Moderate severity

Dry Eye (Keratoconjunctivitis Sicca)

A shortage of the watery part of the tear film that leaves the surface of the eye dry, sore and prone to infection, thick mucus discharge and, over time, damage to the cornea.

⚠️ Common symptoms

Thick, sticky, yellow-green mucus discharge that keeps returningA dull, dry or lacklustre look to the surface of the eyeRedness and squinting, and rubbing or pawing at the eyeRecurring or stubborn conjunctivitis that never quite clearsCloudiness, pigment or blood vessels creeping across the cornea in long-standing cases

Keratoconjunctivitis sicca, usually shortened to KCS or simply "dry eye", means inflammation of the cornea and conjunctiva caused by a lack of tears. The tear film is not just water — it is a carefully balanced layer that lubricates the eye, washes away debris, feeds the surface of the cornea and carries infection-fighting substances. When the watery part of that film runs short, the surface of the eye dries out, and the result is a red, sore, sticky eye that never seems to fully recover.

One of the tell-tale signs is a thick, ropey, yellow-green mucus discharge. With less watery tear to dilute it, the mucus part of the film becomes concentrated and clingy, and owners often find themselves wiping the same gluey discharge away day after day. The eye may look dull rather than glossy, the cat squints and rubs, and what looks like ordinary conjunctivitis simply refuses to clear up with standard treatment.

In cats, dry eye is less common than in dogs and has a different flavour: the biggest single cause is scarring from feline herpesvirus, the same virus behind so many feline eye and respiratory problems. By damaging the tear glands and the conjunctiva, a bad or repeated herpes infection can leave the eye unable to keep itself wet. Immune-mediated inflammation, nerve damage and certain medications can also be to blame.

Diagnosis is straightforward for a vet: a simple, painless strip test (the Schirmer tear test) measures how much tear the eye produces in a minute, and a low reading confirms the problem. The eye surface is then checked for ulcers or scarring. Treatment is usually lifelong — tear-stimulating ointments such as ciclosporin to coax the glands back into action, plus artificial tears and antibiotics as needed — and with consistent daily care most cats stay comfortable and keep their sight. The key for owners is not to treat a gluey, recurring eye as a trivial nuisance: catching a tear deficiency early, before the cornea is scarred, makes all the difference.

🔍 Causes

Dry eye happens when the glands that make the watery layer of tears under-produce. In cats a leading cause is damage from feline herpesvirus infection, which can scar the tear glands and the conjunctiva. Other triggers include immune-mediated inflammation of the tear glands, certain drugs, damage to the nerve supply of the eye, and general anaesthesia in susceptible cats. It is less common in cats than in dogs, which can mean it is missed until the eye is badly affected.

🛡 Prevention

Dry eye cannot always be prevented, but keeping cats up to date on core vaccination reduces severe herpesvirus flare-ups that can scar the tear glands. Having any persistent eye discharge, redness or squinting checked promptly means a tear deficiency is caught before the cornea is damaged. For a cat already diagnosed, the single most important thing is giving the prescribed drops exactly as directed, every day, for life.

💊 Treatment

The mainstay of treatment is lifelong tear-replacement and, where appropriate, medication that stimulates natural tear production, such as topical ciclosporin or tacrolimus prescribed by a vet. Artificial-tear drops or gels keep the surface lubricated between doses, and antibiotic drops clear any secondary infection. Gently wiping away the mucus keeps the eye comfortable. Because most cases need treatment for life, regular rechecks let the vet measure tear production and adjust the drops. Underlying causes, such as feline herpesvirus, are treated alongside.

When to see a vet: See a vet for any eye that produces thick, recurring mucus discharge, looks red or sore, or is being rubbed, and for any conjunctivitis that keeps coming back despite treatment. Dry eye is progressive and can permanently scar the cornea and threaten sight if left untreated, so a sore, gunky eye is always worth a proper examination rather than repeated courses of the same drops.

⚕️ Medical disclaimer

  • This information is educational only and is not a substitute for veterinary advice.
  • Symptoms overlap between conditions — only a vet can diagnose accurately.
  • Never withhold treatment or self-medicate based on information found online.
  • When in doubt, call your vet. Early intervention almost always leads to better outcomes.

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