A cat that squints one eye is in pain, not being dramatic. The cornea is about 0.6 mm thick at the center, and a surface defect can become a deep ulcer, a melting ulcer, or a perforation within 24 hours. That is why this symptom gets a same-day slot.
Squinting, tearing, and a held-shut lid look alike across 6 problems: ulcer, uveitis, glaucoma, entropion, foreign body, herpesvirus flare. They need opposite treatments, so the first visit is about tests, not drops.
Why 24 hours decides the outcome
The cornea has no blood vessels, so it heals from the edges and the tear film, with no reserve thickness to lose. A superficial ulcer that stains without pitting closes in 3 to 7 days with the right drops. One that has lost 30 to 50% of stromal depth in 24 to 48 hours is a different case, and a melting ulcer with a gelatinous grey edge can perforate in under 24 hours. Depth, not size, sets the clock.
Two things speed that up. A steroid drop on an unsuspected ulcer can thin the cornea within 48 hours. A dry eye with a Schirmer tear test under 15 mm per minute in a cat, or under 10 mm in a sedated one, heals far more slowly and needs tear support from day 1.
The 2-minute stain test is the first step, not the last
Fluorescein takes about 2 minutes: 1 drop, a saline flush after 60 seconds, then a cobalt blue light. Green uptake means the surface is broken, and the shape tells the vet whether it is a scratch, a herpesvirus patch, or a melting edge. No home substitute exists. Do not use human eye drops before the visit: a steroid changes what the stain shows and can worsen a melting ulcer.
Pressure above 25 mmHg changes the plan
Normal feline intraocular pressure reads 15 to 25 mmHg, and most healthy cats sit at 15 to 22. Above 25 in a squinting eye with a dilated pupil and a cloudy cornea points to glaucoma, which hurts and can blind an eye in 24 to 72 hours. A gap of 5 mmHg or more between the 2 eyes is abnormal even when both numbers look fine. Tonometry takes about 1 minute per eye and belongs in the first visit for any red or cloudy eye.
Five signs that move the visit to today
These 5 findings are the ones most likely to mean surgery or a specialist rather than drops. Any single one is enough.
| Sign | Threshold | What it suggests | Act within |
|---|---|---|---|
| Pupil stays wide in bright light | no constriction at 10 seconds | glaucoma or retinal disease | 6 hours |
| Eye pressure | above 25 mmHg, or 5 mmHg side difference | glaucoma | 6 hours |
| Cloudy or grey cornea | haze over 30% of the surface | deep ulcer, edema, or melting | 12 hours |
| Dark spot on the cornea | any, 1 mm or larger | sequestrum, or a foreign body | 7 days, 24 if painful |
| Pus in the front chamber | any visible white layer | uveitis or infection | 6 hours |
What you can check at home in 3 minutes
Do this before you call, and photograph it in daylight without flash, since flash washes out the cloudiness. Wash your hands first and do not touch the eye.
- Compare both eyes from 30 cm in normal light: constant squint, or does it come and go over 5 minutes?
- Check discharge on a tissue: clear suggests tear or ulcer, yellow-green suggests infection, dark brown crust in a flat-faced cat suggests a blocked tear duct.
- Shine a phone light from 20 cm at a 45 degree angle: a pupil that shrinks within 10 seconds is reacting, one that stays wide is not.
- Count 1 minute of blinking: over 20 blinks a minute, or a lid shut for 30 seconds, is significant.
- Check the third eyelid: a pink membrane covering more than 3 mm of the eye corner points to pain, dehydration, or Horner syndrome.
When to book, by the hour
2 hours: the eye is bulging, the pupil is fixed wide, or the cat paws at the face and cries. Treat that as glaucoma or a perforation. 6 hours: sudden cloudiness, a white layer inside the eye, or squinting that began after a fight or fall. 12 hours: a squint that appeared today with discharge, or a cat that will not open the eye. 24 hours: a squint present for 24 hours without improvement, even if the cat eats. 48 hours: recheck of a treated superficial ulcer, restained at 48 hours and again at 5 to 7 days until the dye stays clear.
If the squint followed contact with a plant, a cleaning spray, or a diffuser, check the toxic list before you wait, because chemical burns progress in the first 6 hours.
What to record for the vet
Eight lines, morning and night, save a repeat visit and make a 3-day trend visible.
- Which eye, and the clock time the squint was first seen.
- Blink count in 1 minute, at both checks.
- Discharge color and amount, described in 1 word plus a photo.
- Whether the third eyelid is visible, and how many mm.
- Pupil size in the same light, noted as small, medium, or wide.
- Appetite in grams, and whether the cat is eating with the head tilted.
- Any sneezing or nasal discharge, since herpesvirus runs with both.
- A photo at the same distance and light, once daily, without flash.
What not to do while you wait
Do not use a leftover steroid drop: on an ulcer it thins the cornea inside 48 hours. Do not use a human red-eye drop, since the vasoconstrictor hides the redness that guides the exam. Do not flush with contact lens solution or tap water; both add bacteria. Do not wait for the eye to open on its own in a cat over 12, since uveitis and lens problems are far more common in old cats than in kittens. Keep the cat indoors and stop rubbing with a soft cone, not a bandage.
Five steps for today
- Photograph both eyes in daylight without flash, from 30 cm.
- Count blinks for 1 minute and write the number down.
- Call the clinic and say how many hours the squint has been present.
- Ask for a fluorescein stain and a pressure reading at the first visit, not the second.
- Book the 48-hour recheck before you leave, and keep the cone on until then.
A swollen or fully closed eye is a related but different pattern, covered in eye swelling, and a grey or white film that builds over weeks is covered in cloudy eye.
Terms mentioned in this article
Frequently asked
My cat is squinting but still eating. Can I wait until Monday?
If the squint has been there 24 hours, no. Appetite is a poor guide to eye pain, because cats eat through corneal ulcers. A surface defect can deepen to a melting ulcer in under 24 hours, and pressure above 25 mmHg can blind an eye in 24 to 72 hours. Call and describe how many hours the squint has been present, not how the cat seems.
What does the fluorescein test actually show?
It shows where the corneal surface is broken. One drop, a saline flush after about 60 seconds, and a cobalt blue light take roughly 2 minutes, and green uptake marks the defect. The pattern separates a scratch from a herpesvirus patch or a melting edge, which is why the stain plus a pressure reading drives the treatment plan.
Are human eye drops safe for a squinting cat?
No. A steroid drop on an undetected ulcer can thin the cornea within 48 hours, and a vasoconstrictor hides the redness the vet needs to see. Flushing with tap water or contact lens solution adds bacteria. Keep the eye clean with sterile saline if you must, use a soft cone, and let the clinic stain and measure pressure first.
Related guides
- Cat Eye Bulging Out: Minutes, Not Hours
- Cloudy Eye in a Cat: Edema, Cataract or Glaucoma
- Cat Eye Swollen Shut: 4 Causes and the 2 Tests
- Prolapsed Eye in a Cat: First 10 Minutes, Then Surgery
- Eye Injury in Cats: Ulcers, Stains, and the 24-Hour Window
- Cat Eye Discharge: Herpes, Blocked Tear Duct, or Emergency