Dry Eye (KCS): Why Treatment Is Usually Lifelong
Thick, sticky eye discharge can be dry eye. Which breeds are most at risk, why the drops usually can't stop, and why a yearly tear test makes sense.
Written by thecanineledger
This page carries no advertising, and nothing on it is for sale.
If your dog is squinting, holding an eye shut, or the eye looks cloudy: see a vet now. Dry eye can cause a deep corneal ulcer, and you can’t tell an ulcer from other painful eye problems at home.
In a study of 363,898 dogs at UK primary-care practices, American Cocker Spaniels had about 52 times the odds of dry eye compared with crossbreds. English Bulldogs had about 38 times, and Pugs about 22 times (O’Neill et al., Journal of Small Animal Practice 2021).
While a sticky eye looks like a minor nuisance, dry eye is a lasting disease that can damage the cornea and, in a few dogs, cost the sight. This page covers what dry eye is, which dogs get it, and why treatment usually continues for life.
1. What dry eye is
The Merck Veterinary Manual’s owner page says “The condition known as dry eye results from inadequate tear production.” Its formal name is keratoconjunctivitis sicca, or KCS (Merck, Disorders of the Nasal Cavity and Tear Ducts in Dogs).
The usual cause. Merck says that “In dogs, it is often associated with an autoimmune inflammation of both the tear and nictitans glands.” The dog’s immune system attacks its own tear glands. A 2015 review says “There are several known causes of KCS in dogs, but the immune-mediated one is the most frequent” (Dodi, Veterinary Medicine: Research and Reports 2015).
Other causes. Merck lists distemper (a viral disease), one class of antibiotics, heredity and injury as less frequent causes. If your dog is on long-term medication and its eyes change, tell your vet.
After cherry eye. Merck notes that dogs with cherry eye “appear to be more likely to develop dry eye (see below) later in life, especially if the gland is removed.”
2. The signs
Merck: “It often causes a persistent, thick eye discharge and reddened eyes. There may also be slow-healing sores and scarring on the cornea.”
The 2015 review lists early signs as squinting from pain, “mucoid to mucopurulent ocular discharge” (sticky or pus-like discharge) and redness. Over time, the cornea can develop scarring and brown pigment.
Ulcers can come first. The 2021 study warns that “Dogs with acute KCS often present clinically with deep corneal ulceration amid few other clinical signs”. That is why a painful eye needs a vet now.
Blindness is uncommon, but possible. The review says “Blindness or even loss of the eye may result from dense corneal opacification or corneal perforation secondary to deep ulceration”. It adds: “Thankfully blindness affects only a small group of animals.”
→ Corneal Ulcers, and Why Flat-Faced Dogs Get Them
3. Which dogs get it
The 2021 UK study found dry eye in 0.40% of dogs. Compared with crossbreds, the breeds with the highest odds were:
- American Cocker Spaniel, about 52 times
- English Bulldog, about 38 times
- Pug, about 22 times
- Lhasa Apso, about 22 times
Face shape and spaniels. Flat-faced dogs had about 3.6 times the odds of dogs with medium-length faces. Spaniels had about 3 times the odds of non-spaniels.
Age. “Advancing age was strongly associated with increased odds.” The median age at first diagnosis was 7.49 years.
Lower risk. Labrador Retrievers and Border Collies had reduced odds.
4. Why treatment is usually lifelong
Merck: “In general, the condition requires longterm—often lifelong—use of eye medications.”
Why it can’t simply stop. Because the immune system keeps attacking the tear glands, treatment works by controlling that attack and replacing moisture. The review describes the main medication’s effects as to “stop the aggression of the lachrymal gland”, reduce the inflammation, and “restore eye lubrication.” Stop the drops, and the attack can resume.
What treatment involves. Merck describes medications to increase tear production, artificial tears to add moisture, and treatment to reduce mucus. “In long-term dry eye resistant to medical therapy, surgery may be required to correct the condition.”
Early diagnosis matters. The review says “an early diagnosis is of vital importance, in particular to give the best possible therapy.”
Our note: “Stop the drops, and the attack can resume” is our explanation of why treatment is often lifelong. Merck says “often lifelong” without giving the reason. Some dogs with other causes may recover.
Our note: These drugs come in different forms and strengths. Don’t switch between them without your vet.
5. The yearly tear test
The tear test is quick: a strip of paper sits inside the lower eyelid for a minute to measure tear production.
The study’s recommendation. The 2021 authors say “Quantitative tear tests are recommended within yearly health examinations for breeds with evidence of predisposition to KCS”. They extend this to dogs “without other suggestive clinical signs of KCS.”
For breeders. The authors note that “most national eye panels for breeding dogs do not include mandatory quantitative tear testing”, and suggest adding it for predisposed breeds.
If you own one of the breeds above, ask for a tear test at your dog’s annual check-up, especially as it gets older.
Our note: Our description of the tear test comes from general knowledge, not a source we read.
→ Preventive Care Without the Upsell: What Your Dog Actually Needs
6. What we could not verify
| Commonly said | What we found |
|---|---|
| “Sticky eyes are just conjunctivitis” | Not always. Persistent thick discharge and red eyes are signs of dry eye. A tear test can tell. |
| “Once it’s better, you can stop the drops” | Usually not. Merck says treatment is often lifelong. |
| “Dry eye always makes dogs blind” | No. The review says blindness affects only a small group of dogs. |
| “Only old dogs get it” | Mostly older dogs. The median age at diagnosis was about 7.5 years, but younger dogs can be affected. |
| “Most drops sold for dry eye are the same” | We found no source we read on this. Don’t switch products without your vet. |
Sources
- O’Neill DG, Brodbelt DC, Keddy A, Church DB, Sanchez RF. Keratoconjunctivitis sicca in dogs under primary veterinary care in the UK: an epidemiological study. J Small Anim Pract 2021: VetCompass, 363,898 dogs; read in full
- Dodi PL. Immune-mediated keratoconjunctivitis sicca in dogs: current perspectives on management. Vet Med (Auckl) 2015: narrative review
- Merck Veterinary Manual: Disorders of the Nasal Cavity and Tear Ducts in Dogs (pet owner version; Gelatt, DACVO; last updated Sept 2024)
Always confirm with your vet before acting on anything on this page.