Cat eye discharge: what the colour and texture actually mean

Quick answer

Both eyes open the same width, both equally bright, no film over the surface. This is the baseline you are comparing against.

The colour of the discharge tells you what kind of inflammation is happening. It does not tell you how urgent the eye is.

Urgency is decided by the eye itself: whether the cat is holding it shut, whether the surface has lost its shine, whether the pupil has changed, and whether the cat will let you near it. A watery clear discharge from a tightly closed, painful eye is a far bigger problem than thick green discharge from a wide open, comfortable one.

• Clear and watery means irritation, pain, or a drainage problem. It is the discharge most often attached to a corneal ulcer.
• Grey or white and stringy means mucin, usually chronic irritation or a dry, poorly lubricated surface.
• Yellow or green means pus, so white blood cells, so bacteria are now involved even if they did not start it.
• Rust brown staining on the fur is not blood and not infection. It is tear pigment that has oxidised, and it means the eye has been overflowing for a while.
• Squinting, cloudiness, a changed pupil, or blood are same-day problems regardless of colour.

:::danger
Never put drops containing a steroid into a cat's eye unless a vet has stained that eye and confirmed there is no ulcer.

Steroids suppress the corneal repair response and encourage the enzymes that break collagen down. On an ulcerated cornea they can convert a superficial defect into a melting ulcer and then a perforation within a day or two. This is the single most damaging thing owners do with leftover drops, because the label rarely says "steroid" in plain language. Words such as prednisolone, dexamethasone or hydrocortisone in the ingredients mean steroid.
:::

Decide in 60 seconds

Why the colour tells you what, not how bad

Tears are not just salty water. The film covering the eye has an oily outer layer from glands in the eyelid margin that stops evaporation, a watery middle layer from the lacrimal gland, and a sticky mucin layer produced by goblet cells in the conjunctiva that binds the whole film to the cornea.

Discharge is that film, altered. Which part has changed tells you what kind of process is running.

Serous, meaning clear and watery. The aqueous layer is being produced in excess, or it is being produced normally but cannot drain. Excess production is a reflex response to pain or irritation. Failed drainage happens when the tear duct that runs from the inner corner of the eye down into the nose is blocked or, in flat-faced breeds, distorted by the shape of the skull.

Mucoid, meaning grey or white and stringy. Goblet cells are working hard, which happens with chronic surface irritation and with a tear film that is too thin to protect the cornea. Thick, tacky, ropey discharge with a dull looking cornea raises the question of dry eye, which is less common in cats than dogs but does occur, particularly where herpesvirus has damaged tear-producing tissue.

Purulent, meaning yellow, cream or green. The colour comes from neutrophils and their breakdown products. This means bacteria are involved. It does not mean bacteria started it. In cats, most bacterial conjunctivitis is a passenger on top of a viral or structural problem, which is why antibiotic drops alone so often produce a partial improvement followed by relapse.

Rust or reddish brown on the fur below the eye. Porphyrins are pigments excreted in tears. They darken on exposure to air and light, so a pale-faced cat with any chronic overflow develops the classic stain. It is a chronic overflow marker, not blood, not infection.

Frank blood. Blood in the discharge means trauma, a deep ulcer, a mass, or a clotting problem, and blood pooling inside the front of the eye is an emergency in every case.

What healthy looks like

Look at the cat in daylight, from the front and then from each side at eye level. Compare the two eyes against each other, because your best reference for one eye is always the other one.

Both eyes should be open to the same width. The surface should act like a mirror: you should see a crisp reflection of the window in it. Any softening or scattering of that reflection means the corneal surface is disturbed.

The white of the eye should be white with fine, thin pink vessels. The third eyelid, the pale membrane at the inner corner, should be barely visible.

Pupils should be the same size and should both narrow when light hits them. A cat's pupil is a vertical slit in bright light and round in dim light, and it changes fast, so judge them at the same moment in the same light.

A small amount of dark crust in the inner corner overnight is normal in many cats, particularly darker coloured ones, and it wipes away easily.

A dated log and a weight are worth more at the appointment than any description from memory. Note which eye started first, what the discharge looked like each day, and anything you put in it.

Changes that mean act today

The eye is being held shut.

Blepharospasm is pain. Cats do not squint for fun. The two commonest causes are a corneal ulcer and a foreign body lodged under the third eyelid, and both are treatable if seen quickly and sight-threatening if not.

The cornea has lost its shine, or looks blue, grey or hazy.

Corneal oedema means fluid has entered the corneal tissue, which happens when the surface or the inner lining is damaged, or when pressure inside the eye is raised.

The pupil has changed.

A constricted pupil on the painful side with a duller iris is the classic picture of uveitis. A widely dilated pupil that does not respond to light in a cloudy, possibly enlarged eye suggests glaucoma, which in cats is usually secondary to uveitis and destroys sight quickly.

The third eyelid is up across the eye.

It rises with pain, with dehydration, with a mass behind the eye, and as part of a specific syndrome affecting both eyes in some cats. In every case it needs looking at.

Swelling around or behind the eye.

An eye that is being pushed forward, or one where the cat resents the mouth being opened, may have an abscess or mass behind the globe.

What is actually causing it

Feline herpesvirus-1. The dominant cause of eye discharge in cats worldwide. First exposure is usually in kittenhood, often with sneezing and a snotty nose, and the virus then remains latent in a nerve for life. It reactivates under stress: a new cat, a house move, boarding, surgery, another illness. Adult flares are often one-sided. It can produce branching corneal ulcers, which are close to diagnostic when seen with fluorescein, and long term it can scar the surface or fuse conjunctiva to cornea.

Chlamydia felis. A bacterium, and one of the few genuine primary bacterial causes. It produces very marked swelling of the conjunctiva, so the pink tissue around the eye looks puffy and raised. It typically starts in one eye and moves to the other over days, and it favours young cats and multi-cat households. It is treated with systemic antibiotic, usually doxycycline, for a full course, not with drops alone. Vaccines exist in some markets.

Mycoplasma species. Similar picture, similar treatment logic.

Feline calicivirus. Usually more mouth ulceration and lameness than eye trouble, but it belongs on the list in a young cat with a snotty face.

Corneal ulcer. Trauma, a cat fight scratch, herpesvirus, or a foreign body. Watery discharge, squinting, third eyelid up. Diagnosed with fluorescein dye in seconds.

Foreign body. A grass awn or plant fragment lodged under the third eyelid. Sudden, unilateral, intensely painful. Needs topical anaesthetic and a proper look behind the third eyelid, which is not something to attempt at home.

Uveitis. Inflammation inside the eye. The important point is that in cats it is very often a symptom of a body-wide disease: feline immunodeficiency virus, feline leukaemia virus, feline infectious peritonitis, toxoplasmosis, bartonella, lymphoma, or high blood pressure. A cat diagnosed with uveitis should have a systemic workup, not just drops.

Eyelid problems. Entropion, where the lid rolls inward and the lashes rub the cornea, is more common in flat-faced breeds and in older cats that have lost facial fat. Eyelid agenesis, a congenital gap in the upper outer eyelid, is a specifically feline defect that produces lifelong irritation and needs surgery.

Corneal sequestrum. A brown or black plaque of dead corneal tissue, seen particularly in Persians, Himalayans, Burmese and Siamese, often following chronic irritation or herpesvirus. It looks alarming and it is a surgical problem.

Eosinophilic keratitis. A pink, raised, slightly gritty plaque growing across the cornea, largely a feline condition, treated quite differently from an infection.

Nasolacrimal drainage failure. Common in Persians, Exotics and other flat-faced cats, where the duct is kinked by skull shape. The result is a permanently damp, stained face on a cat whose eyes are otherwise comfortable. Management, not cure.

Tumours. In older cats, a mass on the eyelid margin or third eyelid. In white or pale-faced cats in high sunshine regions, squamous cell carcinoma affecting unpigmented eyelid skin is a genuine risk and is why shade and sun avoidance matters for those cats.

How this changes by age, breed and household

Kittens. Discharge appearing before the eyes have opened, or bulging closed lids in a young kitten, is an emergency: infection is trapped behind the sealed lids and can destroy the eye. The lids must be opened by a vet. Whole-litter outbreaks are usually herpesvirus or chlamydia, and damage sustained now, including conjunctiva fused to cornea, is permanent.

Adult cats. Recurrent unilateral discharge with no other cat affected is most often a herpes flare. Look for the trigger in the two weeks before it started.

Senior cats. New uveitis, a lump on the lid, or sudden change deserves blood pressure measurement and bloodwork. Hypertension in older cats is common, treatable, and frequently first picked up through the eye.

Flat-faced breeds. Persian, Exotic Shorthair and Himalayan cats have shallow orbits, prominent eyes, distorted tear ducts and often some degree of entropion. Their baseline is a slightly damp inner corner. That makes it harder to spot when something has genuinely changed, so photograph the normal face while the cat is well.

Multi-cat households and recent adoptions. A new arrival with eye discharge, especially from a shelter or a group setting, should be isolated until seen. Chlamydia and herpes both spread by direct contact and by shared bedding and hands.

Check the whole cat, not just the eye. Appetite, drinking, sneezing and energy separate a local eye problem from an infection or a systemic disease that happens to show in the eye first.

The home routine that keeps an eye safe until the appointment

Cleaning is supportive care. It is not treatment, and it must never delay a vet visit for a painful eye.

Use cooled boiled water or sterile saline on cotton wool or a soft gauze pad. Wipe from the inner corner outward, once, then discard the pad. Use a fresh pad for the second eye, always, because using one cloth on both eyes is how a one-eyed problem becomes a two-eyed one.

For crusted, stuck-together lids, hold a warm damp pad against the lids for half a minute to soften the crust rather than pulling at it. Pulling tears the delicate lid margin.

Do not use cotton buds near the eye, do not use tissue that sheds fibres, and do not use any wipe containing fragrance, alcohol or a preservative sold for general pet cleaning.

Take photographs in daylight before you clean, since the appearance you are describing will be gone by the time you get to the clinic.

What never to do

Never apply a steroid-containing drop without a fluorescein test.

Covered above, and worth repeating because it is the mistake that costs eyes.

Never use human decongestant or redness-relief drops.

They work by constricting blood vessels, which removes the redness that was your best warning sign and does nothing to the underlying problem.

Never flush an eye with anything other than sterile saline or cooled boiled water.

No tea, no chamomile, no diluted disinfectant, no boric acid solutions, no salt water mixed at home to an unknown concentration.

Never assume improvement means resolution in a herpes flare.

The eye often looks better within days and the virus is still there. Stopping antiviral treatment early is a common reason for a rapid relapse.

Do not rely on lysine supplements as the answer.

Lysine is widely sold for feline herpesvirus, but controlled studies have not shown a consistent benefit, and in group housing settings some work has suggested it may make things worse. It is not a substitute for having the eye examined and treated.

Do not delay because the cat is still eating.

Cats with severe eye pain very often eat normally. Appetite is a poor guide to ocular urgency.

What the vet will ask for and what they will do

Expect these questions, and have the answers ready:

• Which eye started, and how many days ago
• Whether the discharge changed character over time, for example clear on day one and yellow by day three
• Whether the cat is squinting, rubbing, or light-shy
• Sneezing, nasal discharge, mouth ulcers, appetite, energy
• Vaccination history and whether the cat goes outdoors
• Other cats in the house, and whether any of them are affected
• Recent stress: new pet, new baby, house move, boarding, building work
• Everything already put in the eye, including leftover prescriptions and over-the-counter products

The examination follows a fairly fixed order. A general look for asymmetry and for the reflection off each cornea. Fluorescein stain, which is applied as a drop and shows up green where the corneal surface is missing, and which must be done before any steroid decision. A Schirmer tear test if the discharge is thick and the surface looks dull. Measurement of pressure inside the eye if there is any suspicion of glaucoma or uveitis. An examination behind the third eyelid, usually after a drop of topical anaesthetic, in any sudden unilateral painful eye.

A conjunctival swab for PCR can distinguish herpesvirus, chlamydia and mycoplasma, and it is worth asking for when the problem is recurrent, when a whole household is affected, or when a first course of treatment failed.

If uveitis is confirmed, expect blood pressure measurement, retroviral testing for FeLV and FIV, and general bloodwork, because in cats the eye is often reporting on something elsewhere.

Referral to a veterinary ophthalmologist is appropriate for a non-healing ulcer, a sequestrum, eyelid agenesis, glaucoma, or anything where sight is at stake. Availability varies enormously by country and region, so ask early rather than after two failed treatment courses.

When to get help

Go the same day for any of these:

• The cat is holding an eye shut or half shut
• The cornea is cloudy, blue, or has lost its mirror-like reflection
• The pupils are different sizes, or the iris looks a different colour or texture
• Blood in or around the eye
• Thick discharge gluing the eyelids together
• Any eye problem in a kitten, including discharge before the eyes have opened
• Discharge alongside not eating, lethargy, or laboured breathing

Daylight at a window is the best light for the daily check. Judge both eyes at the same moment, in the same light, and look for the reflection on each cornea.

Go immediately, out of hours, if the eye looks enlarged or bulging, if the cat is in obvious pain and cannot settle, or if there has been a known injury such as a cat fight scratch to the face.

Book a routine appointment within a few days for discharge that is persistent but painless, for staining that is worsening, or for any change in the shape or position of an eyelid.

Between the call and the appointment, keep the cat indoors, stop anyone rubbing or wiping the eye repeatedly, and use a soft protective collar if the cat is scratching at it. A cat can turn a small ulcer into a perforation with one hind claw.