SYMPTOM
Eye discharge or watery eyes
Excessive tearing, watery discharge, or accumulation of mucoid or purulent material around the eyes, sometimes with reddened or swollen conjunctiva.
Upper Respiratory Infection
Eye discharge and conjunctivitis frequently accompany upper respiratory infections, particularly in cats. Feline herpesvirus-1 has a strong tropism for both respiratory and conjunctival epithelium, often producing concurrent nasal and ocular signs. Chlamydophila felis characteristically produces conjunctivitis that may begin unilaterally before becoming bilateral. The discharge may range from clear and serous in early stages to mucopurulent as secondary bacterial infection develops.
Conjunctivitis
Inflammation of the conjunctival membranes can produce ocular discharge ranging from clear and watery to thick and purulent, depending on the cause. Infectious, allergic, and irritant causes can all produce conjunctivitis. The conjunctiva may appear reddened and swollen, and the animal may show signs of ocular discomfort such as squinting, rubbing at the eyes, or increased blinking.
Keratoconjunctivitis Sicca (Dry Eye)
Inadequate tear production results in chronic ocular surface dryness that typically produces a thick, mucoid discharge. The eyes may appear dull and the cornea may develop a hazy or pigmented appearance over time. In dogs, keratoconjunctivitis sicca is often immune-mediated and may be associated with certain breeds or concurrent conditions.
Corneal Disease
Corneal ulcers, erosions, or foreign bodies can produce excessive tearing and ocular discharge as part of the eye's protective response. The discharge may be serous initially but can become mucopurulent if secondary infection develops. Corneal disease is often accompanied by squinting, light sensitivity, and visible cloudiness of the corneal surface.
Nasolacrimal Duct Obstruction
Blockage of the nasolacrimal duct — the drainage channel that normally carries tears from the eye to the nasal cavity — results in tear overflow (epiphora) that appears as excessive wetness or staining below the eye. The obstruction may be congenital, as in brachycephalic breeds, or acquired due to infection, inflammation, or trauma.
Allergic Eye Disease
Allergic reactions affecting the conjunctiva can produce watery, clear discharge alongside redness and itching. The discharge is typically bilateral and serous, and may follow seasonal patterns corresponding to environmental allergen exposure. The eyes may appear puffy or the conjunctiva may be visibly swollen.
Why timing matters
Early observation
Early eye discharge may present as mild watering, slight crusting in the corners of the eyes upon waking, or a barely noticeable increase in tear staining on the fur below the eyes. The eyes may appear slightly more moist than usual, and the animal may occasionally paw at or rub the affected eye. At this early stage, the discharge is often clear and serous, and the conjunctiva may show only subtle redness.
Later presentation
As the underlying process progresses, the discharge may increase in volume and change character from clear and watery to mucoid or mucopurulent. The periocular fur may become chronically stained, matted, and potentially excoriated from persistent moisture. The conjunctiva may become more prominently reddened and swollen, and the animal may show more persistent signs of ocular discomfort including squinting, reduced eye opening, and light sensitivity. In severe cases, secondary corneal changes may develop.
The trajectory of eye discharge depends on its cause. Viral conjunctivitis typically follows an acute course with resolution over one to three weeks, though herpesvirus-associated disease may recur. Bacterial conjunctivitis may respond to appropriate treatment but can become chronic if the underlying cause is not addressed. Keratoconjunctivitis sicca typically produces progressive changes that worsen without management. Allergic causes may fluctuate with allergen exposure. Nasolacrimal obstruction tends to produce consistent, ongoing epiphora that does not resolve spontaneously.
Conditions commonly associated
Chronic Upper Respiratory Disease in Cats
Ocular discharge and conjunctivitis frequently accompany chronic upper respiratory disease in cats due to feline herpesvirus tropism for both respiratory and conjunctival epithelium, often flaring alongside nasal signs during viral reactivation episodes.
Corneal Ulcers
Excessive tearing is one of the cornea's immediate responses to ulceration, as reflex tear production increases to flush the damaged surface and provide antimicrobial and growth factor support.
Glaucoma in Dogs
Excessive tearing may accompany glaucoma as a pain response to elevated intraocular pressure, particularly during acute pressure elevations.
Conjunctivitis
Excess tear production or mucoid/purulent discharge is a characteristic feature of conjunctival inflammation.
Keratoconjunctivitis Sicca (Dry Eye)
Keratoconjunctivitis sicca can cause thick, mucoid discharge as the eye overproduces mucus to compensate for inadequate tear production.
Entropion
Chronic irritation from entropion stimulates excessive tear production, often resulting in tear staining down the face.
Cherry Eye
Cherry eye often causes increased tearing initially, with potential for mucoid discharge as secondary inflammation develops.
Feline Herpesvirus (FHV-1)
Conjunctivitis and corneal involvement cause watery to mucoid discharge from affected eyes.
When to explore further
Eye discharge that persists for more than a few days, particularly if it changes from clear and watery to thick, coloured, or mucopurulent, may suggest an infectious or inflammatory process that is unlikely to resolve without intervention.
Unilateral eye discharge — affecting only one eye — may suggest a localised cause such as a corneal injury, foreign body, or nasolacrimal obstruction on the affected side, rather than a systemic or bilateral process.
Eye discharge accompanied by significant squinting, reluctance to open the eye, or visible changes to the corneal surface (cloudiness, colour change, or surface irregularity) may suggest corneal involvement that warrants prompt attention.
Chronic thick, mucoid discharge that does not respond to simple cleaning, particularly if accompanied by a dull or dry-appearing eye surface, may suggest inadequate tear production rather than overproduction of discharge.
Eye discharge that develops alongside nasal discharge, sneezing, or other respiratory signs may suggest an upper respiratory infection affecting both the ocular and respiratory systems simultaneously.
Noting whether the discharge affects one or both eyes, its character (clear, cloudy, thick, coloured), and whether it varies with time of day or environmental conditions can help characterise the underlying process. Observing whether the animal is squinting, rubbing at the eyes, or showing light sensitivity provides additional context about the degree of discomfort. Gently cleaning the discharge with a damp cotton pad and observing how quickly it reaccumulates can give a sense of the production rate and whether the process is ongoing.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS