour, blood in or around the eye or a visible wound are reasons to call an emergency vet at once. Any traumatic eye injury needs urgent assessment. Even a few hours can make a difference to sight.

Do not try to take something out of the eye yourself, and do not flush the eye with anything before the vet has seen it, unless the vet tells you to. Call the practice, keep the cat quiet in a carrier and go.

Kittens are among the cats most often affected. Their immune system is still developing, and cat flu passes quickly between kittens in shelters, breeders and multi-cat homes.

A kitten's eyes open at about 10 to 14 days. If pus builds up behind the closed lids and the lids swell or bulge, a vet needs to treat it. The vet cleans and opens the lids safely and checks the eye underneath. Do not pry stuck lids apart at home. Delay can lead to permanent lid adhesions and damaged eyes.

Kittens with an eye infection can also have a fever, tiredness, a blocked nose and breathing signs, and young kittens can become seriously ill from herpesvirus. A kitten with eye signs and poor eating or breathing trouble is a same-day case. Most kittens recover well with quick treatment.

Flat-faced cats such as Persians and Exotic Shorthairs have large eyes in shallow sockets and narrow or misaligned tear ducts, so tears spill onto the fur instead of draining. Brown or red tear marks down the face are common and cannot always be removed completely.

In a study of show Persians and Exotic Shorthairs (64 and 12 cats), a vet exam found eye discharge or staining in 83% and turned-in lids (entropion) in 32%; none of the comparison domestic cats had either. Few owners reported a problem, and the cats were mostly show cats, so it does not describe every cat of these breeds.

Staining is mostly a hygiene and cosmetic matter. Wiping the eye area once or twice a day with a clean, damp cotton pad or a vet-approved eye cleaner, wiping away from the eye, and keeping the face fur brushed and short around the eyes helps. Do not use wipes that are not made for cats' eyes, or hydrogen peroxide near the eyes. Redness, squinting, thick discharge or a cloudy eye in these breeds is still a vet matter and not just staining.

Persians and similar flat-faced cats are listed as higher risk for conjunctivitis, chronic ulcers and a black spot of dead cornea tissue (corneal sequestrum). Cats with past eye problems and these breeds benefit from regular eye checks.

After the first infection most cats keep feline herpesvirus hidden for life. About 95% of cats have met it and at least 80% carry it, often without signs.

Stress (a move, boarding, surgery, illness, a new pet) or steroid medicine can wake the virus, and the eye signs come back. Sick cats shed virus in eye, nose and mouth secretions for up to about three weeks. A flare in an adult cat often shows as slight squinting in one eye, more discharge and redness. Later episodes are usually milder, and one episode typically settles within about two to three weeks.

Repeated episodes call for a vet to look for the cause behind them. Long-term herpes can lead to dry eye, a scarred or black cornea, or thick white plaques on the eye surface that may need lifelong treatment. A positive herpes test does not always mean herpes is the cause of this eye problem, because healthy cats can test positive too.

Infectious causes (herpesvirus, Chlamydia felis, calicivirus, Mycoplasma) spread between cats through sneeze droplets, eye and nose secretions, shared bowls, litter trays, grooming and bedding. Eye problems from allergy, injury or irritation do not spread. Herpesvirus dies quickly with common disinfectants and survives only about 12 to 18 hours on surfaces.

For people the risk is small. The common cat eye viruses do not infect people, but Chlamydia felis can rarely cause mild conjunctivitis in a person, and some bacteria pass between cats and people. Wash your hands after touching the eyes and do not hold your face against a sick cat's face.

If the vet suspects a contagious cause, keep the cat apart from other cats during treatment, give each cat its own bowls, tray and bedding, and use separate towels and grooming tools.

Some mild cases from a temporary irritation do clear without medicine, and a healthy cat's simple conjunctivitis may settle by itself.

But looks do not show the cause. Infections often do not clear reliably without treatment, and a painful ulcer can look like simple conjunctivitis. So an eye that is sore, thick with discharge, or lasts more than a day or two needs a vet. Waiting to see whether a painful or squinting eye gets better can seriously affect sight.

Conjunctivitis is usually uncomfortable and often painful. Left too long it can lead to deeper disease, glaucoma, inflammation inside the eye (uveitis), a damaged cornea and permanent loss of sight or of the eye. A simple conjunctivitis rarely causes blindness on its own; delay or a missed serious disease is what raises the risk of lasting vision loss.

Glaucoma (raised pressure inside the eye) is painful and can quickly lead to blindness. Uveitis can follow infections such as FeLV, FIV or FIP and needs treatment of the eye and the cause. Sudden blindness shows as bumping into things, falling or seeming disoriented. In cats it is often linked to retinal detachment from high blood pressure with kidney disease, and it is an emergency.

The outlook is generally good with early treatment.

The vet looks closely at both eyes, the lids and the third eyelid, and asks about sneezing, vaccination status, other cats and recent events. A fluorescein dye test checks for an ulcer. Sometimes the vet numbs the eye or sedates the cat to examine it. A swab or PCR test may be taken for herpesvirus, Chlamydia felis or Mycoplasma, or a culture if an infection does not respond. Herpes is often diagnosed from the history and the look of the eye, because tests are not perfect. If the problem does not clear or keeps coming back the vet may measure tear production and eye pressure, or refer to an eye specialist.

Treatment follows the cause. Vets commonly use antibiotic eye drops or ointment when bacteria are likely (antibiotics do not act on viruses), lubricating drops, and pain relief chosen by the vet. For herpes the care is mostly supportive. Antiviral medicine is sometimes added in severe or recurring cases. One such medicine helped in studies but caused side effects in 17% of cats in field use, and no antiviral is licensed for cats according to one source, so the vet weighs it for each cat. Human antivirals can be toxic to cats. A vet may mention L-lysine for cats with herpes. A 2015 review concluded it is likely not effective, and evidence is mixed, so it is a question for the vet and not a cure.

Chlamydia is commonly treated with a course of tablets over several weeks, and in multi-cat homes treatment often continues for about two weeks after the signs have gone. An ulcer is treated with antibiotic and lubricating drops, sometimes drops to ease eye spasm, pain relief, and a cone collar until the vet says it can come off. Deep or stubborn ulcers may need surgery by an eye specialist. A foreign body is removed by the vet, sometimes under sedation. Dry eye is eased with artificial tears. Eyelid problems may need corrective surgery.

Typical time to improve: a bacterial case often starts to improve within two to three days and mostly clears in one to two weeks; a herpes flare often takes one to three weeks; Chlamydia or Mycoplasma several weeks. Go back to the vet if there is no change after about three days, or an ulcer is not clearly better after a week. The full course should be finished even when the eye looks normal, or the infection can come back.

While waiting for the vet visit, a very sore, sticky eye is commonly wiped gently from the inner corner outward with a clean cotton pad or gauze dipped in lukewarm water, using a fresh piece for each eye. Gauze does not shed fluff the way cotton can. This eases the eye and is not a treatment. Do not press on or rub the eyeball. A warm, damp cloth held on the closed eye for a minute or two may soften crusts.

Keep the cat from rubbing the eye. A soft collar or cone can help if the cat tolerates it, and a vet-prescribed cone should stay on until the vet says otherwise. Keep the home calm, dust-free and smoke-free, and avoid sprays and strong cleaners near the cat. Offer blended, tasty, slightly warmed food to a cat with flu signs that is not eating, and ask the vet about further care.

Cat flu vaccination is the main protection against the viruses that cause most infectious conjunctivitis. It makes disease milder and shorter but does not always prevent infection, and a vaccinated cat can still get eye signs. Vaccines exist for herpesvirus and calicivirus, and for Chlamydia felis. The Chlamydia vaccine reduces signs without preventing infection and is considered mainly for multi-cat homes.

Keep stress low for cats that carry herpes: a steady routine, enough to do and gradual changes. Clean bowls, bedding, litter trays and grooming tools regularly, especially in multi-cat homes. Avoid smoke, sprays and irritating cleaners. Check your cat's eyes now and then. Cats hide pain, so early eye problems are easy to miss. Groom the face of flat-faced cats.