Most cat conjunctivitis is viral, and most simple cases settle in 7 to 10 days without anything stronger than a warm compress. Two habits decide whether a case stays simple: a fluorescein stain before the first drop, and a hard review at day 10. Skip the stain and a 1 mm corneal ulcer can melt through in 48 hours. Skip day 10 and a relapse becomes a cat that flares 4 to 6 times a year for the rest of its life.
The 3 types that cover most first visits
Vets sort by cause, not by how red the eye looks, because treatment for each type runs in a different direction. Age, which eye is affected, and the thickness of the discharge narrow most cases in under 2 minutes.
| Type | Usual trigger | Onset after exposure | Discharge | Recheck at |
|---|---|---|---|---|
| Viral (herpes, FHV-1) | Latent virus reactivated by stress, a new cat, or 2 days of boarding | 2 to 5 days | Watery, then thin mucus; 1 eye first | Day 7 |
| Bacterial, usually secondary | Damage from a virus or a scratch lets skin bacteria in | 48 to 72 hours | Thick yellow-green pus, sticks the lids shut | Day 3 |
| Chlamydial | Direct contact with an infected cat, common in shelters and catteries | 5 to 10 days | Mucoid, both eyes, lids puffy | Day 10 |
| Irritant, not infection | Litter dust, smoke, aerosol spray within 1 meter | 24 to 48 hours | Clear tears, both eyes, no pus | Day 5 |
In cats under 2 years, viral and chlamydial cases make up the large majority of first visits, and both pass to other cats in the house within 3 to 7 days of contact. If you keep 3 cats and 1 has a runny eye, assume the other 2 are incubating and wash hands between them for 10 days.
Stain first, drop second
The stain is 1 drop of fluorescein, a 60-second wait, and a blue light. Bright green uptake means the surface layer is broken, and a broken surface changes the plan: a steroid drop on an ulcer can perforate the eye in 24 to 48 hours. That single fact is why no vet should hand over a steroid-antibiotic combination for a red eye without staining it first, and why leftover drops from 6 months ago are a bad gift, whatever the label says.
Repeat the stain at every visit while the cat still squints. Ulcers can open under a lid that is healing on the outside, and the second one is often 2 to 3 times larger than the first.
The 10-day line
Viral cases peak at day 3 to 5. By day 7 the discharge should be thinner and the squint gone for most of the day. Day 10 is the decision point: discharge still present, or 2 rounds of improve-then-worsen, means the case is no longer simple. The next steps are a repeat stain, a conjunctival swab for PCR with results in 2 to 5 days, and a Schirmer tear test, where under 5 mm per minute points to dry eye and 15 mm or more is normal.
Book the review on the day you start the drops, not the day the bottle runs out. If the cat is better on day 4, keep going to day 7 anyway: stopping at the first good photo is the most common cause of a flare 48 to 72 hours later.
Home care that helps, and 3 things that hurt
A warm compress at 38 to 40 C for 2 to 3 minutes, 2 times a day, softens crusts enough to lift them with 1 wipe instead of 5. Saline at 9 g of salt per liter, 1 to 2 ml per eye, wiped from the inner corner outward, clears discharge without stinging. Use 1 cloth per eye, wash at 60 C or throw it away, because the same cloth on both eyes moves infection from the good side to the bad one within a day.
What hurts: human drops with benzalkonium preservative, which sting and sometimes contain a vasoconstrictor that hides the redness while the ulcer grows; cotton buds pressed on the cornea; and stopping treatment on day 3 because the eye looks better. Keep the room dust down, change litter to a low-dust brand, and stop spraying air freshener within 2 meters of the cat for 14 days.
Same-day visit, not tomorrow
- The cornea looks cloudy or blue-grey, or a white spot appears on it.
- Pus returns 3 or more times a day after wiping.
- Both eyes are swollen shut, or the cat will not open 1 eye at all for 12 hours.
- A kitten under 8 weeks is affected, or a pregnant queen shows any eye discharge.
- The cat stops eating for 24 hours, or the temperature passes 39.5 C.
Herpes in a kitten under 4 weeks can scar the cornea for life, and the window to reduce that damage is 24 to 48 hours, not 3 days.
What to log, and the 5-point recheck
Photograph both eyes at the same distance and light, once a day. Owners who bring 5 photos from days 1, 3, 5, 7 and 10 get a faster decision than owners who describe the eye as worse.
| Day | What happens | What decides the next step |
|---|---|---|
| 0 | Stain, photo, first drop, book the review | Green uptake means no steroid, treat the ulcer first |
| 3 | Phone check with 1 photo | Pus still thick means swab for culture |
| 7 | Second look, stain if still squinting | Quiet eye means taper over 3 to 5 days |
| 10 | Decision visit | Discharge means PCR plus tear test |
| 21 | Flare check | A second flare inside 14 days means a suppression plan |
Cost and what the visit includes
A first visit with a stain usually lands between 60 and 120 dollars. A PCR panel for herpes, chlamydia and mycoplasma runs 120 to 250 dollars and takes 2 to 7 days to come back. Drops cost 15 to 40 dollars per 5 to 10 ml bottle, and a 10-day course in a 4 kg cat uses 5 to 8 ml, so 1 bottle covers most cases.
If your cat is on long-term oral steroids for another reason, ask for a glucose check at the same visit. Steroid use raises diabetes risk, and the early signs look like a cat that drinks more because the weather turned warm. The insulin types and monitoring basics explain what the numbers mean. For a full picture of what each test costs before you agree to it, see the cost breakdown tool.
The 5-step version
- Get a fluorescein stain before the first drop, and ask for the reading in words.
- Wipe with saline and a warm compress 2 times a day, 1 cloth per eye.
- Photograph both eyes daily, and count wipes and pus episodes.
- Hold the day-10 review even if the eye looks fine on day 4.
- Go the same day for a cloudy cornea, a kitten under 8 weeks, or 24 hours of not eating.
Terms mentioned in this article
Frequently asked
Do I need a vet visit before starting eye drops?
Yes, for a first episode. A fluorescein stain takes about 60 seconds and tells you whether the cornea is intact, and that answer decides whether a steroid drop is safe. Drops given without a stain can turn a 1 mm ulcer into a perforation within 24 to 48 hours. If the eye is only watery, both sides equal, with no squint, a 24-hour wait with saline rinses is reasonable.
The eye looks better on day 3. Can I stop the drops?
Finish at least 7 days. Stopping at the first improvement is the most common reason a case flares back within 48 to 72 hours, and the second flare usually lasts longer than the first. If you want to stop earlier, ask for a recheck with a stain instead of deciding from appearance alone.
Can my other cats catch it?
Viral and chlamydial cases are contagious, and spread usually happens within 3 to 7 days of contact through tears, shared bowls, and hands. Keep the affected cat's bowls and cloths separate, wash hands between cats, and wipe surfaces for 10 days. Cats that have recovered from herpes can still shed the virus after stress, so a flare is not proof of a new infection.