Keratoconjunctivitis Sicca (Dry Eye) in Dogs: An Overview

Keratoconjunctivitis sicca, commonly called dry eye or KCS, is one of the most frequently diagnosed eye conditions in dogs, caused by inadequate tear production or poor tear quality that leaves the corneal surface unprotected. The immune system attacking a dog’s own tear glands is the most common culprit, though medications, nerve damage, and breed anatomy all play roles. Left untreated, KCS can progress from irritation and discharge to corneal scarring, pigmentation, and even blindness, but the condition is highly manageable when caught early and treated consistently.

Why the Tear Film Matters

A dog’s tear film is not just water sitting on the eye. It has a layered structure with lipids on the outside to slow evaporation, a watery middle layer that carries nutrients and antimicrobial proteins, and a mucin layer closest to the cornea that helps tears stick evenly to the surface.¹ Each layer serves a protective function, and a breakdown in any one of them can produce dry eye symptoms. In most dogs with KCS, the aqueous (watery) layer is deficient because the lacrimal glands are damaged or suppressed. Without that layer, the eye loses its main source of oxygen delivery, waste removal, and infection defense. The cornea becomes vulnerable to bacterial invasion, ulceration, and chronic inflammation.

What Causes Dry Eye in Dogs

The underlying cause matters because it shapes both the prognosis and the treatment approach. The list of known triggers is long, including congenital, metabolic, infectious, drug-induced, neurogenic, radiation-related, and idiopathic causes, but immune-mediated destruction of the lacrimal glands accounts for the vast majority of cases.² In these dogs, the body’s own immune cells infiltrate the tear-producing glands and gradually destroy them. Why this happens in certain dogs and not others is still not fully understood, but breed genetics clearly load the dice.

Drug-induced KCS is the cause most worth knowing about because it is preventable. Sulfonamide antibiotics, commonly prescribed for urinary tract infections, can be toxic to the lacrimal gland with prolonged use.³ Other drugs that affect the autonomic nervous system can also suppress tear production. If your dog is on any long-term medication and you notice increased eye discharge or squinting, bring it up with your vet. Drug-induced KCS can sometimes reverse if the medication is stopped early enough, unlike immune-mediated cases where gland damage tends to be permanent.

Neurogenic KCS is a less common but distinctive form. Dogs with neurogenic dry eye typically have reduced tear production on only one side of the face, and the nostril on the same side is dry as well.⁴ The nerve supplying the lacrimal gland also supplies moisture to the nose, so when that nerve is damaged or dysfunctional, both dry out together. This pattern can actually be a useful diagnostic clue: a dog with one dry, crusty nostril and a goopy eye on the same side probably has a neurogenic cause rather than an immune-mediated one. The treatment overlap is significant, but neurogenic cases sometimes respond to different additional therapies like topical pilocarpine.

Breeds at Higher Risk

KCS does not affect all breeds equally, and the disparities are dramatic. A large epidemiological study of dogs under primary veterinary care in the UK found that American Cocker Spaniels had roughly 52 times the odds of developing KCS compared to crossbred dogs. English Bulldogs were close behind at about 38 times the odds, followed by Pugs at around 22 times and Lhasa Apsos at about 21 times.⁵ On the protective end, Labrador Retrievers and Border Collies had significantly reduced odds.

Two patterns stand out in the breed data. First, brachycephalic dogs (those with shortened skulls and flat faces) had about 3.6 times the odds of KCS compared to dogs with medium-length skulls. Their prominent eyes and wider palpebral fissures expose more corneal surface to the air, which likely increases evaporative tear loss even when tear production is technically adequate. Second, spaniels as a group had about three times the odds compared to non-spaniels, suggesting a genetic vulnerability beyond just skull shape.⁵ If you own a breed in the high-risk category, proactive tear testing during routine exams is worth discussing with your vet. Catching KCS before clinical signs become severe makes treatment far more effective.

Recognizing the Signs

The classic presentation of canine dry eye is a thick, yellowish-green mucoid discharge that owners often mistake for a simple eye infection. Unlike a typical bacterial conjunctivitis, the discharge in KCS keeps coming back even after antibiotic drops because the underlying problem is not infection but dryness. The eye looks red and irritated, the conjunctiva swells, and over time the cornea develops visible changes: blood vessel growth into tissue that should be clear, brown-black pigment deposits, and a dull surface that has lost its normal shine.

Advanced imaging has helped researchers see what happens beneath the surface. Dogs with aqueous-deficient dry eye show an irregular corneal contour, and pigmentation appears as a dense band in the corneal epithelium that blocks the view of deeper structures. Blood vessels that do not belong in the cornea grow in from the edges, a sign the tissue is chronically starved of the oxygen and nutrients that tears normally deliver.⁶ These changes are not just cosmetic; they reduce vision and can become permanent if the dryness goes unchecked.

How Dry Eye Is Diagnosed

The workhorse diagnostic tool for canine KCS is the Schirmer Tear Test (STT-1). A small standardized paper strip is placed in the lower eyelid pouch without anesthesia and left for one minute; the length of the strip that becomes wet, measured in millimeters, gives a direct reading of tear production.⁷ Normal dogs typically produce 15 mm per minute or more. Readings below 15 mm/min are considered suspicious, and readings below 10 mm/min are generally diagnostic for KCS.

A subtle detail worth noting: whether the eyelids are held open or closed during the test actually changes the result. Research comparing open-eye versus closed-eye STT-1 in both brachycephalic and non-brachycephalic breeds found significantly higher values when eyelids were closed. In Shih Tzus, for instance, closed-eye testing averaged about 18.6 mm/min versus 16.3 mm/min with eyes open; in Labrador Retrievers, the gap was even wider, at roughly 21.6 versus 17.8 mm/min.⁸ This matters clinically because a borderline reading could tip one way or the other depending on technique, and consistency between visits is important for tracking whether treatment is working.

Beyond the STT, vets assess tear film breakup time (how quickly bare spots appear on the cornea after a blink), fluorescein staining to check for corneal ulcers, and the degree of conjunctival redness and discharge. Newer diagnostic methods like strip meniscometry, which measures the volume of the tear meniscus along the lower lid margin, correlate well with STT-1 results in dogs with KCS and may offer additional confirmation in ambiguous cases.⁹ Meibomian gland assessment, using infrared imaging to check the oil-producing glands in the eyelids, is also becoming more available in veterinary practice. Healthy dogs already show some degree of meibomian gland loss, with median loss around 25-26% in both upper and lower lids in one study, so interpreting these images requires breed-appropriate baselines.¹⁰

Treatment With Immunomodulatory Drugs

Since most canine KCS is immune-mediated, the cornerstone of treatment is not just replacing tears but suppressing the immune attack on the lacrimal glands. Cyclosporine A (CsA) has been the first-line immunomodulatory drug for decades. Applied topically as an ointment or drop, it calms the immune assault on the glands and allows surviving glandular tissue to resume producing tears. In one study, Schirmer test values improved significantly after two months of cyclosporine treatment, with readings rising from below 13 mm/min to above 15 mm/min in all treated animals.¹¹

When cyclosporine does not produce an adequate response, tacrolimus is the usual next step. It works through a similar immunosuppressive pathway but is often effective in dogs that did not improve on cyclosporine. One study using 0.02% tacrolimus found that tear production increased by at least 5 mm/min in about 85% of eyes in the mildest KCS category, and even in more advanced cases, roughly half of eyes showed meaningful improvement.¹² Separate research confirmed that tacrolimus at 0.03% in olive oil successfully increased tear production in dogs that had already failed cyclosporine therapy.¹³

A critical point that owners need to understand: immunomodulatory treatment for KCS is almost always lifelong. Research tracking what happens when treatment is stopped found that half of the eyes studied experienced a drop in tear production to below 10 mm/min within about three weeks of discontinuation, accompanied by a return of severe clinical signs. The other half maintained adequate tear production for the full follow-up period, but dogs that had lower baseline values before starting treatment and more severe disease were the ones most likely to relapse quickly.¹⁴ Stopping drops because the eyes “look better” is one of the most common mistakes owners make. The eyes look better because the drops are working, and in most cases the glands have not healed enough to function independently.

Artificial Tears and Lubricants

While immunomodulatory drugs address the cause, artificial tears provide symptomatic relief by physically replacing the missing moisture on the eye surface. They are used alongside cyclosporine or tacrolimus, not as a substitute. Not all artificial tears are equal, though. A prospective study comparing hyaluronic acid-based drops to carbomer-based gels in dogs with KCS found that hyaluronic acid drops significantly reduced conjunctival redness and eye discomfort compared to the gel formulation, even when the gel was used at equal or greater frequency. The actual increase in tear production was minimal and not clinically meaningful, which underscores that artificial tears are comfort measures, not disease modifiers.¹⁵ They buy time and reduce surface damage while the immunomodulatory drug does the heavy lifting.

When Surgery Becomes Necessary

Some dogs do not respond adequately to any medical therapy. Their lacrimal glands are too damaged to recover, and the eye remains chronically dry despite maximal drug treatment. For these cases, parotid duct transposition (PDT) is the established surgical option. The procedure reroutes the duct of the parotid salivary gland, which normally empties saliva into the mouth near the upper cheek teeth, so that it instead delivers fluid to the eye. Saliva is not identical to tears, but it provides enough moisture to keep the cornea from drying out.

A retrospective review of 92 eyes that underwent PDT found that the procedure improved ocular comfort and vision in medically refractory cases, and owners generally perceived it as successful. About a third of cases required some ongoing management afterward, such as wiping mineral deposits from the eyelids caused by the slightly different composition of saliva compared to tears.¹⁶ The deposits are a cosmetic nuisance more than a medical problem, and most owners find them a worthwhile trade-off for a comfortable, sighted eye.

Researchers have also investigated the anatomy of the minor salivary glands in the dog’s lip and cheek area as potential alternative tissue for surgical approaches. These glands are small, arranged in a single row along the dental line, and vary considerably in volume between individual dogs.¹⁷ Whether minor salivary gland transplantation could become a practical clinical procedure remains to be seen, but the anatomical groundwork is being laid.

Stem Cell Therapy and Other Emerging Approaches

The most actively researched frontier in canine KCS treatment is mesenchymal stem cell (MSC) therapy. The concept is appealing: instead of suppressing the immune attack and hoping the remaining gland tissue is enough, stem cells might regenerate or protect the gland itself. Early clinical work has been encouraging. In one study, a single injection of one million allogeneic stem cells directly into the lacrimal glands produced a statistically significant increase in tear production and improvement in ocular surface health across all treated eyes. Dogs with mild-to-moderate KCS saw their tear values return to healthy levels, while severely affected dogs improved but did not fully normalize.¹⁸ No adverse effects were observed, and the benefits lasted up to 12 months from a single treatment, a major practical advantage over daily eye drops.

A systematic review and meta-analysis that pooled data across stem cell studies confirmed the direction of these findings but added important context. The average increase in tear production was modest: about 0.7 mm/min at one month and 1.5 mm/min at six months. The treatment was consistently safe and did improve ocular comfort scores, but the clinical significance of those tear production gains is debatable given that many dogs need increases of 5 mm/min or more to reach healthy levels.¹⁹ Stem cell therapy is not yet ready to replace cyclosporine or tacrolimus for most dogs, but it may eventually serve as an adjunct or as a treatment for dogs that do not respond to conventional drugs.

Another experimental avenue involves conditioned media from amniotic stem cells. Rather than injecting live cells, this approach uses the bioactive molecules that stem cells secrete, delivered as eye drops. Early results in a small group of dogs showed that half of the treated animals had increased tear protein levels, reduced inflammatory markers, and improved tear production.²⁰ These are preliminary findings, but the idea of a biologic eye drop that combines the convenience of topical treatment with some of the regenerative properties of stem cells is compelling for owners who struggle with daily medication compliance or whose dogs have advanced disease.

Living With a Dog That Has KCS

The day-to-day reality of managing canine dry eye is mostly about consistency. The immunomodulatory drops need to go in on schedule, typically twice a day, and artificial tears may be needed between doses depending on severity. Most owners find a routine within a week or two, and many dogs tolerate the drops remarkably well once they associate them with the relief that follows. Cleaning the discharge before applying drops makes a difference, since the thick mucus that accumulates can physically block medication from reaching the eye surface. A warm, damp cloth works fine for this.

Flare-ups can still happen even on treatment. Windy or dry environments, air conditioning, and car rides with windows open all increase evaporative stress on the eye. Some dogs benefit from wearing doggles or protective eyewear in these situations, though that requires a cooperative patient. Seasonal allergies can compound the inflammation, and dogs with both KCS and atopic dermatitis tend to have worse eye symptoms during allergy season. If you notice increased discharge or redness that does not settle within a day or two, a vet visit is warranted to check for corneal ulcers, which can develop quickly in a dry eye and escalate into an emergency if they perforate.

One of the more frustrating aspects of KCS for owners is the cost of long-term medication, especially for tacrolimus, which is typically compounded by a specialty pharmacy. Compounded formulations vary in quality and shelf life, so working with a reputable compounding pharmacy matters. Some owners have success with generic cyclosporine formulated for veterinary use, which can reduce costs substantially compared to branded products. Discussing pricing options openly with your vet is worth doing early, since the financial sustainability of treatment directly affects whether it stays consistent over the years your dog will need it.

The Overlap With Human Dry Eye Research

Canine KCS is not just a veterinary concern in isolation. Dogs with naturally occurring dry eye serve as one of the closest spontaneous animal models for human Sjögren syndrome and other forms of autoimmune dry eye. Much of the early clinical evidence for cyclosporine’s effectiveness in dry eye came from veterinary trials, and the drug’s eventual approval for human use was informed by that work. The same flow continues today: stem cell therapies and novel biologics are being tested in dogs partly because their disease mirrors the human condition in ways that laboratory models cannot replicate. The research benefits both species, and veterinary ophthalmology journals regularly publish work that human dry eye researchers cite. If your dog’s vet mentions a treatment that sounds cutting-edge, there is a reasonable chance it originated from or was validated in work that crosses between human and veterinary medicine.