When to see a vet urgently
Take your cat for prompt examination if it develops:
- holding an eye closed, marked squinting or obvious eye pain;
- corneal cloudiness or rapid changes to the eye's surface;
- sudden deterioration in vision or bumping into things;
- eye symptoms with loss of appetite or a marked decline in general condition.
The 2–3-week duration mentioned above does not mean a symptomatic eye can be left unexamined until then. You can find a vet near you.
Overview
The conjunctiva protects the eye by moistening it and helping prevent pathogens entering. Chronic inflammation changes its structure: the membrane thickens, blood vessels dilate, and discharge and irritation develop. In cats, it often accompanies chronic respiratory infections involving FHV-1, FCV or Chlamydia felis, or occurs as an independent eye problem.
The conjunctiva differs from the cornea, the transparent surface at the front of the eye. It also covers the third eyelid visible at the inner corner. Redness and swelling there can therefore be prominent during inflammation. Conjunctival inflammation alone and a concurrent corneal ulcer require different assessment.
Persistent symptoms may represent continuous inflammation or separate recurrent episodes. Herpesvirus can remain dormant in the body and reactivate later, for example during stress or another illness. A new episode therefore does not always mean a new infection. Conversely, not every eye symptom in a herpesvirus carrier is automatically caused by the virus.
Causes
- Viral infections, including herpesvirus, FHV-1, and calicivirus, FCV.
- Bacterial infections, including chlamydia, mycoplasmas and secondary bacteria.
- Allergic reactions to dust, pollen, household chemicals or food.
- Structural factors, including inward-turning eyelids and eyelash abnormalities.
- Systemic conditions, including weakened immunity and chronic infections.
The list describes possible underlying factors; redness alone cannot establish allergy or food involvement. A retained foreign body, tear-film disturbance or persistent eyelid rubbing can sustain symptoms. If only one eye has long-term signs, local irritation is investigated particularly carefully.
Chlamydia felis can cause prolonged conjunctivitis without marked respiratory signs. Symptoms may begin in one eye and spread to the other. Several pathogens can coexist in one cat. Pus-like discharge alone does not show whether bacteria are the primary cause or a secondary infection follows damage from something else.
Risk factors
- Kittens and young cats.
- Unvaccinated cats.
- Cats in rescue shelters and breeding establishments, with high viral infection risk.
- Cats with chronic respiratory disease.
- Flat-faced breeds, such as Persians and Exotic Shorthairs, because of eye structure.
A vaccinated adult cat can also become ill. Vaccination reduces symptom severity for some infections but does not prevent every infection or eliminate herpesvirus carriage. Structural causes are independent of vaccination. Simultaneous symptoms in household cats are relevant history, but an individual case may also result from local eye disease.
Typical symptoms
Chronic conjunctivitis in cats causes:
- redness and swelling of the eye's mucous membrane;
- persistent tearing;
- mucoid or pus-like discharge;
- eyelids sticking together, especially in the morning;
- light sensitivity;
- corneal cloudiness or ulcers with herpesvirus;
- itchy eyes, with the cat rubbing its face with its paws.
Watch whether one or both eyes are affected, whether discharge is constant and whether the cat keeps an eye closed more than usual. Also report sneezing, nasal discharge and previous eye medicines. A photograph may help describe intermittent changes but does not replace examination or show an ulcer's depth.
Corneal cloudiness or an ulcer is not ordinary, harmless conjunctival redness. Pain, light sensitivity and vigorous eye rubbing particularly may reflect corneal damage or inflammation inside the eye. Little discharge does not rule out a serious eye problem.
Complications and consequences
Untreated chronic conjunctivitis can lead to:
- conjunctival scarring;
- adhesions between the conjunctiva and cornea;
- corneal ulcers and cloudiness;
- impaired or lost vision;
- spread of infection to other eye structures.
The risk of visual damage depends on the underlying disease and whether the cornea or internal eye structures are also affected. Not every red eye leads to blindness, but appearance alone cannot confirm that waiting is safe. Recurrent corneal damage needs its own plan as well as relief of conjunctival symptoms.
Diagnosis at the vet
Diagnosis uses:
- an eye examination;
- conjunctival swabs and PCR for FHV-1, FCV, Chlamydia felis and Mycoplasma;
- bacterial culture of discharge;
- a Schirmer tear test to assess tear production;
- fluorescein staining to check for corneal ulceration.
Examination also checks eyelid position, the eye's surface and possible foreign bodies. Eye pressure may be measured alongside tear production if findings suggest another eye disease. Fluorescein staining reveals corneal surface damage that may not be visible to the naked eye. Treatment is therefore not chosen from discharge colour alone.
PCR examines a sample for a pathogen's genetic material. A positive herpesvirus result alone does not confirm that it causes current signs: low-level shedding may also explain it. The result is interpreted alongside symptoms, findings and sampling technique. Testing for chlamydia needs a good sample containing mucosal cells because the bacterium lives inside cells.
If ordinary treatment fails or tissue looks unusual, cytology or biopsy may be needed. One possible separate disease is eosinophilic keratoconjunctivitis, inflammation of the cornea and conjunctiva associated with particular inflammatory cells. Raised pale or pink areas may appear, and cytology helps diagnosis. Persistent redness is therefore not always the same infectious disease.
Treatment
Treatment depends on the cause and corneal condition. Bacterial inflammation may need antibiotics, herpesvirus may need antiviral medication, and a structural problem may require corrective treatment. Antibiotics do not eliminate herpesvirus carriage. For chlamydia, systemic antibiotics may be more effective than eye drops alone, and the treatment needs of other contact cats are also assessed.
Do not start corticosteroid-containing eye drops yourself. They can delay corneal ulcer healing and worsen a herpesvirus-related problem. However, some specifically diagnosed inflammatory diseases may require anti-inflammatory or immunosuppressive treatment. This needs diagnosis, ulcer assessment and monitoring; the same medicine does not suit every red eye.
Discuss whether medication can be given successfully at the appointment. If you cannot administer drops or your cat strongly resists, explain so the plan can be changed safely. Treatment also depends on whether disease is confined to the eye's surface or involves other signs. Do not use a previous episode's prescription as instructions for new symptoms without assessment.
Home care and monitoring
Gently clean discharge around the eye as the practice advises. Wash your hands before and after handling it. Do not let the dropper tip touch the eye, eyelids or another surface. Use only an eye product prescribed for that cat; a skin cleanser is unsuitable for the eye.
Follow the individual instructions for medication administration and treatment duration. Rapid symptom relief alone does not show that infection or a possible ulcer has healed. An agreed check-up may include repeat staining. If the eye becomes markedly redder or is rubbed more after medication, contact the practice before continuing.
Prevent rubbing with protection recommended by your vet. Promptly report new pain, cloudiness or vision changes even after treatment has begun. Also monitor eating and general condition. In herpesvirus relapses, the aim is to reduce episode severity and frequency; permanent elimination of every symptom cannot be promised.
Prognosis
Many cats' symptoms can be controlled when the cause is identified and treatment is successfully given. A retained foreign body or uncorrected eyelid friction can sustain inflammation despite medication. Herpesvirus carriers may have later episodes, whereas treatment of a confirmed bacterial infection can aim to eliminate it.
Prevention
- Vaccinate against important respiratory infections, including FHV-1, FCV and chlamydia according to risk.
- Isolate sick animals.
- Maintain regular eye hygiene if your cat is prone to discharge.
- Reduce allergen contact.
- Support immunity through good-quality food and low stress.
Chlamydia vaccination is assessed according to infection risk and is not automatically needed for every cat. Separating a sick animal and washing hands reduce transfer of secretions. Calm, predictable conditions may help reduce herpesvirus relapses. As well as vaccination and environmental care, eye symptoms need treatment directed at their cause.
Important for cat owners
Chronic conjunctivitis is more than a cosmetic problem: it signals a serious disorder in the body or eyes. Remember that persistent eye inflammation needs professional examination, otherwise a cat can lose vision. Prompt assessment by a vet experienced in eye disease helps identify the cause and choose appropriate treatment.
This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.
Frequently asked questions
Can I wait a couple of weeks before examination?
Not if the eye is painful, cloudy or held closed. The threshold for chronic disease describes duration, not a safe waiting period. Milder recurring redness and discharge also need investigation of the cause.
Does a positive herpesvirus PCR give a definite diagnosis?
Not alone. Virus can be shed without explaining every current eye change. Your vet interprets the result alongside the eye examination and other findings.
Can I use drops left from a previous infection?
Do not start them without veterinary instructions. The new symptom's cause and corneal condition may differ. Corticosteroid-containing products can particularly be harmful with a surface ulcer or herpesvirus-related damage.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Conjunctivitis, Cornell Feline Health Centre, accessed 2026-11-05.
- Disorders of the Conjunctiva in Cats, Merck Veterinary Manual, accessed 2026-11-05.
- GUIDELINE for Feline Herpesvirus infection, European Advisory Board on Cat Diseases, accessed 2026-11-05.
- GUIDELINE for Chlamydia felis, European Advisory Board on Cat Diseases, accessed 2026-11-05.
- Feline Herpesvirus: Therapeutic Review, MSPCA-Angell, accessed 2026-11-05.
- Corneal Ulcers in Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Applying Eye Drops to Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Eosinophilic Keratoconjunctivitis in Cats, Veterinary Clinics of North America: Small Animal Practice / PubMed, accessed 2026-11-05.
- Conjunctivitis in Cats, VCA Animal Hospitals, accessed 2026-11-05.