When a cat squints, it usually means one of two things: the cat is communicating comfort and trust, or something is irritating or hurting its eye. The difference is easy to spot once you know what to look for. A relaxed cat that slowly narrows both eyes at you is being friendly. A cat that holds one eye partially shut, paws at its face, or squints alongside discharge or redness likely has a medical problem that needs attention.
The Slow Blink: A Sign of Trust
Cats deliberately narrow their eyes as a form of social communication. A slow blink sequence involves a series of half-blinks where the eyelids move toward each other without fully closing, often followed by prolonged narrowing or a complete eye closure. This is the cat equivalent of a relaxed smile, and it signals positive emotion.
A 2020 study published in Scientific Reports tested this directly. Cats were more likely to approach a person who had just slow-blinked at them compared to someone holding a neutral facial expression. The researchers concluded that slow blink sequences function as a form of positive emotional communication between cats and humans. If your cat squints at you softly with a relaxed body, ears forward, and no signs of distress, it’s expressing comfort. You can slow-blink back, and many cats will respond in kind.
Squinting From Eye Irritation
When squinting looks less like a lazy, contented narrowing and more like a cat struggling to keep its eye open, irritation is the likely cause. This involuntary, tight squinting is called blepharospasm, and it can affect one or both eyes. Common triggers include foreign objects stuck in or near the eye, airborne irritants like smoke or dust, bright light, and inflammation from infection or injury.
One-eye squinting is particularly telling. If your cat holds just one eye partially shut while the other looks normal, something is almost certainly wrong with that specific eye. Both-eye squinting can point to environmental irritants, allergies, or a systemic infection. In either case, the squinting itself is a protective reflex: the cat is trying to shield a painful or sensitive eye from further stimulation.
Conjunctivitis: The Most Common Culprit
Conjunctivitis, or inflammation of the tissue lining the eyelids, is one of the most frequent reasons cats squint. Along with squinting, you’ll typically see frequent blinking and discharge that ranges from clear and watery to thick and dark-colored. The conjunctiva and the third eyelid (the extra membrane cats have in the inner corner of each eye) often become swollen and red.
The overwhelming majority of feline conjunctivitis cases are caused by the cat’s own immune response to common microorganisms. The most frequent offenders are feline herpesvirus, calicivirus, and two types of bacteria. Cats with weakened immune systems are especially prone. Conjunctivitis is treatable but tends to recur in cats carrying herpesvirus, since the virus can reactivate during periods of stress.
Corneal Ulcers
A corneal ulcer is a wound on the clear surface of the eye, and it causes intense discomfort. Affected cats squint, rub their eyes, become sensitive to light, and may have cloudy discharge seeping from the eye. The cornea itself can look hazy or clouded over. Cats with corneal ulcers often behave as though they’re having trouble seeing.
Ulcers can result from scratches (fights with other cats are a common source), foreign material, chemical exposure, or infections. Veterinarians diagnose them using a fluorescent dye dropped onto the eye surface. The dye sticks to damaged tissue and glows green under a special light, making even small ulcers visible. Corneal ulcers need prompt treatment because they can deepen quickly and, in severe cases, threaten the eye itself.
Uveitis: Inflammation Inside the Eye
Uveitis is inflammation of the structures inside the eye rather than on its surface. Signs include squinting, tearing, redness, cloudiness, and visible swelling of the eye. It can be acute or chronic. In many otherwise healthy cats, the cause turns out to be immune-related, meaning the cat’s own immune system is driving the inflammation without a clear external trigger.
Chronic uveitis sometimes requires long-term medication with gradual dose adjustments over time. Left untreated, ongoing inflammation inside the eye can lead to permanent damage, including glaucoma or vision loss.
Horner’s Syndrome
Sometimes what looks like squinting is actually a drooping upper eyelid. Horner’s syndrome is a neurological condition caused by disruption of the nerve pathway that controls certain muscles around the eye. When this pathway stops working properly, the affected eye develops a narrowed appearance from a drooping lid, along with a sunken-looking eyeball and a visible third eyelid that protrudes across the inner corner.
In cats specifically, the third eyelid has smooth muscle tissue controlled by the same nerve pathway, so when the nerve signal is lost, that extra eyelid can no longer stay retracted. The result is a distinctive combination: one eye that looks half-closed, a visible third eyelid, and a pupil that appears smaller than the other eye’s. Horner’s syndrome itself isn’t painful, but it signals an underlying problem with the nerve supply that a vet needs to investigate.
Squinting as a Pain Signal
Squinting doesn’t always mean an eye problem. Cats in pain from any source, whether it’s dental disease, an injury, or internal illness, often tighten the muscles around their eyes. Veterinarians use a standardized tool called the Feline Grimace Scale to assess pain levels in cats. It scores five facial features: ear position, orbital tightening (how much the eye area is squeezed), muzzle tension, whisker position, and head posture. Each feature is rated from absent to obviously present.
Orbital tightening, the component most visible as squinting, is one of the most reliable indicators. If your cat is squinting and also has flattened ears, tense whiskers pushed forward, or a lowered head, the combination strongly suggests pain rather than a localized eye issue.
When Squinting Needs Veterinary Attention
A soft, symmetrical slow blink from a relaxed cat is normal social behavior and nothing to worry about. Everything else on this list warrants a closer look. Specific signs that point to a problem include discharge of any color, a change in pupil size between the two eyes, cloudiness or color change in the eye, redness or swelling, rubbing or pawing at the face, and squinting that persists for more than a few hours or affects only one eye.
Eye problems in cats can escalate quickly. A minor-looking squint in the morning can become a serious ulcer or a pressure buildup inside the eye by evening. All new eye changes are best evaluated sooner rather than later, since early treatment for most feline eye conditions is straightforward, while delayed treatment often means longer recovery and a higher risk of permanent damage.