CONDITION

Conjunctivitis

Why this matters now

Conjunctivitis can occur at any age and may develop suddenly or progress gradually. Seasonal patterns sometimes emerge, with pollen-related cases more common in spring and summer. Infectious causes may cluster in multi-animal households or after exposure to unfamiliar animals.

The condition may begin with mild watering or redness before progressing to more obvious discharge and discomfort. Without identification of the underlying cause, signs may persist, recur, or spread to the other eye. Some forms can progress to involve deeper eye structures if the initial inflammation is not addressed.

Signals & patterns

Early signals

Increased tear production or watery eyes

The eye may appear excessively wet or have clear discharge tracking down the face.

Mild redness around the eye margins

The conjunctival tissue may appear pink or slightly inflamed compared to normal.

Increased blinking frequency

Subtle discomfort may cause more frequent blinking or squinting, particularly in bright light.

Pawing at the eye or face

Animals may rub at the affected eye with a paw or against furniture.

Later signals

Thick, coloured discharge

Discharge may become yellow, green, or white and accumulate around the eye, suggesting possible bacterial involvement.

Marked swelling of the eyelids

Significant inflammation may cause visible puffiness around the eye.

Holding the eye partially or fully closed

Persistent discomfort or light sensitivity may lead to obvious squinting or inability to open the eye fully.

Click to read about the biological mechanisms

How this is usually investigated

Evaluation of conjunctivitis aims to identify the underlying cause and assess whether deeper eye structures are affected. Various examinations and tests may provide diagnostic clarity.

Ophthalmic examination

Purpose: To assess the extent of inflammation and check for involvement of other eye structures
Considerations: Includes examination of the cornea, anterior chamber, and eyelid structures. A slit lamp may provide detailed views.

Fluorescein staining

Purpose: To detect corneal ulceration that may accompany or complicate conjunctivitis
Considerations: Uptake of green dye indicates epithelial damage. Essential to identify before certain treatments are used.

Schirmer tear test

Purpose: To measure tear production and identify dry eye as an underlying cause
Considerations: Low readings may indicate keratoconjunctivitis sicca, which requires specific management.

Bacterial or viral culture/PCR

Purpose: To identify specific infectious agents when infection is suspected
Considerations: May be particularly useful in cats where feline herpesvirus is common, or when initial treatment has not resolved signs.

Cytology or conjunctival swab

Purpose: To examine cell types present and identify potential causes
Considerations: Can help distinguish allergic, bacterial, and viral aetiologies based on predominant cell populations.

Options & trade-offs

Management depends on identifying and addressing the underlying cause. Various approaches may be appropriate depending on the specific diagnosis.

Topical anti-inflammatory preparations

Eye drops or ointments aimed at reducing inflammation and discomfort.

Trade-offs: Some preparations are contraindicated if corneal ulceration is present. Different formulations suit different causes of inflammation.

Antimicrobial therapy

Antibacterial or antiviral medications applied topically or given systemically.

Trade-offs: Appropriate when infection is confirmed or strongly suspected. Some require frequent application, which may be challenging for some pets and owners.

Artificial tears and lubrication

Lubricating preparations to support tear film and comfort.

Trade-offs: Helpful as supportive care and essential in dry eye. May need frequent application throughout the day.

Addressing underlying causes

Management of allergies, eyelid abnormalities, or other contributing factors.

Trade-offs: Long-term management may be needed for allergic or conformational causes. Some conditions may warrant surgical correction.

Common misconceptions

Misconception:

"Conjunctivitis is always contagious"

Reality:

While infectious conjunctivitis can spread between animals, many cases result from allergies, dry eye, or conformational issues and are not transmissible.

Misconception:

"Red eyes will resolve on their own"

Reality:

Some mild cases may improve spontaneously, but persistent or worsening signs often indicate a need for veterinary assessment to prevent complications.

Misconception:

"Human eye drops are safe for pets"

Reality:

Many human preparations contain ingredients that are inappropriate or harmful for animals. Veterinary-specific products are formulated for the unique needs of different species.

Noting when symptoms first appeared and whether one or both eyes are affected can help guide discussions with a veterinary professional. Observing the character of any discharge, response to bright light, and whether the pet can open the eye fully provides useful information. Identifying any potential triggers such as recent exposure to other animals, new environments, or seasonal patterns may also be relevant.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS