What Is Cat Conjunctivitis?
Conjunctivitis — commonly called “pink eye” — is inflammation of the conjunctiva, the thin transparent membrane that lines the inner surface of the eyelids and the white of the eye. In cats, conjunctivitis is one of the most common eye conditions seen in veterinary practice, and it’s particularly prevalent in kittens and multi-cat households.
The condition can affect one eye (unilateral) or both eyes (bilateral). Unilateral conjunctivitis is more often associated with a foreign body, injury, or localized infection. Bilateral conjunctivitis is more commonly caused by systemic infection — especially feline herpesvirus type 1 (FHV-1) or Chlamydophila felis.
While conjunctivitis is often uncomfortable rather than immediately dangerous, untreated or repeatedly recurring cases can lead to corneal scarring, chronic dry eye, or permanent eye damage — so prompt attention and appropriate treatment are important.
Symptoms of Cat Conjunctivitis
The hallmark signs include:
- Eye discharge: May range from clear and watery to thick, yellow-green, and mucoid. Discharge that crusts the eyelids shut overnight is common.
- Red or pink eye tissue: The conjunctiva (the pink tissue around the eye) becomes visibly red, swollen, and sometimes chemotic (puffy and water-filled).
- Squinting or blinking: The cat squints the affected eye partially or fully closed (blepharospasm), indicating photosensitivity or pain.
- Pawing at the eye: The cat rubs the affected eye with a paw or against surfaces, which risks worsening any corneal involvement.
- Third eyelid protrusion: The nictitating membrane (third eyelid) may be visible at the inner corner of the eye, a common response to ocular inflammation or illness.
- Sensitivity to light: The cat may avoid bright areas or keep the eye partially closed.
Additional symptoms like sneezing, nasal discharge, or fever suggest an underlying upper respiratory infection causing the conjunctivitis.
Common Causes of Conjunctivitis in Cats
Feline herpesvirus type 1 (FHV-1): This is the single most common cause of feline conjunctivitis and upper respiratory infection. Most cats are exposed to FHV-1 early in life, and it establishes a latent (dormant) infection that can reactivate during times of stress, illness, or immunosuppression — much like human cold sores. Reactivation causes episodes of eye discharge, squinting, and sometimes corneal ulceration (dendritic ulcers). There is no cure; management focuses on controlling flare-ups.
Chlamydophila felis: A bacterial pathogen causing persistent conjunctivitis, often with minimal respiratory signs. Vaccination against Chlamydophila is available and recommended in multi-cat environments. It responds well to antibiotics (doxycycline or chloramphenicol eye drops).
Mycoplasma felis: Another bacterial cause, often co-infecting cats alongside FHV-1 or Chlamydophila. Treatable with appropriate antibiotics.
Feline calicivirus: Can cause conjunctivitis alongside oral ulcers, sneezing, and fever. Less commonly associated with ocular disease than FHV-1.
Allergies: Environmental allergens (pollen, dust, mold) can trigger mild conjunctivitis in cats. This tends to be seasonal, affects both eyes equally, and may be accompanied by other allergy signs like sneezing or skin itching.
Foreign bodies: A grass seed, dust particle, or eyelash can cause sudden unilateral conjunctivitis with intense squinting. A vet needs to flush and examine the eye to identify and remove the offending item.
Eyelid abnormalities: Entropion (inward rolling of the eyelid, more common in flat-faced breeds like Persians) causes the eyelashes or skin to rub against the eye surface, triggering chronic conjunctivitis and corneal damage.
Diagnosing and Treating Cat Conjunctivitis
Your vet will examine the eye using an ophthalmoscope and may perform:
- Fluorescein stain: An orange dye applied to the eye that highlights corneal ulcers under blue light — essential to check for FHV-1-related ulceration before prescribing steroids.
- Schirmer tear test: Measures tear production to rule out dry eye (keratoconjunctivitis sicca) as a cause.
- PCR testing: Swabs of the eye can test for FHV-1, Chlamydophila, and Mycoplasma DNA.
Treatment depends on the cause:
- FHV-1: Antiviral medications (topical idoxuridine or cidofovir drops; oral famciclovir) reduce viral replication. L-lysine supplementation has been used to suppress viral activity, though evidence is mixed. Keeping stress low reduces reactivation frequency.
- Bacterial causes: Topical antibiotic eye drops or ointment (chloramphenicol, oxytetracycline, or fusidic acid) are first-line. Chlamydophila responds well to systemic doxycycline as well.
- Allergic conjunctivitis: Antihistamines, avoidance of the allergen, and occasionally topical anti-inflammatories.
- Important caution: Topical corticosteroid eye drops should never be used without ruling out corneal ulceration first — steroids significantly worsen FHV-1 corneal ulcers and can cause permanent eye damage.
Home Care and When to See a Vet
For mild discharge, gently wipe away crusted discharge with a damp, clean cotton pad — use a fresh pad for each eye to avoid spreading infection. Never use the same cloth on both eyes if conjunctivitis is unilateral.
See a vet promptly if: the eye is cloudy or bluish (possible corneal involvement), discharge is thick yellow-green, the cat is holding the eye fully shut, the condition worsens over 24 hours, or the cat shows signs of systemic illness (lethargy, not eating, fever).
Do not use human eye drops in cats — many contain preservatives or ingredients that are harmful to feline eyes. Only use medications specifically prescribed or recommended by your veterinarian.
The most common cause of cat conjunctivitis — feline herpesvirus (FHV-1) — is species-specific and cannot infect humans. Chlamydophila felis can very rarely cause mild conjunctivitis in immunocompromised people. Standard hygiene (washing hands after touching an affected cat’s face) is sufficient precaution for healthy adults.
No — do not use human eye drops in cats without veterinary guidance. Many human eye preparations contain preservatives, vasoconstrictors, or other ingredients that are toxic or harmful to cats. Use only products specifically prescribed or recommended for feline use by your vet.
Recurrent conjunctivitis is most commonly caused by feline herpesvirus (FHV-1), which establishes a latent infection that reactivates during stress, illness, or changes in the environment. Managing stress, maintaining good nutrition, and discussing antiviral options or L-lysine supplementation with your vet can help reduce recurrence frequency.
With appropriate treatment, most cases of bacterial conjunctivitis resolve within 1-3 weeks. Viral (FHV-1) flare-ups typically resolve in 2-4 weeks but may recur. Untreated conjunctivitis can persist or worsen, so veterinary treatment is always recommended.
Yes — conjunctivitis causes discomfort ranging from mild irritation to significant pain, especially when corneal ulcers are involved. Signs of pain include intense squinting, light sensitivity, pawing at the eye, and behavioral changes like hiding or reduced appetite. Pain management is an important part of treatment.