SYMPTOM
Eye redness
Owners may observe eye redness in their pet.
Various conditions
This symptom can occur in multiple conditions and warrants further assessment.
Conjunctivitis
Inflammation of the membrane lining the eyelids and covering the white of the eye is the most common cause of a red eye overall. In cats it is frequently linked to feline herpesvirus, while in dogs bacterial infection or allergy are more typical triggers. It usually produces diffuse redness with watery to mucoid discharge and only mild discomfort.
Corneal Disease
Damage to the clear surface of the eye — from ulceration, the dark corneal sequestrum seen in cats, eosinophilic keratitis in cats, or chronic superficial keratitis (pannus) in dogs — exposes sensitive corneal tissue and triggers a ring of blood vessel growth around the edge of the cornea. German Shepherds are predisposed to pannus, while flat-faced breeds and cats with herpesvirus are more prone to ulceration and sequestrum formation.
Uveitis and Intraocular Bleeding
Inflammation inside the eye, or bleeding into the front chamber (hyphaema) following trauma or a bleeding disorder, produces deep, diffuse redness with cloudiness and discomfort rather than the surface redness seen in conjunctivitis. In cats, systemic infections such as toxoplasmosis are a recognised trigger for uveitis.
Eyelid Conformation Abnormalities
Eyelids that roll inward or outward (entropion or ectropion), or eyelashes that grow in an abnormal direction (distichiasis), cause chronic low-grade mechanical irritation and redness through repeated rubbing on the eye surface. Breeds with loose facial skin or heavy lower lids, such as Basset Hounds, Bloodhounds, and Cocker Spaniels, are more commonly affected.
Environmental Irritation
Dust, pollen, grass seeds, or mild airborne irritants can cause transient redness and watering as the eye's normal protective response, without reflecting any underlying eye disease. This tends to affect one eye more than the other and settles once the irritant is removed or flushed away, representing one of the more benign explanations for an occasional red eye.
Why timing matters
Early observation
Early recognition allows prompt assessment and intervention if needed.
Later presentation
Persistent or worsening signs may indicate progression requiring attention.
The significance of this symptom depends on its context, duration, and associated findings.
Conditions commonly associated
Corneal Ulcers
Inflammation around the ulcer causes visible redness of the conjunctiva and sclera.
Uveitis
Redness of the eye is a hallmark sign of inflammation within the uveal tract.
Corneal Sequestrum in Cats
Irritation and inflammation around the corneal lesion commonly redden the surrounding eye tissue.
Distichiasis
Ongoing surface irritation from the misplaced lashes leaves the conjunctiva looking pink or inflamed.
Ectropion
Chronic exposure of the unprotected conjunctival surface leaves it persistently pink and inflamed.
Eosinophilic Keratitis in Cats
Eosinophilic infiltration of the cornea inflames the surrounding tissue, giving the eye a reddened appearance.
Hyphaema
Blood collecting in the front chamber gives the eye a reddish or pinkish tinge that is visible from the outside, sometimes as a distinct pooled layer.
Pannus (Chronic Superficial Keratitis)
The blood vessels that grow into the cornea as part of pannus can give the surrounding eye a reddened appearance.
Toxoplasmosis
Inflammation inside the eye caused by this parasite makes the affected eye appear red and uncomfortable.
When to explore further
When the symptom is persistent or worsening
When other signs are present alongside
When daily activities or quality of life are affected
When there is uncertainty about the cause
Noting when this symptom occurs, any triggers, and how it changes over time can provide useful information for veterinary discussions.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS