A cat that squints is almost always experiencing eye pain or irritation. Unlike the relaxed half-closed eyes of a content cat or the slow blink that signals affection, medical squinting is persistent, often affects one eye more than the other, and may come with tearing, discharge, or visible redness. The underlying cause can range from a minor irritant to a serious infection, so the pattern and accompanying symptoms matter.
Relaxed Blinking vs. Pain Squinting
Cats naturally narrow their eyes when they feel safe and comfortable. A slow, deliberate blink directed at you is a social gesture, sometimes compared to a cat’s version of a smile. This looks very different from medical squinting. A cat in pain will hold one or both eyes partially shut for extended periods, flinch away from light, paw at its face, or keep the third eyelid (a pale membrane in the inner corner) visibly raised. If the squinting comes and goes only when your cat is relaxed on your lap and there’s no discharge or redness, it’s likely just contentment. If it persists when your cat is active and alert, something is wrong.
Conjunctivitis: The Most Common Cause
Inflammation of the tissue lining the eyelids is the single most frequent reason cats squint. You’ll usually see watery or mucus-like discharge, redness around the eye, and swelling of the surrounding tissue. In cats, conjunctivitis is rarely caused by allergies, despite how common that cause is in people. Instead, it’s usually driven by one of three infections: feline herpesvirus, chlamydia, or mycoplasma bacteria.
Feline herpesvirus (FHV-1) deserves special attention because it’s extremely common. Most cats are exposed as kittens, and the virus then hides in the body permanently. Stress, illness, or a weakened immune system can reactivate it at any point in life, causing a flare-up of conjunctivitis, sometimes with corneal ulcers. During active infection, the virus destroys the surface cells of the conjunctiva and cornea, which is what makes the eye painful and causes the squinting. Flare-ups often affect both eyes and produce a watery discharge that can turn thick and yellowish over time.
For straightforward bacterial conjunctivitis, most vets prescribe antibiotic eye drops or ointment applied three or four times daily. The discharge and squinting typically clear up within two to three weeks. Herpesvirus-related cases take longer and may require antiviral medication for around 21 days.
Corneal Ulcers and Scratches
The cornea is the clear outer surface of the eye, and it’s vulnerable to scratches from rough play, fights with other cats, or contact with plant material. A cat with a corneal ulcer will squint, shy away from bright light, produce excessive tears, and sometimes paw at the affected eye. You may notice the eye looks cloudy or hazy. Cornell University’s Feline Health Center notes that an affected cat often behaves as if it’s having trouble seeing.
In cats, corneal ulcers caused by bacteria alone are uncommon. The more typical scenario is either physical trauma (a scratch or a foreign body stuck under the eyelid) or herpesvirus reactivation, which creates a distinctive branching pattern of damage on the corneal surface. Regardless of cause, corneal ulcers are considered urgent. Without treatment, a small ulcer can deepen and expand, potentially leading to permanent scarring or even loss of the eye.
Diagnosis is straightforward. Your vet will apply a drop of fluorescein dye to the eye’s surface. The dye sticks to any damaged tissue and glows green under a blue light, making even tiny ulcers clearly visible. This test takes seconds and doesn’t require sedation.
Uveitis: Inflammation Inside the Eye
When the inflammation is deeper, affecting the colored part of the eye (the iris) and surrounding internal structures, it’s called uveitis. This is one of the more serious causes of squinting in cats. Along with holding the eye shut and tearing, you might notice a change in iris color, a pupil that looks unusually small, or cloudiness within the eye itself. Some cats develop visible blood or a cloudy layer of fluid inside the eye.
Uveitis has a long list of potential triggers, including infections like feline leukemia virus, feline immunodeficiency virus, feline infectious peritonitis, and toxoplasmosis. It can also result from trauma, immune system disorders, or tumors within the eye. In about 70% of cases, no specific cause is ever identified. Left untreated, uveitis can lead to glaucoma, cataracts, retinal detachment, or permanent vision loss.
Glaucoma and Eye Pressure
Glaucoma occurs when fluid pressure inside the eye rises too high and begins damaging the optic nerve. Normal eye pressure in cats averages around 12 mmHg, and readings of 25 mmHg or higher in an older cat warrant investigation. Interestingly, cats with glaucoma often show surprisingly little obvious discomfort compared to dogs or humans with the same condition. They may maintain a normal appetite and activity level even when pressure is significantly elevated. Squinting, when present, tends to appear only when pressure spikes sharply. More subtle signs include a dilated pupil that doesn’t respond normally to light, or one eye that looks slightly larger than the other over time.
Flat-Faced Breeds Are at Higher Risk
Persians, Himalayans, Exotic Shorthairs, and other flat-faced breeds have a structural disadvantage. Their eyes sit farther forward in the skull, and their eyelids often can’t close completely. This incomplete closure, called lagophthalmos, means the cornea dries out more easily and is more exposed to injury. Some of these cats also have inward-rolling eyelid edges or prominent skin folds near the nose that cause fur to rub directly against the eye’s surface. Compounding the problem, flat-faced cats often have reduced corneal sensitivity and blink less frequently, so they may not show pain even when a serious problem is developing. If you have a brachycephalic cat, even mild redness or squinting is worth having checked.
Signs That Need Prompt Attention
Some symptoms alongside squinting signal a problem that can worsen quickly:
- Pupils of different sizes can indicate nerve damage, uveitis, or glaucoma
- Sudden cloudiness or color change in the eye suggests inflammation or fluid buildup inside the eye
- Visible third eyelid that stays raised across part of the eye points to pain or neurological involvement
- Thick yellow or green discharge suggests bacterial infection that needs treatment
- Bumping into objects or missing jumps indicates vision loss, which can become permanent if the underlying cause isn’t addressed quickly
A cat squinting in one eye only is more likely dealing with a local problem like a scratch, ulcer, or foreign body. Squinting in both eyes leans toward a systemic infection or irritant exposure. Either way, squinting that lasts more than a few hours, gets worse, or comes with any discharge beyond occasional clear tearing is not something that resolves on its own. Eye conditions in cats tend to escalate rather than improve without intervention, and early treatment almost always means a faster recovery and a better outcome for your cat’s vision.