Health & Diseases

Conjunctivitis in Dogs: Causes, Symptoms, and Treatment

Conjunctivitis is an inflammation of the conjunctiva – the transparent mucous membrane tissue that covers the eyeball and the inner surface of the eyelids. It is one of the most common reasons for ophthalmological presentations in small animal practice.

Conjunctivitis in Dogs: Causes, Symptoms, and Treatment

What is conjunctivitis in dogs?

Conjunctivitis is an inflammation of the conjunctiva—the transparent mucous membrane that covers the eyeball and the inner surface of the eyelids. It is one of the most common reasons for veterinary visits in small animal practice.

Conjunctivitis is not a diagnosis in itself, but rather a clinical sign: redness and swelling of the conjunctiva, eye discharge (ranging from serous to mucopurulent), and frequent blinking can have many causes—from infections and allergies to dry eye syndrome (KCS). Treatment without determining the underlying cause is not effective.

Background + Scientific Context

Pumphrey et al. (2016, Veterinary Ophthalmology, PubMed 26919768) examined dogs with immune-mediated keratoconjunctivitis sicca (KCS) for concurrent immune disorders: 79% of the dogs with KCS had at least one other immune-mediated disorder, including hypothyroidism, pemphigus, and diabetes. KCS—dry eye caused by lacrimal gland insufficiency—is thus one of the most common systemic causes of chronic conjunctivitis in dogs.

Ledbetter et al. (2009, Veterinary Ophthalmology, PubMed 19614852) documented naturally occurring infections with canine herpesvirus-1 (CHV-1) in adult dogs: CHV-1 can cause conjunctivitis, stromal corneal ulcers, and uveitis—particularly in immunocompromised animals. A herpesvirus etiology is often not clinically recognized, as CHV-1 is tested for less frequently in dogs than in cats.

Dodi (2015, Veterinary Medicine, PubMed 26998254) summarized the current treatment options for immune-mediated ocular diseases: Ciclosporin A (topical) is the treatment of choice for KCS—the substance stimulates lacrimal gland secretion while simultaneously suppressing the immune response. Long-term use is necessary for many dogs.

Vitomalia-Position

Red, watery eyes are not a harmless everyday symptom that can be treated with over-the-counter eye drops. Untreated or improperly treated conjunctivitis—especially in cases of KCS—can lead to permanent corneal damage within weeks. We recommend: Have any eye changes lasting longer than 48 hours examined by a veterinarian. Self-treatment with human eye drops (which often contain cortisone) is risky for dogs—cortisone can significantly worsen existing corneal ulcers.

When is conjunctivitis a concern in dogs?

  • For redness in one or both eyes accompanied by discharge
  • In cases of recurrent conjunctivitis associated with atopy: allergic conjunctivitis as a subtype
  • In dogs with a known autoimmune disease: KCS as a possible comorbidity
  • After exposure to foreign bodies(grass, sand, dirt): mechanical conjunctivitis
  • As an indication of a systemic disease (hypothyroidism, diabetes, distemper)

Practical application

Common causes at a glance:

Category of causes Typical signs Diagnostics
KCS (dry eye) Thick discharge, corneal opacity Schirmer tear test
Allergic/atopic Bilateral, seasonal, itchy Elimination diet, allergy test
Infectious (bacteria) Mucopurulent discharge Conjunctival swab, culture
CHV-1 Usually unilateral; ulcers may occur PCR from a swab
Mechanical/Foreign Object Sudden onset, unilateral Slit-lamp examination

Basic diagnostic tests at the veterinarian's office: 1. Schirmer tear test (STT) — measures tear production; less than 10 mm/min = suspected KCS 2. Fluorescein test — to rule out corneal ulcers (no corticosteroids if the result is positive) 3. Slit-lamp examination — conjunctival surface, eyelid, cornea 4. Tonometry — Intraocular pressure in cases of suspected glaucoma

Common Mistakes & Myths

  • “Red eyes are caused by drafts or dust—they go away on their own.” Conjunctivitis rarely heals completely without treating the underlying cause. Chronic KCS left untreated leads to progressive corneal damage.
  • “I’ll use the eye drops from last time.” Eye drops containing cortisone are contraindicated for ulcers and significantly worsen the prognosis. New symptoms = new diagnosis.
  • "Conjunctivitis is always contagious." Only the infectious form (bacteria, CHV-1) is potentially contagious. KCS, allergic conjunctivitis, and mechanical conjunctivitis are not contagious.

Current State of Research (2026)

KCS remains the most common cause of chronic conjunctivitis in dogs; topical cyclosporine A and tacrolimus are the standard treatments. New studies are investigating combination immunosuppressive therapies for refractory cases. CHV-1 is increasingly recognized as an underestimated cause of ocular disease in dogs—serological testing is still rare in routine practice.

Frequently Asked Questions

Why does my dog keep getting conjunctivitis?

Recurrent conjunctivitis suggests an untreated underlying cause—most commonly KCS (dry eye), atopy, or an anatomical abnormality (e.g., ectropion, entropion). A thorough ophthalmological examination will determine the underlying cause in each case.

Are over-the-counter eye drops suitable?

Only if there are no corneal ulcers and the product does not contain corticosteroids. Fluorescein staining to rule out ulcers is mandatory before any application of corticosteroids. Without a diagnosis, the following applies: use only normal saline solution for cleaning; do not use antibiotics or corticosteroids without a veterinarian’s instructions.

Which dogs are particularly prone to conjunctivitis?

Bulldogs, Cocker Spaniels, Shih Tzus, and West Highland White Terriers have higher rates of KCS. Brachycephalic breeds (those with flat skulls) are more prone to mechanical conjunctivitis due to insufficient eyelid coverage. Dogs with atopy often exhibit concurrent ocular symptoms.

Related terms

Sources & Further Reading

  1. Pumphrey, S. A., Pizzirani, S., Pirie, C. G., & Needle, D. B. (2016). Immune-mediated keratoconjunctivitis sicca in dogs associated with other immune-mediated diseases: 82 cases. Veterinary Ophthalmology, 19(6), 569–579. https://pubmed.ncbi.nlm.nih.gov/26919768/

  2. Ledbetter, E. C., Riis, R. C., Kern, T. J., Damian, A., & Dubovi, E. J. (2009). Corneal ulceration associated with naturally occurring canine herpesvirus-1 ocular infections in two adult dogs. Veterinary Ophthalmology, 12(4), 252–257. https://pubmed.ncbi.nlm.nih.gov/19614852/

  3. Dodi, P. L. (2015). Immune-mediated keratoconjunctivitis sicca in dogs: current and future treatment modalities. Veterinary Medicine: Research and Reports, 6, 313–323. https://pubmed.ncbi.nlm.nih.gov/26998254/

Wissenschaftliche Einordnung

Pumphrey et al. (2016, Veterinary Ophthalmology, PubMed 26919768) investigated dogs with immune-mediated keratoconjunctivitis sicca (KCS) for concurrent immune diseases: 79% of KCS dogs had at least one other immune-mediated disease, including hypothyroidism, pemphigus, and diabetes. KCS—dry eye due to lacrimal gland insufficiency—is therefore one of the most common systemic causes of chronic conjunctivitis in dogs.

Ledbetter et al. (2009, Veterinary Ophthalmology, PubMed 19614852) documented naturally occurring infections with Canine Herpesvirus-1 (CHV-1) in adult dogs: CHV-1 can cause conjunctivitis, stromal corneal ulcerations, and uveitis—especially in immunosuppressed animals. A herpesvirus etiology is often not recognized clinically, as CHV-1 is less frequently studied in dogs than in cats.

Dodi (2015, Veterinary Medicine, PubMed 26998254) summarized the current treatment options for immune-mediated ocular diseases: Ciclosporin A (topical) is the drug of choice for KCS—the substance stimulates lacrimal gland secretion and suppresses the immune response simultaneously. Long-term use is necessary for many dogs.