Eye discharge in a cat is a symptom with about six common causes, and the colour of the discharge narrows it faster than anything else. Clear and watery points to herpesvirus or a blocked tear duct. Yellow-green and thick points to bacteria, usually sitting on top of something else. Brown staining in the inner corner of a flat-faced cat is anatomy, not infection.
Go the same day if the pupils are different sizes, the eye is cloudy, blood is visible inside the eye, the cat is holding the eye shut and rubbing it, or the eyeball looks larger than the other one. Those five signs mean glaucoma, uveitis or a deep corneal ulcer, and all of them can cost the eye within 24 to 48 hours.
Which signs are emergencies
Unequal pupils, a cloudy or blue-grey cornea, blood in the anterior chamber, severe squinting with tearing, a bulging globe, or a third eyelid that stays up over half the eye. A corneal ulcer with a melting edge is a surgical problem, not a drop problem. Herpes keratitis with a dendritic ulcer gets dramatically worse if a steroid drop is used, so no steroid goes into an eye until a fluorescein stain has been done.
Reading the discharge
| What it looks like | Most likely cause | First test |
|---|---|---|
| Clear, watery, one or both eyes | Herpesvirus, blocked tear duct | Fluorescein stain, PCR |
| Yellow-green, thick, crusting | Bacterial infection, usually secondary | Cytology and culture |
| Brown, dry, in the inner corner | Anatomy, shallow eye socket | Schirmer tear test |
| Mucoid, stringy, with red conjunctiva | Chlamydia or mycoplasma | PCR from a swab |
| Blood-tinged, with a cloudy eye | Uveitis, trauma, hypertension | Pressure check, fundoscopy |
Herpesvirus and the cornea
Feline herpesvirus (FHV-1) is the most common infectious cause of chronic eye discharge. It hides in the trigeminal ganglion and reactivates after stress, boarding, a new pet or a course of steroids. The classic lesion is a branching dendritic ulcer that only shows up under fluorescein, which is why every watery eye gets a stain rather than a guess. Most flare-ups follow a known trigger within 3 to 7 days, and about 80 percent of cats infected as kittens carry the virus for life. PCR from a conjunctival swab confirms it, though a negative swab does not exclude it.
Why lysine does not work
Lysine was recommended for years on the theory that it starves the virus of arginine. Controlled trials in cats have not shown a reduction in shedding, severity or recurrence, and current veterinary consensus is that it does not help. It is not dangerous, but it costs money and delays the antiviral that does work. Skip it and spend the money on the stain and the PCR instead.
Blocked tear ducts and chronic weeping
A cat that weeps constantly from one eye, with no squinting and no redness, usually has a blocked nasolacrimal duct, common in Persians, British Shorthairs and other flat-faced breeds whose drainage channel is compressed. Tears overflow, air and bacteria sit in the duct, and porphyrins in the tears stain the hair brown within weeks. The duct is flushed with saline under light sedation through the punctum; if a plug of mucus or a stricture is found, it is flushed until clear. Roughly 30 to 50 percent re-block within months and need a repeat, and some cats need the duct stented. Dacryocystitis — a swelling below the eye that expresses pus — needs flushing plus 2 to 4 weeks of antibiotics.
Choosing drops, and the steroid rule
Bacterial conjunctivitis is usually secondary, so the drop matters less than finding the cause. A typical choice is ofloxacin or tobramycin every 6 to 8 hours for 7 to 10 days, with recheck at day 5. For herpes, the options are idoxuridine ointment 5 times daily, or cidofovir 0.5 percent twice daily, plus oral famciclovir at 90 mg per kg twice daily in severe cases. Steroid drops are contraindicated with any corneal ulcer, with FHV-1, and in a cat whose eye pressure has not been measured. They feel good for a day and melt a cornea in a week.
Daily care that actually helps
Wipe from the inner corner outward with a warm saline-soaked pad, a fresh one per eye, twice a day. Do not use cotton buds, tap water, or human eye drops with preservatives. Keep the litter box dust-free and stop scented plugins, since both drive herpes reactivation. A cat that squints after cleaning needs a stain, not more cleaning.
Five steps for this week
- Photograph both eyes in daylight, then again in 48 hours, so change is measurable.
- Book a visit that includes a fluorescein stain, a Schirmer tear test and eye pressure.
- Stop any steroid drop immediately and do not restart without a stain.
- Ask for a conjunctival PCR if discharge has lasted more than 3 weeks.
- Keep a note of every episode with its date and trigger, because herpes recurrence patterns are what guide long-term control.
Discharge with sneezing, fever or loss of appetite is usually the eye end of a whole upper respiratory infection, covered in cat URI symptoms, and the herpes and calici components are why the kitten series in feline vaccine schedule matters. A cat that stops eating because it cannot smell is a separate problem, handled in cat not eating.
Frequently asked
My cat has had a watery eye for months. Is that serious?
Usually not an emergency, but it is not nothing. A single weeping eye with no squinting or redness is most often a blocked nasolacrimal duct, which is common in flat-faced breeds and can be flushed under light sedation. It should still be examined once, because a low-grade herpes infection and a foreign body under the third eyelid look similar from the outside.
Can I use my own antibiotic eye drops on the cat?
No. Human drops often contain preservatives and sometimes a steroid, and steroid drops on a corneal ulcer can melt the eye within days. Even a plain antibiotic drop treats the symptom while the herpes or the blocked duct continues. The first step is always a fluorescein stain to see whether the cornea is intact, then the drop that matches the cause.
Does lysine prevent herpes flare-ups?
The evidence says no. Lysine was used for years on the theory that it deprives the virus of arginine, but controlled trials in cats have not shown less shedding, milder signs or fewer recurrences, and current consensus is that it does not help. Managing stress, keeping the litter dust-free and treating flares early with an antiviral does more than any supplement.