Cats get eye infections through a handful of common routes: viral exposure, bacterial transmission, physical injury to the eye, and anatomical traits that leave certain breeds more vulnerable. Most feline eye infections trace back to just two viruses, and many cats carry one of them for life without their owners ever knowing.
Viral Infections Are the Most Common Cause
Feline herpesvirus (FHV-1) and feline calicivirus together account for the majority of respiratory and eye infections in cats. Calicivirus alone causes roughly half of all feline respiratory infections, with herpesvirus responsible for much of the rest. Sometimes both viruses strike at the same time.
Herpesvirus is the bigger concern for the eyes specifically. It targets the cornea and surrounding tissues, causing inflammation, ulcers, and heavy discharge from the eyes and nose. Almost all cats that recover from an active herpesvirus infection become lifelong carriers. The virus hides in nerve tissue and can reactivate during periods of stress, illness, or immune suppression, triggering a new round of eye symptoms weeks, months, or even years later. This is why some cats seem to get recurring eye infections throughout their lives.
Both viruses spread through direct contact with infected saliva, nasal secretions, or eye discharge. They also spread indirectly through contaminated objects like food bowls, bedding, and litter boxes. A sneeze from an infected cat can send virus-laden droplets several feet.
Bacterial Infections: Primary and Secondary
Two bacteria deserve special mention. Chlamydia felis is the most common bacterial cause of conjunctivitis in cats, particularly in kittens under nine months old. It produces a distinctive pattern: the infection typically starts in one eye, then spreads to the other within days. You’ll notice swelling of the conjunctiva (the pink tissue lining the eyelids), squinting, and discharge that starts clear and watery before turning thick and yellowish-green. Unlike herpesvirus, chlamydial infections rarely cause corneal ulcers, and respiratory symptoms tend to be minimal.
Mycoplasma is another bacterium that infects feline eyes, though it’s less common as a standalone cause. More often, bacteria like these move in as secondary invaders after a virus has already weakened the eye’s defenses. A cat fighting off herpesvirus, for instance, has damaged and inflamed tissue that bacteria can colonize easily. This layering of infections is why a cat’s eye discharge sometimes shifts from watery to thick and colored over the course of an illness. That color change often signals bacterial involvement on top of a viral infection.
Physical Injury and Irritants
Not every eye infection starts with a pathogen. Physical damage to the cornea creates an entry point for bacteria that would otherwise never cause a problem. Common causes of corneal injury include scratches from fights with other cats, a piece of dirt or debris trapped under the eyelid, ingrown eyelashes rubbing against the eye surface, and exposure to caustic chemicals like household cleaners.
These injuries can develop into corneal ulcers, which are essentially open wounds on the eye’s surface. Left untreated, bacteria colonize the damaged tissue and the ulcer deepens. Cats also tend to paw at painful eyes, which introduces more bacteria and worsens the damage. This cycle of injury, infection, and self-trauma is why vets often send cats home with a cone collar until the eye fully heals.
Why Flat-Faced Breeds Are More Vulnerable
Persian cats and other flat-faced breeds face a structural disadvantage. Their shortened skulls create shallow eye sockets, which means their eyes sit further forward and protrude more than in other breeds. This anatomy, known as brachycephalic ocular syndrome, creates several compounding problems.
The eyelids often can’t close completely over the protruding eyes, leaving parts of the cornea permanently exposed to air and drying out. The eyelid openings may be oversized, exposing the whites of the eyes. Some of these cats also develop inward-rolling eyelids or prominent nasal skin folds that push hair directly against the cornea, causing constant irritation. All of this makes the corneal surface fragile and prone to ulcers, which can quickly become infected, deepen, and in severe cases threaten the eye itself.
Newborn Kittens Face Unique Risks
Kittens are born with their eyelids sealed shut, and they don’t open until around 10 to 14 days of age. If bacteria or herpesvirus reach the eye during this window, infection develops behind the closed lids where it can’t drain. Thick pus builds up in the sealed space, pressing against the cornea.
The most common route of infection is passage through the birth canal of a mother carrying bacteria like Staphylococcus, Streptococcus, or Chlamydia. Herpesvirus can also pass from an infected mother through direct contact with her secretions. Because the trapped pus has nowhere to go, neonatal eye infections cause damage fast. The conjunctiva can adhere directly to the cornea, and scarring can become permanent. Corneal rupture and blindness are real possibilities if the infection isn’t caught early.
How to Read the Discharge
The appearance of your cat’s eye discharge offers clues about what’s going on. Clear, watery discharge typically signals the early stages of a viral infection or an allergen irritating the eye. Cloudy, yellow, or greenish discharge points toward bacterial involvement, either as the primary infection or riding on top of a viral one. Redness of the tissue lining the eyelids accompanies both types.
One-sided discharge that later becomes two-sided is a hallmark of chlamydial infection. Corneal ulcers from herpesvirus or injury often cause the cat to hold the affected eye shut and avoid light. If you notice the eye itself looking cloudy or hazy rather than just the discharge, that suggests the cornea is involved, which is more serious than surface-level conjunctivitis alone.
Environments That Raise the Risk
Any setting where cats are housed in close quarters dramatically increases the chance of eye infections. Shelters, catteries, and multi-cat households see higher rates because the viruses and bacteria responsible spread so easily through shared air, shared surfaces, and direct contact. Stress from crowding also suppresses the immune system, which can reactivate latent herpesvirus in carrier cats and spark outbreaks.
Outdoor cats face higher exposure to fight injuries and contact with infected strays. Indoor cats in single-cat homes have the lowest risk overall, though a cat carrying latent herpesvirus can develop eye infections without any new exposure, simply from stress triggers like a move to a new home, the introduction of a new pet, or a bout of another illness.