A cat squinting both eyes is usually a sign of contentment. A cat squinting just one eye is a different story. That asymmetry matters more than most cat owners realise, and understanding what’s behind it can make a real difference to whether your cat keeps their vision.

Single-eye squinting is almost always a sign that the eye is sore. The cause might be something relatively minor, like an infection, or it could be something more serious, like a foreign object lodged in the eye or internal inflammation linked to illness elsewhere in the body. The tricky part is that you often can’t tell which from looking at it. What the causes have in common is that they all need veterinary attention, and most get worse the longer they’re left.

What You’re Actually Looking At

Cat eyes work similarly to human eyes, but with a few differences worth knowing. The pupil, the dark centre of the eye, is slit-shaped rather than round. In bright light, it should narrow to a thin line; in darkness, it dilates to nearly a full circle. If your cat’s pupil stays large in bright light or stays narrow in the dark, something may be off.

The coloured ring around the pupil is the iris, which in cats comes in greens, blues, yellows, and oranges. If the iris changes colour or the blood vessels within it become more noticeable, that can signal illness. The white area around the eye is called the sclera, and like the iris, changes in colour or visible blood vessels there are worth flagging to a vet.

Cats also have a third eyelid, a pale pink membrane that normally sits tucked in the corner of the eye closest to the nose. When an eye is injured or inflamed, this third eyelid can move across to partially or fully cover the eye’s surface. If you can see it, the eye is almost certainly sore.

The Most Common Reasons Cats Squint One Eye

Trauma is one of the leading causes. Outdoor cats are more exposed to this through fights with other cats or wildlife, but indoor cats can injure an eye by running into furniture or catching a claw on something. You might see discharge from the eye, which can be watery or thick and yellow-green, along with redness, swelling, or what looks like a small dent on the surface of the eye. Injuries like this can worsen quickly if they become infected, so a same-day vet visit is the right call.

Eye infections are also common. These are usually viral, bacterial, or a combination of both. Viral infections such as cat flu can be caught from other cats or can reactivate from a virus your cat already carries, often triggered by stress or illness. The signs look similar to trauma: discharge, redness, swelling, and a visible third eyelid. A viral infection may also cause sneezing alongside the eye symptoms.

Foreign bodies are less common but cause some of the most urgent cases. Thorns, grass awns, and cat claws are among the things that can become trapped in a cat’s eye. Sometimes you can see the object, but often it’s hidden under the eyelid. A cat with something stuck in their eye is typically in significant pain and may refuse to open the eye at all. This is an emergency. Delays risk permanent damage, potential blindness, or in severe cases, surgical removal of the eye.

Entropion is a condition where one eyelid, usually the lower one, rolls inward. The hairy skin then rubs against the eye’s surface, which is painful and can cause damage and infection over time. It can affect cats of any age and generally requires surgery to correct.

Finally, uveitis is inflammation inside the front of the eye, between the cornea and the iris. This one stands out because it can be a sign that something is wrong elsewhere in the body entirely. Conditions such as severe infections, cancer, diabetes, high blood pressure, and autoimmune disease can all cause uveitis. The eye may look cloudy or hazy, and sometimes the bottom of the eye fills with sediment that appears red, white, or yellow. Unlike most other causes of squinting, there’s often no discharge. Any cat suspected of having uveitis should be seen promptly, as the underlying cause needs to be found and treated.

When It’s an Emergency

Some cases of a squinting eye need same-day emergency treatment. Call your vet immediately if:

Your cat’s eye appears dented or damaged on the surface, you can’t see the eye at all beneath the swelling, you think something may be trapped inside the eye, your cat won’t stop rubbing at it, or your cat seems withdrawn or is showing other signs of illness alongside the eye symptoms.

What You Can Do at Home

If your cat’s eye is weeping or has discharge building up around it, you can gently clean the area to keep it comfortable. Boil some water, let it cool completely, then use a clean cotton cloth to wipe softly around the eye. This won’t fix the underlying problem, but it can provide temporary relief and prevent the discharge from crusting.

One important rule: if you suspect something is trapped in the eye, don’t attempt to clean it or remove the object yourself. You risk making things significantly worse. Get to a vet instead.

It’s also worth knowing that you shouldn’t wait to see if a sore eye resolves on its own. Some minor injuries do heal without treatment, but it’s impossible to distinguish those from more serious damage at home. Either way, your cat will be in pain, and a vet can provide relief and check for any deeper problems. Eye issues can deteriorate quickly, and the sooner they’re treated, the better the chances of protecting your cat’s vision.

Featured Image Credit: Adina Voicu, Pixabay

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