Keratoconjunctivitis sicca (KCS), commonly known as dog dry eye, is a chronic eye condition where the tear glands produce insufficient tears to keep the eye surface properly lubricated. Without adequate tear film, the cornea and conjunctiva become irritated, inflamed, and over time, permanently damaged. KCS is one of the most common eye diseases in dogs — and one of the most treatable, when caught early.
What Is KCS (Dry Eye) in Dogs?
The tear film covering a dog’s eye has three layers: an outer oily layer that prevents evaporation, a middle watery layer that provides moisture and delivers oxygen and nutrients, and an inner mucous layer that helps the film adhere to the cornea. In KCS, the middle watery layer is deficient — produced either in too small a quantity or not at all.
Without this lubrication, the cornea is exposed to friction with every blink, leading to chronic irritation, secondary bacterial infections, and eventually corneal ulceration and scarring. Untreated KCS causes progressive vision impairment and, in severe cases, blindness.
KCS is diagnosed using a Schirmer Tear Test (STT), which measures tear production in millimeters per minute. Normal is 15 mm/min or above. Values below 10 mm/min indicate KCS; values between 10–15 mm/min suggest borderline or early KCS.
Breeds Most Affected by KCS
KCS can affect any dog but is significantly more common in certain breeds with a genetic predisposition to abnormal tear gland development or immune-mediated gland destruction:
- Cavalier King Charles Spaniel: Frequently develops immune-mediated KCS at a relatively young age.
- West Highland White Terrier (Westie): High prevalence of early-onset KCS.
- Shih Tzu and Lhasa Apso: Brachycephalic anatomy increases exposure of the cornea, compounding tear film inadequacy.
- Cocker Spaniel: Both English and American varieties have elevated risk.
- Pug and Bulldog: Protruding eyes and shallow orbits increase evaporative tear loss.
- Yorkshire Terrier, Miniature Schnauzer, Dachshund: Moderately elevated risk.
Large breeds can also develop KCS but at lower rates. Male and female dogs are affected equally.
Causes of Dry Eye in Dogs
The most common cause of canine KCS — accounting for roughly 80% of cases — is immune-mediated destruction of the lacrimal glands. The immune system mistakenly attacks tear-producing tissue, gradually reducing its function. Why this occurs is not fully understood, but genetic predisposition plays a clear role.
Other causes include:
- Distemper virus: Canine distemper can permanently damage the lacrimal glands. This is more common in unvaccinated dogs.
- Drug toxicity: Sulfonamide antibiotics (such as trimethoprim-sulfa) are a well-documented cause of KCS in dogs, sometimes causing permanent gland damage even after the drug is stopped.
- Surgical removal of the third eyelid gland: The third eyelid (nictitating membrane) contains a gland that produces 30–40% of the total tear volume. Removing this gland — sometimes done incorrectly when treating cherry eye — causes KCS.
- Neurological causes: Damage to the facial nerve reduces tear production by eliminating the nerve signals that stimulate the lacrimal gland. This often causes dry eye on only one side.
- Hypothyroidism: Thyroid hormone deficiency can impair tear production as one of several systemic effects.
- Congenital hypoplasia: Some dogs are born with underdeveloped lacrimal glands. Yorkshire Terriers are particularly prone to this form.
Signs and Symptoms
KCS causes a characteristic set of signs that owners often notice before a formal diagnosis:
- Thick, yellowish or greenish discharge: The body compensates for lack of watery tears by overproducing the mucous layer. This sticky discharge accumulates in the corners of the eyes and on fur around them.
- Red, inflamed eyes (conjunctivitis): Constant irritation causes the whites of the eyes and inner eyelids to appear red.
- Squinting or pawing at eyes: Pain from corneal irritation causes the dog to partially close the affected eye or rub at it.
- Dull, cloudy cornea: Chronic dryness causes the normally clear cornea to become opaque. In long-standing cases, brown pigment (melanosis) and blood vessels grow into the cornea, impairing vision.
- Recurrent corneal ulcers: The dry cornea is prone to scratching and infection, leading to painful ulcers.
- Sensitivity to light: Photophobia is common in dogs with corneal involvement.
Treatment and Management
KCS is a chronic condition that typically requires lifelong treatment, but with appropriate management, most dogs maintain good quality of life and preserved vision.
Cyclosporine ophthalmic solution or ointment (Optimmune) is the cornerstone of treatment for immune-mediated KCS. Cyclosporine suppresses the immune attack on the lacrimal glands and directly stimulates tear production. Most dogs show improvement within 4–8 weeks. It must be applied twice daily, usually for life. Approximately 70–80% of dogs respond well.
Tacrolimus eye drops are used in dogs that do not respond to cyclosporine. Tacrolimus is a more potent immunomodulator and is often effective in cyclosporine non-responders.
Artificial tears / lubricating eye drops supplement natural tear production and reduce friction. They are used multiple times daily — often 4–6 times or more — as an adjunct to cyclosporine or in mild cases. Hyaluronic acid-based drops are particularly effective at retaining moisture.
Antibiotic eye drops or ointments treat secondary bacterial infections, which are common given the compromised eye surface. These are used alongside primary treatment, not as a standalone solution.
Parotid duct transposition (PDT) is a surgical option for severe cases where medical treatment fails. The parotid salivary duct is repositioned to drain saliva onto the eye surface instead of into the mouth, using saliva as a tear substitute. It is effective but has drawbacks — saliva doesn’t fully replicate tears and may cause mineral deposits on the cornea.
Regular monitoring with Schirmer Tear Tests every 3–6 months tracks treatment effectiveness and guides dose adjustments.