Feline Conjunctivitis

Overview

Conjunctivitis is inflammation of the pink membrane lining the eyelids and covering part of the eyeball. It's one of the most common eye problems in cats and has several possible causes, most notably feline herpesvirus, which is part of why a persistent or recurring case deserves proper veterinary diagnosis rather than repeated home treatment guessing.

Symptoms

• Eye redness (mild, common)
• Watery or thick discharge (mild, common)
• Squinting (moderate, common)
• Third eyelid visible (moderate, uncommon)

Causes

Most commonly feline herpesvirus-1 infection (especially in cats with a history of upper respiratory infection), also chlamydia (Chlamydophila felis), other bacteria, allergies, or irritants (dust, smoke, foreign material). Feline herpesvirus (FHV-1) is the single most common cause, often the same virus responsible for upper respiratory infections, capable of remaining dormant in a cat's system long-term and flare up periodically, particularly during stress; Chlamydia felis and Mycoplasma are other significant infectious causes, while allergies, irritants (dust, smoke, cleaning product fumes), and foreign material in the eye account for a meaningful share of non-infectious cases.

Risk Factors

Young kittens, cats with a history of upper respiratory infection, multi-cat households/shelters, and cats with any latent herpesvirus infection (very common in the general cat population, often reactivating during stress).

Transmission

Direct contact with ocular/nasal discharge from an infected cat, shared bowls/bedding, and sneezing; herpesvirus can also reactivate from a cat's own latent infection during stress without new exposure.

Incubation Period

Typically 2-5 days for infectious causes.

Disease Stages & Progression

Ranges from mild redness and watery discharge to more significant swelling, thick discharge, and, in herpesvirus cases, potential corneal involvement if untreated.

Early Warning Signs

Redness of the pink tissue around the eye, watery discharge, mild squinting, or excessive blinking.

Advanced Symptoms

Thick yellow-green discharge, significant swelling, the third eyelid becoming more visible, pronounced squinting or eye-closing, and in some herpesvirus cases, corneal ulceration.

Diagnostic Methods

Physical exam of the eye, fluorescein stain to rule out a corneal ulcer, and PCR/swab testing for a specific cause in persistent, recurrent, or unusually severe cases. Diagnosis usually starts with direct examination, but identifying the specific underlying cause — particularly distinguishing herpesvirus from Chlamydia or Mycoplasma, which can look clinically similar but need different treatment — sometimes requires a specific swab test (PCR testing) of eye discharge, particularly for chronic or recurring cases rather than a single isolated episode.

Veterinary Examination Process

Close examination of both eyes (even if only one looks affected), checking for corneal involvement, and assessing for concurrent upper respiratory signs (sneezing, nasal discharge) that often accompany herpesvirus-related conjunctivitis.

Recommended Lab Tests

PCR swab testing for herpesvirus/chlamydia in recurrent or treatment-resistant cases.

Diagnostic Imaging

Not applicable; a fluorescein stain test (not imaging in the traditional sense but a simple in-clinic dye test) is used to check for a corneal ulcer if suspected.

Blood Test Indicators

Not typically used for straightforward conjunctivitis; PCR testing of an eye swab can identify a specific infectious cause (herpesvirus, chlamydia) in recurrent or non-responsive cases.

Biopsy / Histopathology

Not applicable for typical conjunctivitis.

Differential Diagnoses

Corneal ulcer, uveitis, glaucoma, foreign body in the eye, and allergic conjunctivitis — the fluorescein stain and a full eye exam help distinguish these serious look-alikes from straightforward conjunctivitis.

Home Monitoring Guidance

Gently wiping away discharge with a clean, damp cloth, and watching closely for any sign of the eye itself (not just the surrounding tissue) becoming cloudy or more painful.

Veterinary Treatment Options

Depends on cause: supportive care (keeping the eye clean) for mild viral cases, topical or oral antiviral medication for confirmed herpesvirus, antibiotic eye drops/ointment for bacterial or chlamydial causes, and addressing any underlying allergy/irritant if that's the driver. Treatment depends on the underlying cause: bacterial causes (Chlamydia, Mycoplasma) respond to topical or oral antibiotics, herpesvirus-associated conjunctivitis may be treated with antiviral medication (particularly for severe or recurrent cases) alongside supportive care like keeping the eye area clean, and allergy-related conjunctivitis benefits from identifying and reducing the specific trigger alongside anti-inflammatory treatment as needed.

Surgery Requirements

Not applicable for typical conjunctivitis; a corneal ulcer that doesn't respond to medical treatment could require a surgical procedure in more severe/complicated cases.

Recovery Timeline

Mild cases often improve within a week with appropriate treatment; herpesvirus-related conjunctivitis can recur intermittently throughout a cat's life during periods of stress, since the virus isn't cleared from the body once infected.

Possible Complications

Corneal ulceration, chronic or recurring conjunctivitis, and in severe untreated cases, permanent eye damage. Untreated or severe conjunctivitis, particularly from herpesvirus, can progress to corneal ulceration (a genuinely more serious, painful condition affecting the eye's surface directly) or, in chronic cases, cause enough scarring to affect vision — prompt treatment of ongoing or worsening conjunctivitis specifically helps avoid this progression.

Long-Term Management

For cats with recurrent herpesvirus-related conjunctivitis, reducing stress where possible and having a treatment plan ready with your vet for flare-ups.

Prevention

Vaccination against feline herpesvirus and calicivirus (part of the core FVRCP vaccine) reduces severity though doesn't fully prevent infection or later reactivation; good hygiene in multi-cat environments reduces spread. Core vaccination (which includes protection against herpesvirus and calicivirus, two major contributors to upper-respiratory-and-eye infections) reduces both the likelihood and severity of viral conjunctivitis; managing stress in cats with known recurrent herpesvirus flare-ups can help reduce how often the dormant virus reactivates, since stress is a well-documented trigger for herpesvirus recurrence specifically.

Vaccination Availability

The FVRCP core vaccine includes protection that reduces the severity of herpesvirus-related disease, though it doesn't guarantee complete prevention.

Prognosis

Very good for most cases with appropriate treatment; herpesvirus-associated cases tend to recur intermittently but are generally manageable long-term.

References

American College of Veterinary Ophthalmologists; International Cat Care eye health resources.

Medications Used

• Topical antibiotic eye ointment/drops for bacterial causes
• Topical or oral antiviral medication (e.g., famciclovir) for confirmed or strongly suspected herpesvirus
• L-lysine supplementation is sometimes used for herpesvirus management, though evidence for its effectiveness is mixed and it should be viewed as a supportive measure discussed with your vet, not a proven core treatment

Estimated Treatment Cost by Country

Frequently Asked Questions