CONDITION
Keratoconjunctivitis Sicca (Dry Eye)
Keratoconjunctivitis sicca describes what happens when the tear glands produce too little of the watery layer that normally keeps the eye moist. Without enough tears, the surface of the eye becomes dry and inflamed, and the body often compensates with a thick, sticky discharge that can look quite different from healthy tearing. In many dogs the condition develops gradually over months. It can also begin suddenly, for example during treatment with certain sulphonamide medicines, and in that situation a corneal ulcer can be present from the start. Owners often notice a change in the appearance of the eye itself: a dull or cloudy look to the surface, discharge that is yellow or green rather than clear, redness, squinting, or a sense that the eye looks uncomfortable. Some arrive wondering about recurring 'eye infections' that never quite clear, or about one eye that looks different from the other. The signs can wax and wane early on, which sometimes delays recognition. This page explores what dry eye can look like in its different stages, what drives the loss of tear production, how the diagnosis is made, and the range of approaches used to manage it over time. The aim is to help you understand what may be happening and what shape that management might take.
Why this matters now
The immune-mediated form usually develops gradually and is most often diagnosed in middle-aged dogs, and the risk rises with age. Some breeds can be affected much younger. In one UK referral study, Cavalier King Charles Spaniels showed one peak of cases before two years of age, and their dry eye tended to start more suddenly and with more ulcers. Certain breeds, including West Highland White Terriers, Cocker Spaniels, Cavalier King Charles Spaniels, and English Bulldogs, appear to have a higher predisposition. Owners may initially dismiss early signs as minor eye irritation, but the condition often progresses if underlying factors are not addressed. Dry eye caused by sulphonamide antibiotics, such as trimethoprim-sulphonamide, can begin within days of starting the course, or only after several weeks or months. In some dogs tear production returns after the drug is stopped, and in others the loss is permanent.
Without adequate tear production, the surface of the eye can become chronically inflamed. Early on, the eye might appear slightly dull or have a thick discharge. Over months, pigmentation and blood vessel growth across the cornea can occur and can gradually reduce vision. Corneal ulceration runs on a much shorter timescale. An ulcer can form at any stage, and on a dry eye it is more likely to become infected. An infected ulcer can soften and dissolve the cornea in as little as 12 to 24 hours, and perforation of the eye, which can end in loss of sight in that eye, is one possible outcome. Brachycephalic breeds such as the Shih Tzu, Pug and English Bulldog carry extra risk, partly because their eyelids often do not fully close over the eye. The condition tends to be lifelong in most cases, though many dogs respond well to ongoing management.
Signals & patterns
Early signals
Thick, mucoid eye discharge
A sticky, stringy discharge that accumulates around the eye, often more noticeable than normal tear residue.
Eye redness or irritation
The white of the eye and conjunctiva may appear pink or inflamed, suggesting ongoing surface irritation.
Frequent blinking or squinting
Dogs may blink more often or hold the eye partly closed. Mild squinting can come from dryness alone. Squinting that increases suddenly, or an eye held fully shut, is also how a corneal ulcer typically shows, and the two cannot be told apart without a fluorescein stain.
Dull or lacklustre eye surface
The cornea may lose its normal shine and appear slightly hazy or less reflective than usual.
Corneal ulceration, at any stage
An ulcer can develop at any stage of dry eye and is sometimes the first problem noticed. Many ulcers cannot be seen without a fluorescein stain. Changes that can go with one include a sudden increase in squinting or rubbing at the eye, an eye held shut, a new cloudy, grey or bluish patch on the cornea, or a visible dent in its surface. On a dry eye an ulcer is more prone to infection, and an infected ulcer can soften and dissolve through the cornea in as little as 12 to 24 hours.
Later signals
Corneal pigmentation
Brown or black pigment may spread across the surface of the eye as a chronic protective response.
Visible blood vessels on cornea
New blood vessels may grow across the normally clear cornea, a process called neovascularisation.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosing keratoconjunctivitis sicca typically involves assessing tear production alongside examination of the eye surface. A thorough ophthalmic examination helps identify secondary changes that may have developed.
Schirmer tear test
Fluorescein staining
Slit lamp examination
Tonometry
Options & trade-offs
Management of keratoconjunctivitis sicca typically focuses on stimulating natural tear production, supplementing moisture, and controlling inflammation. The approach may be adjusted based on response and the presence of any secondary complications.
Immunomodulatory eye ointment or drops
Ciclosporin eye ointment is authorised in the UK for dogs with dry eye and can help restore tear production by reducing immune-mediated destruction of the tear glands. Tacrolimus has no UK veterinary authorisation. It is specially prepared as drops or ointment and prescribed under the veterinary cascade, usually when ciclosporin has not produced enough response.
Trade-offs: May take several weeks to show full effect. Lifelong treatment is typically needed. Some dogs may develop local irritation initially.
Artificial tear supplements
Lubricating drops or gels provide moisture to protect the surface of the eye when natural tears fall short.
Trade-offs: May require frequent application throughout the day. Can be used alongside other treatments. Some formulations last longer than others.
Anti-inflammatory medications
Topical anti-inflammatory drugs may help reduce corneal inflammation and associated discomfort.
Trade-offs: Usually used short-term or intermittently. Topical steroids can stop a corneal ulcer healing and make it worse, including softening of the cornea, so they are typically used only once a fluorescein stain has shown no ulcer.
Surgical options
In cases that do not respond adequately to medical management, procedures like parotid duct transposition can redirect saliva to moisten the eye.
Trade-offs: Reserved for refractory cases. Can be effective but requires surgical expertise and may have complications including mineral deposits on the eye.
Common misconceptions
"Dry eye will resolve once the discharge clears up"
The underlying deficiency in tear production typically persists even when symptoms appear improved. Ongoing management is usually necessary to maintain eye health.
"Eye discharge means there is an infection"
The thick discharge in KCS results from mucus overproduction due to inadequate tears, not necessarily infection. However, secondary bacterial involvement can occur.
"This condition only affects older dogs"
Most cases are diagnosed in middle age and the risk keeps rising into old age, but KCS can develop at various ages, particularly in predisposed breeds. Younger dogs are not immune.
Related conditions
Conjunctivitis
Conjunctivitis and keratoconjunctivitis sicca can sometimes be confused early on, as both cause redness, discharge, and discomfort. The appearance of the discharge does not reliably separate them. A Schirmer tear test, which measures tear production, shows whether a lack of tears lies behind the redness and discharge.
Corneal Ulcers
Corneal ulcers can develop as a consequence of keratoconjunctivitis sicca, because the dry surface of the eye is more vulnerable to injury and slower to heal. An ulcer on a dry eye is also more prone to infection and to softening, which can progress to perforation. In some cases, recurring ulcers may be the first sign that tear production has fallen below what the eye needs.
The page on this condition is being checked again and is offline for now.
Distichiasis
Distichiasis, where extra eyelashes grow from the eyelid margin and rub on the eye, typically causes excess tearing rather than a lack of tears. Both conditions can cause squinting, redness, discharge and corneal ulcers, and breeds such as the Cocker Spaniel, Cavalier King Charles Spaniel, Shih Tzu and Bulldog are predisposed to both, so a tear test and close examination of the eyelid margins help separate them.
Immune-Mediated Polyarthritis
Immune-mediated polyarthritis and keratoconjunctivitis sicca can both arise from immune system dysfunction, and in some cases they occur together as part of a broader autoimmune process. The pattern of immune activity that damages tear glands may also target joint tissues in certain individuals.
Pannus (Chronic Superficial Keratitis)
Pannus and keratoconjunctivitis sicca are both immune-mediated conditions affecting the eye, and while pannus starts in the cornea itself and dry eye starts in the tear glands, they can occasionally occur in the same animal. Each condition produces a characteristic change in the appearance of the eye, and distinguishing between them often requires close examination and sometimes testing.
Cherry Eye
The gland of the third eyelid produces part of the tear film. When a prolapsed gland is removed rather than repositioned, tear production can fall and dry eye can follow.
Facial Nerve Paralysis
The nerve fibres that stimulate the tear gland travel with the facial nerve, so disease affecting that nerve can reduce tear production on the same side, often with a dry nostril. An eye that cannot blink fully is also more exposed, which adds to the risk of corneal ulcers.
Dry eye tends to involve two timescales. Discharge, dullness and pigment change over weeks to months, and medication schedules and response to treatment are followed over that period. Corneal ulceration is faster. A sudden increase in squinting or rubbing, an eye held shut, a new cloudy, grey or bluish patch, a visible dent in the surface of the cornea, or a change in the eyes during or after treatment with a sulphonamide medicine can each reflect an ulcer or a sudden fall in tears. Whether an ulcer is present, and how deep it is, cannot be judged at home. It takes a fluorescein stain and a magnified examination, and an infected ulcer on a dry eye can progress to perforation in as little as 12 to 24 hours. Understanding that this condition often requires long-term attention can help with planning and expectations.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS