What Eye Discharge Tells You
The color and consistency of eye discharge provides important diagnostic information.
Clear, watery discharge (epiphora). Excessive tearing that may stain the fur below the eyes reddish-brown (tear staining). Most commonly due to anatomical factors (shallow eye sockets in brachycephalic breeds, blocked tear ducts), minor irritation, or allergies. Usually not medically serious.
White or gray mucoid discharge. A small amount of mucoid discharge in the morning (sleep crusts) is normal. Excessive white mucoid discharge can indicate dry eye (keratoconjunctivitis sicca/KCS), allergic conjunctivitis, or early infection.
Yellow or green purulent discharge. Indicates bacterial infection. Bacterial conjunctivitis, corneal ulcer with secondary infection, or dacryocystitis (tear duct infection) are the primary causes. Requires veterinary treatment with appropriate antibiotics.
Bloody discharge. Suggests trauma, foreign body, glaucoma, clotting disorder, or intraocular tumor. Requires urgent evaluation.
Possible Causes Ranked by Likelihood
Common Causes
Allergic conjunctivitis. Redness, swelling, and clear to white discharge from atopic dermatitis affecting the eyes. Seasonal pattern is typical. Often accompanies skin allergy signs (paw licking, scratching). Both eyes are usually affected. Treatment targets the underlying allergy.
Anatomical epiphora (tear staining). Brachycephalic breeds (Pugs, French Bulldogs, Shih Tzus) have shallow eye sockets and prominent eyes that produce excessive tearing. Small breeds (Poodles, Maltese, Bichon Frises) commonly have tear staining from narrowed or blocked nasolacrimal ducts. The tears are normal; they just overflow because the drainage system cannot keep up or is malformed.
Conjunctivitis (pink eye). Inflammation of the conjunctival membranes. Causes include bacteria, viruses, allergens, irritants, and dry eye. Signs: redness, swelling, discharge (character depends on cause), squinting, and rubbing. Both eyes are usually affected in allergic and viral causes; one eye may be affected first in bacterial causes.
Foreign body or irritant. Dust, sand, plant material, or hair can irritate the eye surface, producing tearing, squinting, and secondary discharge. Cocker Spaniels and other breeds with prominent facial hair are susceptible to hair rubbing on the cornea.
Moderately Common
Dry eye (keratoconjunctivitis sicca/KCS). The tear glands produce insufficient tears, resulting in thick, sticky, yellow-green discharge with a dry, dull corneal surface. The eye is chronically irritated because it lacks the protective tear film. Immune-mediated destruction of the tear glands is the most common cause. Cocker Spaniels, English Bulldogs, West Highland White Terriers, Cavalier King Charles Spaniels, and Shih Tzus are predisposed. Diagnosed with a Schirmer tear test. Requires lifelong treatment with immunomodulatory eye drops (cyclosporine or tacrolimus).
Corneal ulcer. A scratch or abrasion on the corneal surface produces pain, squinting, tearing, and secondary bacterial infection with yellow-green discharge. Can result from trauma, foreign body, dry eye, or entropion (eyelid rolling inward). Diagnosed with fluorescein stain. Superficial ulcers heal within 5-7 days with treatment. Deep ulcers or descemetoceles are surgical emergencies.
Entropion. Inward rolling of the eyelid, causing the lashes and lid hair to rub against the cornea. Produces chronic tearing, squinting, and discharge. Common in Shar-Peis, English Bulldogs, and Rottweilers. Surgical correction is curative.
Less Common but Serious
Glaucoma. Elevated intraocular pressure causes pain, redness, a cloudy or blue-tinged cornea, a dilated pupil, and tearing. Cocker Spaniels, Beagles, Basset Hounds, and Siberian Huskies are predisposed. Glaucoma is a medical emergency since elevated pressure rapidly destroys the retina, causing permanent blindness within 24-48 hours without treatment.
Cataracts. Lens opacity does not typically cause discharge but can cause secondary uveitis (intraocular inflammation) that produces tearing and redness. Common in diabetic dogs and certain predisposed breeds.
Uveitis (intraocular inflammation). Inflammation inside the eye from infection, immune-mediated disease, trauma, or lens protein leakage. Produces pain, redness, tearing, constricted pupil, and cloudiness. Requires aggressive anti-inflammatory treatment to prevent secondary glaucoma and blindness.
Severity Scale
Normal (No Concern)
- Small amount of clear tearing or morning eye crusts
- Mild tear staining in a brachycephalic or small breed
- Brief tearing after wind or dust exposure
Call Your Vet (Within Days)
- Persistent yellow or green discharge
- Red, swollen conjunctiva with discharge
- Excessive clear tearing beyond normal for the breed
- Squinting or rubbing the eye persistently
- Change in the appearance of the eye (cloudiness, color change)
Emergency (Go Now)
- Sudden onset of severe squinting, tearing, and redness (corneal ulcer or glaucoma)
- Blue or cloudy eye with visible pain (glaucoma)
- Visible foreign object in or on the eye
- Bleeding from the eye
- Sudden bulging of the eye (proptosis) or facial swelling around the eye
- Eye that appears larger than normal (glaucoma)
Home Care
- Gentle cleaning. Wipe discharge from around the eyes with a soft, damp cloth or cotton pad moistened with warm water. Wipe from the inner corner outward. Use a separate cloth for each eye to prevent cross-contamination
- Tear stain management. Keep the area below the eyes clean and dry. Trim stained fur carefully. Tear stain supplements (containing tylosin) are available but work inconsistently
- Do not use human eye drops (Visine, Clear Eyes) without veterinary guidance. These contain vasoconstrictors not intended for dogs
- Saline rinse. Sterile saline (not contact lens solution) can be used to flush mild irritants from the eye
- Prevent rubbing. If the dog is pawing at its eye, an Elizabethan collar prevents further damage
- Environmental management. In dogs with allergic conjunctivitis, wiping the face and eyes after outdoor excursions removes surface allergens
Breed Predispositions
- Pugs and French Bulldogs: prominent eyes prone to corneal ulcers, chronic epiphora, KCS
- Cocker Spaniels: KCS (dry eye), glaucoma, chronic conjunctivitis
- Shih Tzus: KCS, epiphora, corneal ulcers from shallow orbits
- Poodles and Maltese: tear staining from nasolacrimal duct issues
- Shar-Peis: entropion causing chronic corneal irritation
Longevity Connection
Vision is a critical component of quality of life in aging dogs. Preventable causes of blindness (untreated glaucoma, chronic dry eye, progressive ulceration) reduce independence, increase anxiety, and accelerate cognitive decline. Breed-specific eye screening (available through the Orthopedic Foundation for Animals and board-certified veterinary ophthalmologists) identifies treatable conditions before they cause irreversible damage. For breeds with known eye disease predisposition, annual ophthalmologic examination is a high-value longevity investment.
Frequently Asked Questions
Is tear staining harmful to my dog? Tear staining itself (the reddish-brown discoloration below the eyes) is cosmetic and not harmful. However, the chronic moisture can predispose the skin to secondary yeast or bacterial infection (moist dermatitis). Keep the area clean and dry. If the skin beneath the staining becomes red, irritated, or odorous, veterinary treatment for the secondary infection is needed.
How do I know if my dog has an eye infection? Eye infection signs include: yellow or green discharge (rather than clear), red or swollen conjunctiva, squinting or holding the eye partially closed, rubbing the eye on surfaces or with paws, and a change in the eye’s appearance (cloudiness, color change). Clear discharge alone is usually not infection. If you see colored discharge, schedule a veterinary appointment.
Can I use human eye drops for my dog? Do not use human eye drops without veterinary guidance. Products like Visine contain vasoconstrictors (tetrahydrozoline) that are not intended for dogs and can mask symptoms while the underlying condition worsens. Artificial tears (preservative-free) are generally safe for moisturizing and can be used while awaiting a veterinary appointment.
What causes chronic dry eye in dogs? The most common cause is immune-mediated destruction of the lacrimal (tear) glands. The immune system attacks and progressively destroys tear-producing tissue. Certain breeds have genetic predisposition. Other causes include drug reactions (sulfonamide antibiotics), viral infection (distemper), hypothyroidism, and nerve damage. KCS requires lifelong treatment with immunomodulatory drops (cyclosporine or tacrolimus).
Should I worry if only one eye has discharge? Unilateral (one-eye) discharge is actually more concerning than bilateral discharge in some ways, as it suggests a localized cause: foreign body, corneal ulcer, blocked tear duct, or early infection. Bilateral discharge is more commonly allergic or viral. Either pattern warrants veterinary evaluation if the discharge is persistent, colored, or accompanied by squinting or redness.
References
- Maggs DJ, Miller PE, Ofri R. “Slatter’s Fundamentals of Veterinary Ophthalmology.” 6th ed. Elsevier. 2018.
- Gelatt KN. “Essentials of Veterinary Ophthalmology.” 3rd ed. Wiley-Blackwell. 2014.
- Williams DL. “Immunopathogenesis of keratoconjunctivitis sicca in the dog.” Veterinary Clinics of North America: Small Animal Practice. 2008;38(3):513-528.
- Plummer CE, et al. “The canine glaucomas.” Textbook of Veterinary Internal Medicine. 8th ed. 2017.
This content is for informational purposes only and does not constitute veterinary advice. If your dog is showing signs of illness, consult a licensed veterinarian.