A little crust in the corner of a cat's eye in the morning is common, and often means nothing at all. Gunk that keeps coming back, or a cat that starts holding one eye half shut, is a different story.
Cats hide discomfort well. By the time behavior changes, the eye has usually been bothering them for a while, and eye problems in cats can go from mild to serious in a day or two.
Here is how to tell ordinary tear residue from a symptom, what tends to cause the latter, and where the line sits for picking up the phone.
What ordinary looks like
Tears drain through small openings at the inner corner of each eye and down into the nose. Some always evaporate at the surface instead, leaving a trace that dries overnight.
That residue is usually a small amount, similar on both sides, and easy to lift off with a damp cloth. It often looks rusty brown or reddish rather than yellow, which surprises people, but the color comes from pigments in tears rather than from blood or infection.
Alongside it, a healthy cat's eyes look clear and glossy, open to the same width, and the cat behaves normally around light and touch. Nothing about it should make the cat hesitate or flinch.
Signs that it is not routine
Certain changes move this out of grooming territory. Any one of these is worth a call, and several together should not wait.
- Discharge that is thick, yellow, green or bloody, or that smells
- Squinting, blinking hard, a lid held partly closed, or pawing and face rubbing
- Redness or puffy swelling of the pink tissue inside the lids
- The third eyelid, the pale membrane at the inner corner, showing across the eye
- Cloudiness, a dull or hazy patch on the surface, or a visible film
- Avoiding light, hiding in dark rooms, or bumping into things
- Only one eye affected, or one eye clearly worse than the other
- Sneezing, a runny nose, poor appetite or low energy alongside the eye
A cat that suddenly cannot open an eye, an eye that has taken an obvious knock, or anything sprayed or splashed into it is an emergency. Call right away rather than waiting for office hours.
What usually causes it
The list is long, which is exactly why guessing at home rarely works. These are the ones that come up most.
Upper respiratory infections
Common feline viruses affect the eyes and the nose together, and they spread easily in shelters, multi-cat homes and among kittens. Watery eyes plus sneezing is a familiar pattern. Some of these viruses settle in for life and flare when a cat is stressed.
Conjunctivitis
Inflammation of the tissue lining the lids, from infection, irritation or allergy. The eye looks red and wet, and the cat may squint.
Scratches and ulcers on the cornea
A claw during a scuffle, a piece of grass seed, or rubbing at an already irritated eye. These hurt, and they can deepen quickly, so they are one of the main reasons not to wait and watch.
Drainage that does not work well
Flat-faced breeds such as Persians and Himalayans have crowded tear ducts and shallow eye sockets, so overflow onto the fur is normal for many of them. Blocked ducts and scarring after old infections do the same thing.
Lid and lash problems
Lids that roll inward turn fur against the eye with every blink. This is uncomfortable, constant, and does not resolve without treatment.
Irritants and allergies
Dusty litter, cigarette smoke, aerosols, cleaning sprays and scented products all sting a cat's eyes. So do drafts from a car window.
Less common but serious
Glaucoma, inflammation inside the eye, dry eye and tumors also produce discharge. Some of these threaten sight, which is another reason a veterinarian sorts this out rather than the internet.
What you can safely do at home
Cleaning is reasonable while you arrange a visit. Treating is not.
Use a soft cloth or cotton pad dampened with warm water, and wipe outward from the inner corner with a light touch. Use a fresh section for each eye so nothing travels between them. Trim long fur near the eyes only if your groomer or vet has shown you how.
Do not put anything in the eye that was not prescribed for that cat, and that includes human drops, leftover medication from another pet, saline flushes and anything containing hydrogen peroxide. Steroid drops in particular can turn a small corneal scratch into a serious problem. Wash your hands afterward, keep an affected cat away from housemates if infection is suspected, and mention any other cats when you call.
What the vet will actually do
Expect a look at the whole cat, not just the eye. A vet can numb the surface, apply a dye that lights up scratches under blue light, measure tear production, check pressure inside the eye, and look under the lids for a trapped seed or hair.
Those steps separate an irritated eye from an ulcer, and an infection from a drainage problem. Treatment follows the cause, so an accurate answer up front is what saves time, money and sometimes vision.
Common questions
Is the brown crust in the corner of my cat's eye blood?
Usually not. Tear pigment turns rusty brown as it dries. Fresh red discharge, or crust that keeps rebuilding through the day, deserves a call.
Can I catch an eye infection from my cat?
Most feline eye infections stay with cats, but a few organisms can pass to people. Wash your hands after handling the eye area and avoid touching your own eyes in between.
Can I wait a few days to see if it clears up?
Not if the cat is squinting, in pain, or the eye looks cloudy. Corneal problems worsen fast. Watchful waiting is only reasonable for a small, clear, symmetrical amount of residue in a cat who is otherwise fine.
The short version: your veterinarian is the right professional here, not a human eye doctor, and calling early is almost always the cheaper path. Describe the color, whether it is one eye or both, how long it has been going on and any squinting, since that helps them judge urgency over the phone. While the subject of eyes is on your mind, it may be a good moment to check whether your own exam has slipped past due; you can see which eye doctors accept your vision plan in a minute or two.