Cat Eye Swollen Shut: 4 Causes and the 2 Tests

An eye swollen shut is 1 of the few cat problems where the clock runs in hours, not days. Four conditions cover most of it: conjunctivitis, corneal ulcer, periocular cellulitis, and glaucoma. Two exams separate them, a fluorescein stain and a pressure reading, and both take under 10 minutes. A cat that cannot open the eye for 4 hours, or has a hard eyeball, needs that exam today.

The 4 causes side by side

Cause	What you see	Key test	Visit within
Conjunctivitis	Red lids, 1 to 3 mm of discharge, eye still opens halfway	Stain to rule out ulcer	48 hours
Corneal ulcer	Squinting, tearing, 1 to 4 mm cloudy spot, blue-grey haze	Fluorescein stain, cobalt light	24 hours
Periocular cellulitis or abscess	Puffy lids 3 to 8 mm thick, fever 39.5 to 40.5 C, pain on touch	Temperature, exam, sometimes ultrasound	12 hours
Glaucoma	Hard globe, pupil 6 to 8 mm and fixed, eye pressure 40 to 60 mmHg	Tonometry, normal 15 to 25 mmHg	6 hours
Foreign body under the lid	Tearing from 1 eye, rubbing with 1 paw, no fever	Stain plus lid flip	24 hours
Herpesvirus conjunctivitis	Both eyes, 1 to 2 mm clear discharge, sneezing in the same week	Exam, stain to exclude ulcer	72 hours

The single most useful number in that table is the pressure reading. A cat eye at 15 to 25 mmHg is comfortable; at 40 mmHg the retina starts to lose cells within 24 to 48 hours, and at 60 mmHg the eye can be blind in 12 to 24 hours even though it still looks open.

Conjunctivitis: red lids, mild swelling

Simple conjunctivitis swells the lids by 1 to 2 mm, leaves the eye half open, and produces 1 to 3 mm of discharge at the inner corner. Herpesvirus is the usual cause when both eyes are involved and the cat also sneezes. Most vets treat it with 4 to 6 lubricant drops a day plus a saline wipe 2 to 3 times daily, and add an antiviral only when the cornea is also involved.

Never start a steroid drop on a red eye before a stain. A 1 percent steroid drop on a 2 mm ulcer can melt the cornea through in 24 to 48 hours, and that is the difference between 5 days of drops and a graft.

Corneal ulcer: the stain decides

A 1 to 4 mm ulcer looks like a small cloudy spot, and the cat keeps the eye shut because every blink hurts. The stain is 1 drop of fluorescein, a 30-second wait, then a cobalt blue light: damaged cornea glows green, and a 2 mm lesion is obvious. A deep ulcer that is 50 percent or more of the corneal thickness needs a specialist the same day, because the eye can rupture in 24 hours.

What you must not do is the part owners get wrong most often. No steroid drops, no human antibiotic ointment, and no chamomile tea. Flush with 0.9 percent saline if there is grit in the eye, then leave it alone until the stain. Signs that the ulcer is getting worse rather than better: the cloudy area doubles in 24 hours, the eye starts to bulge, or the pupil becomes 6 mm and fixed.

Periocular cellulitis: swelling with fever

Cellulitis thickens the lids by 3 to 8 mm, so the eye disappears behind tissue instead of simply squinting. The tip-off is the temperature: 39.5 to 40.5 C together with a cat that flinches when you touch the side of its face. An abscess behind the eye pushes the globe forward 2 to 5 mm and can be mistaken for a tumor. Most vets drain and start antibiotics within 12 hours, because infection behind the eye can track to the brain case in 48 to 72 hours.

Dental disease is the common trigger. An upper carnassial tooth root sits 3 to 5 mm from the orbit, and 1 infected root is enough to swell the whole side of the face. If the cat has 2 or more weeks of bad breath, the mouth needs a look at the same visit.

Glaucoma: hard eye, wide pupil

Glaucoma is the emergency in this list. The globe feels like a marble, the pupil sits at 6 to 8 mm and does not react to light, and the surface looks cloudy within 24 to 48 hours. A pressure of 40 mmHg or more needs treatment the same day; 60 mmHg and above can cost the eye in 12 to 24 hours. Cats hide it well, so a single episode of 5 minutes of pawing at the face with 1 eye half closed is worth a pressure check.

Do not wait for the eye to look bad. Sight loss from glaucoma is permanent once the retina is damaged, and 1 blind eye is a 50 percent risk for the other one within 2 to 3 years, so the good eye gets checked every 6 to 12 months from then on.

The 4 signs that mean go within 24 hours

• The eye stays shut for 4 hours or more, or the cat cries when the lid is lifted.
• The eyeball is hard, or 1 eye looks larger than the other by 2 mm or more.
• A cloudy or white patch appears, or the eye starts to bulge past the lids.
• Fever above 39.5 C, or the cat stops eating for 24 hours.

Two more situations skip the waiting room. First, an eyeball that has come out of the lids is a surgical emergency within 6 to 12 hours, and the tissue must stay moist with saline on the way. Second, any trauma, cat fight, or chemical splash in the last 24 hours, including a cleaning spray or an essential oil diffuser, means flush for 15 minutes with saline and call the vet, then check the toxin list for what was on the fur.

What to do in the first 2 hours

Keep the cat in a dim room, because a sore eye that is exposed to full light stays clamped. Wipe the closed lid from the inner corner outward with 0.9 percent saline on gauze, 1 wipe per swab, 3 to 4 swabs, and do not press on the globe. A cone stops 1 paw from doing in 10 seconds what 3 days of drops cannot fix. Photograph both eyes from 30 cm in the same light every 6 hours so the 2 mm difference is visible later.

Discharge that is clear and 1 to 3 mm wide is often the start of a viral problem, and the discharge guide covers the day-by-day pattern. If the third eyelid is up across both eyes, that is a different emergency picture and the prolapse page covers what to do before the car ride. Bring the cat in with the eye still closed rather than prying it open in the parking lot: 1 wrong squeeze on a 40 mmHg globe can be the difference between drops and surgery.

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