KCS in dogs, short for keratoconjunctivitis sicca, is a chronic condition where the eyes don’t produce enough tears. You’ll more commonly hear it called “dry eye.” Without adequate tear production, the surface of the eye becomes irritated, inflamed, and vulnerable to infection and scarring. Left untreated, it can lead to permanent vision loss.
What Tears Actually Do
A dog’s tear film isn’t just water. It’s a layered coating that protects and nourishes the surface of the eye. The outermost layer traps moisture, the middle watery layer delivers oxygen and nutrients to the cornea, and the innermost layer helps the tear film stick to the eye’s surface. In most cases of KCS, it’s the watery middle layer that drops off, because the glands responsible for producing it are damaged or underperforming. Without that layer, the eye dries out, becomes sticky, and starts to deteriorate.
What Causes It
The most common cause of KCS in dogs is an immune system attack on the tear glands. The body’s own immune cells gradually destroy the tissue that produces tears, leading to a slow decline in tear output over time. This autoimmune form accounts for the majority of cases, and it tends to affect both eyes, though one side is often worse than the other.
Several other things can trigger or contribute to dry eye:
- Medications: Certain antibiotics containing sulfonamides (such as trimethoprim-sulfa combinations) can directly damage tear-producing cells. Research published in JAVMA found that the nitrogen-containing ring structure in sulfonamide drugs has a direct toxic effect on the gland cells that make tears. Other drugs, including atropine, can also reduce tear production.
- Nerve damage: Injury to the nerves that signal tear production, sometimes from ear infections or head trauma, can reduce output on the affected side.
- Removal of a tear gland: If a cherry eye (a prolapsed gland of the third eyelid) was surgically removed rather than repositioned, that eye loses a significant source of tear production.
- Metabolic diseases: Conditions like hypothyroidism and diabetes have been associated with reduced tear production.
Breeds at Higher Risk
KCS has a strong genetic component, and certain breeds are significantly more likely to develop it. The list includes American Cocker Spaniels, Bulldogs, Cavalier King Charles Spaniels, Shih Tzus, Pugs, Lhasa Apsos, West Highland White Terriers, Boston Terriers, Miniature Schnauzers, Pekingese, Bloodhounds, English Springer Spaniels, Samoyeds, and Yorkshire Terriers. If you own one of these breeds, it’s worth being aware of the early signs so you can catch it before the cornea is damaged.
Signs to Watch For
The earliest and most noticeable sign is a thick, yellowish or greenish mucus discharge that clings to the eye and keeps coming back even after you wipe it away. Many owners initially assume this is a simple eye infection, but the discharge in KCS is unusually sticky and ropy because the eye is producing mucus without enough water to flush it away normally.
Other signs include redness and inflammation of the white part of the eye, frequent squinting or blinking, and a dull, lackluster appearance to the cornea. Dogs with dry eye often paw at their face or rub their eyes on furniture. Over time, the cornea responds to chronic dryness by developing dark pigmentation and new blood vessels across its surface. This pigmentation can gradually cover the clear part of the eye and obstruct vision. Corneal ulcers, which are painful open sores on the eye’s surface, are also a common complication because the dried-out cornea is fragile and easily damaged.
How It’s Diagnosed
Diagnosis is straightforward. Your vet will perform a Schirmer tear test, which involves placing a small strip of absorbent paper inside the lower eyelid for one minute. The strip wicks up tears, and the distance the moisture travels is measured in millimeters. A normal result is 15 millimeters or more per minute. Values below that suggest reduced tear production, and consistently low readings confirm KCS. The test is painless, takes about a minute, and gives a clear, objective number to work with.
Your vet will also examine the cornea with a special dye that highlights any ulcers or surface damage, and assess how much pigmentation or scarring has already occurred.
Treatment and What to Expect
The primary treatment targets the root cause: the immune system’s attack on the tear glands. Topical eye drops containing either cyclosporine or tacrolimus work by suppressing the immune cells that are destroying the gland tissue. As the University of Tennessee Veterinary Medical Center explains, these medications are T-cell inhibitors that reduce the autoimmune attack and the inflammation it causes. Over weeks, many dogs begin producing more of their own tears again.
These drops are typically applied once or twice daily, and most dogs need them for life. Stopping the medication usually allows the immune attack to resume, and tear production drops again. In many cases, artificial tear drops or lubricating gels are also used between doses to keep the eye moist, especially early in treatment before the dog’s own tear production improves.
Response to treatment varies. Some dogs show improvement within a few weeks, while others take a month or two before tear production measurably increases. A small percentage of dogs don’t respond well to medical treatment, particularly if the tear glands have already been severely destroyed by the time treatment starts. This is why early diagnosis matters so much.
When Surgery Becomes an Option
For dogs that don’t respond to medication, a surgical procedure called parotid duct transposition can reroute one of the salivary ducts so that saliva, instead of tears, flows over the eye to keep it moist. A retrospective study of 92 eyes found a surgical success rate of 92%. However, complications occurred in about half of cases. Most were manageable with medication, but roughly 39% of complications required additional surgery. One well-known long-term side effect is mineral deposits forming on the cornea and eyelids, because saliva contains calcium and other minerals that tears normally don’t. Despite these trade-offs, the procedure can preserve vision in dogs who would otherwise go blind.
Living With a Dog That Has Dry Eye
KCS is a lifelong condition in most cases, but with consistent treatment, the majority of dogs maintain comfortable, functional eyes. The daily routine of administering eye drops becomes second nature for most owners. Keeping the area around the eyes clean by gently wiping away discharge with a warm, damp cloth helps prevent the buildup of crusty mucus that can irritate the skin.
Regular rechecks with your vet, including repeat Schirmer tear tests, help track whether treatment is working and whether the dose needs adjusting. Dogs whose pigmentation has already spread across the cornea before treatment may not fully regain clear vision, but stopping further progression is still a major win. The earlier KCS is caught and treated, the better the long-term outcome for the eye.