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What causes red eyes in dogs?

dog with red eye

Red eyes are common in humans. But red eyes can also affect your dog. And dogs’ red eyes can be a symptom of several conditions that are familiar to the human companions of canines.

Causes of red eyes in dogs

Several conditions can cause red eyes in dogs. Here is a summary of the common causes, plus diagnosis and treatment options.

Dry eye disease (keratoconjunctivitis sicca)

Dry eye disease is frequently diagnosed in older dogs, less often in younger dogs. One of the main symptoms of dry eye disease, officially known as keratoconjunctivitis sicca (or KCS), is redness of the eyes along with frequent blinking, cloudy or gray-looking corneas, and abundant mucus production. 

If your dog has dry eye disease, inflammation can trigger redness of the sclera (the white part of the eye) and the pink tissue around the eye. The conjunctiva is the clear, thin membrane that covers part of the surface of the eye and the inner surface of the eyelids.

When a dog has dry eye disease, they may rub their eyes or squint. If left untreated, the dog may experience cloudiness or pigmentation on the corneal surface of the eye that may cause diminished vision or even total blindness. Low tear production can lead to corneal ulcers or even blindness.

Causes of a dog’s dry eye disease may include:

  • Inflammation of the tear-producing glands

  • Drug toxicity

  • Endocrine disease resulting from a hormonal imbalance

  • Canine distemper, a disease caused by a virus that attacks a dog’s respiratory, gastrointestinal and nervous systems

  • Lack of tear-producing glands at birth

A dog’s dry eye disease is diagnosed through a Schirmer’s Tear Test. In this test, the tip of a small strip of special paper is inserted under a dog’s lower eyelid to measure the amount of moisture generated over a certain period of time.

If it’s discovered that a dog has dry eye disease, they can be treated with artificial tears and possibly prescription medication.

Dogs with conjunctivitis (pink eye)

Conjunctivitis is inflammation of the conjunctiva of your dog’s eyes. Again, the conjunctiva is the clear, thin membrane that covers part of the surface of the eye and the inner surface of the eyelids. Keep in mind that a dog has a third eyelid in the inner corner of the eye that may also become inflamed.

Symptoms of conjunctivitis in your dog may include:

Among the potential causes of conjunctivitis in your dog are:

  • Allergic conjunctivitis, which may be caused by numerous allergens or other irritants, or possibly associated with other allergic conditions such as atopic dermatitis

  • Eyelid or conjunctival tumors

  • Viruses such as canine distemper

  • Breed-specific conditions like nodular episcleritis, an elevated area of inflamed episcleral tissue, which is between the conjunctiva and the sclera (the white part of the eye)

  • Tear film deficiency (such as dry eye disease)

  • Eyelid abnormalities such as entropion

  • Obstructed tear ducts

  • Canine glaucoma and other eye disorders

  • Eye trauma or irritation

A dog’s conjunctivitis can be diagnosed with a thorough eye exam. Tests (such as a Schirmer’s Tear Test), fluorescein dye, biopsy and other medical procedures may be ordered to help confirm a diagnosis.

Treatment of canine conjunctivitis may include topical antibiotics, oral antibiotics, tear-production medication, anti-inflammatory medication or surgery.

SEE RELATED: What causes eye infections in dogs?

Canine glaucoma

Glaucoma, a common cause of blindness in animals and humans, can result in redness in a dog’s eyes. Other symptoms of glaucoma may include tearing, cloudiness, eye enlargement and vision loss.

Dogs may be born with primary glaucoma, but they can also acquire secondary glaucoma. Dog breeds that are prone to primary glaucoma include Basset Hound, Beagle, Chow Chow, Chinese Shar Pei, Cocker Spaniel, Great Dane, Jack Russell Terrier, Norwegian Elkhound, Samoyed and Siberian Husky.

To diagnose glaucoma, a dog must undergo an eye exam. A veterinary professional may use a special instrument called a tonometer or a special lens called a goniolens to closely observe the eyes and optic nerves.

Several medical and surgical treatments are available for glaucoma in dogs, which is incurable and hard to control. These may include prescribing topical medications and replacing an eye with a prosthesis.

SEE RELATED: Cataracts in dogs

Corneal ulcer in dogs

A corneal ulcer — a wound on the surface of the eye — may also lead to redness in a dog’s eye, along with tearing, discharge, squinting or cloudiness of the cornea.

Among the causes of a corneal ulcer are traumatic injury, endocrine disease resulting from a hormonal imbalance, irritation of the cornea by an eyelash or other foreign body, and decreased tear production.

A dye called fluorescein may be used to diagnose a corneal ulcer. Treatment options include medication and surgery.

Distichia in dogs

Distichiasis is an extra eyelash that appears along the upper or lower eyelid; it comes out of the tiny gland ducts which line the lid margins. 

Aside from redness, symptoms of distichiasis squinting, discharge and rubbing. A corneal ulcer also may be a sign of distichiasis.

An eye exam may be coupled with application of a dye called fluorescein to diagnose distichiasis. Treatments for the condition may include topical ointments, surgery, cryotherapy or a laser procedure.

READ NEXT: What Is pigmentary keratitis in dogs?

Dry eye disease or keratoconjunctivitis sicca (KCS). American College of Veterinary Ophthalmologists. September 2020.

Unhappy hormones. Tableland Veterinary Service. March 2019.

Canine distemper. American Veterinary Medical Association. Accessed May 2021.

American Kennel Club. Dog eye infections: symptoms, causes & treatments. April 2015.

Conjunctivitis in dogs. VCA Hospitals. Accessed May 2021.

Episcleritis. American Academy of Ophthalmology, EyeWiki. March 2021.

Episcleritis. Wilmer Eye Institute. Accessed May 2021.

Glaucoma. American College of Veterinary Ophthalmologists. Accessed May 2021.

Corneal ulcer. American College of Veterinary Ophthalmologists. Accessed May 2021.

Distichia or distichiasis in dogs. VCA Hospitals. Accessed May 2021.

Distichia. American College of Veterinary Ophthalmologists. Accessed May 2021.

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