Why Is My Cat’s Eye Red and Swollen? — Causes of Conjunctivitis and When to Visit the Vet

Eye HealthQ&AMeongsiljang Veterinary Advisory Board

Feline conjunctivitis typically presents with excessive tearing and redness of the eyes, most commonly caused by viral or bacterial infections. With early diagnosis and appropriate treatment, the condition is usually fully curable.

What Is Feline Conjunctivitis?

A close-up photo of a cat's eye with inflamed conjunctiva.

Feline conjunctivitis is a condition in which the conjunctiva—the thin membrane lining the eyelids and covering the white of the eye—becomes inflamed, leading to redness, excessive tearing, and discharge. - Main causes of conjunctivitis: In cats, infectious causes are common. Feline herpesvirus-1 (FHV-1) is the most frequent culprit, but *Chlamydia felis*, *Mycoplasma*, and feline calicivirus can also be responsible. Non-infectious triggers such as irritants or allergies may also play a role. - The importance of early diagnosis: It is best to seek veterinary care as soon as symptoms appear. Left untreated, conjunctivitis can lead to complications such as keratitis or corneal ulcers. - Key to treatment: Effective management requires targeted medication based on the underlying cause, along with consistent home care. - Prognosis: Healthy cats typically recover over the course of several weeks. However, FHV-1 remains latent in the body and cannot be completely eradicated. Even after symptoms subside, it is essential to complete the full course of medication as directed by your veterinarian.

What Are the Main Causes of Conjunctivitis?

The most common cause of feline conjunctivitis is feline herpesvirus-1 (FHV-1). - FHV-1 infection: This is the leading cause of infectious conjunctivitis in cats. The virus can reactivate (recur) during periods of stress, and cats with prior exposure may experience recurring symptoms. - Chlamydia felis: Another frequent cause of infectious conjunctivitis, treatable with antibiotics such as doxycycline. Respiratory symptoms associated with this infection are typically mild. - Other causes: Mycoplasma, calicivirus, and Bordetella can also be responsible. - Transmission: The infection can spread to other cats through contact with infected individuals. - Prevention tips: Managing stress and maintaining good hygiene are helpful preventive measures.

A scientific explanation of the viral and bacterial causes of feline conjunctivitis

What Are the Main Signs of Conjunctivitis?

The most common signs of feline conjunctivitis are redness and excessive tearing in the eyes. - Changes in discharge: Mucous discharge may appear white, yellow, or green. - Behavioral changes: The cat may blink frequently or rub its eyes more often. - Pain response: The cat may react painfully when the eyes are touched or keep them closed for extended periods. - Eyelid swelling: The eyelids may become swollen or difficult to open. - Early intervention is essential: If symptoms appear, consult a veterinarian promptly. Early treatment significantly aids recovery.

A photo of a cat with excessive tearing and discharge

Signs That Require Immediate Veterinary Care

If your pet has trouble keeping their eyes open (squinting or holding them shut), develops white spots on the eye, or reacts with pain when the eye is touched, these could be signs of keratitis or a corneal ulcer. In such cases, seek veterinary care as soon as possible. Even with early treatment, if there is no improvement within 5 to 7 days or if symptoms worsen or progress, specialized ophthalmic evaluation is necessary.

Comparison of Symptoms and Treatment by Conjunctivitis Type

Item	Main Cause	Main Symptoms	Treatment
Viral conjunctivitis	Feline herpesvirus-1	Excessive tearing, redness, eye closing	Antivirals (e.g., trifluridine), eye drops, supportive care
Bacterial conjunctivitis	Chlamydia felis, Mycoplasma	Yellow discharge, eyelid swelling	Antibiotics such as doxycycline, taken for about 3 weeks even after symptoms improve
Other infectious conjunctivitis	Calicivirus, Bordetella	Accompanied by respiratory symptoms, (with calicivirus) mouth ulcers	Antibiotics or supportive treatment tailored to symptoms

It varies by cause, but you need to continue the medication for a certain period even after symptoms improve to prevent recurrence. For chlamydial infection, doxycycline should be taken for about 3 more weeks (about 28 days total) even after symptoms improve, and for viral cases, antiviral medication is usually recommended for about 1 week after symptoms resolve.

How Is Conjunctivitis Treated?

Treatment for conjunctivitis varies depending on the underlying cause. - Viral cases: Antiviral medications and eye drops are used, and immune-supporting supplements can be helpful. - Bacterial cases: Antibiotics such as doxycycline must be administered consistently for at least three weeks. - Adherence to treatment duration: Stopping medication prematurely, even if symptoms have resolved, can lead to recurrence. - Regular check-ups are essential: Follow your veterinarian’s instructions and attend scheduled follow-up visits. - Tips for administering medication: Give medication in a calm environment to minimize stress for your cat. - Keys to successful treatment: Consistent care and accurate medication administration are crucial.

A veterinarian administering eye drops to a cat

Home Care Methods

Gently wipe the area around your cat’s eyes with gauze moistened with warm water. - Regular cleaning: When tears dry, they can harden around the eyes and increase the risk of infection. - Nail care: Trim your cat’s nails to prevent eye scratches, and check them daily. - Environmental adjustments: Maintain a quiet, stable environment to minimize stress. - Diet and hydration: Provide adequate food and water to support immune function. - Medication assistance: When administering medication, approach gently while considering your cat’s mood. - Observation habits: Check your cat’s eyes daily and visit the vet immediately if you notice any changes.

Precautions: Risk of Transmission to Humans and Hygiene Management

The most common causes of feline conjunctivitis are highly contagious among cats and can easily spread to other cats through contact with an infected animal. Although transmission to humans is rare, it cannot be entirely ruled out, so it is important to wash your hands thoroughly after handling an infected cat. Disinfect and separately manage items such as towels, bowls, and carriers used by the cat, and isolate the infected cat from other cats.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Conjunctivitis keeps coming back. Why is that?

Feline herpesvirus-1 can remain latent in the body for extended periods. It may reactivate during times of stress or when the immune system is compromised, potentially causing conjunctivitis to reappear.

The medication improves the eye condition, but how long should it be continued?

Even after symptoms disappear, it’s important to continue the medication for the duration prescribed by your veterinarian. The length of treatment varies depending on the cause. For viral infections, treatment typically continues for about a week after symptoms resolve, while bacterial infections like chlamydia often require an additional three weeks of medication even after improvement. Stopping treatment too early can lead to relapse or chronic conditions.

I have multiple cats in my home. Can they get infected?

Yes, conjunctivitis can easily spread among cats. Infected cats should be isolated separately, and contact with other cats should be minimized.

Can conjunctivitis be prevented with a vaccine?

The feline herpesvirus-1 vaccine helps reduce the severity of clinical disease, but it does not completely prevent infection. In other words, while complete prevention is difficult, the vaccine can help lessen the severity of symptoms.

Can’t I just administer eye drops at home?

Medications prescribed by a veterinarian are safe to use, but you should never administer medication on your own judgment. Incorrect medication can cause further damage to the eyes.

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References

[1] Clinical Medicine of the Dog and Cat, 4th Ed

[2] Clinical Atlas of Canine and Feline Ophthalmic Disease, 2nd Ed

[3] 100 Top Consultations in Small Animal General Practice