Conjunctivitis in Dogs: Causes, Symptoms, Diagnosis, Treatment and Prevention

The conjunctiva plays a role in creating tears, providing protection for the eye from foreign invaders, and healing of the cornea after injury.

It is important to identify and treat conjunctiva problems, because some may indicate generalized disease, while others can lead to blindness if left untreated.

Conjunctivitis is an eye condition characterized by inflammation of the membrane of the conjunctiva that covers the front of the eye and the eyelids.

Although not lethal, pets with suspected conjunctivitis should be examined by a veterinarian as soon as possible, as sight is one of their most important senses.

It can affect one or both eyes, and in addition to causing the usual physical symptoms, pets with pink eye can feel extremely uncomfortable as this condition can be irritating, itchy, and very painful.

It is important to exercise caution around affected pets, as even the meekest cat or dog can become aggressive.

Causes of conjunctivitis in dogs

The causes of conjunctivitis in dogs range from infections to some type of environmental irritant and can include:

Bacterial infection

  • Chlamydophila spp.
  • Mycoplasma spp.
  • Corynebacterium spp.

Fungal infection

  • Aspergillus spp.
  • Curvularia spp.
  • Cryptococcus spp.
  • Blastomyces spp.
  • Acremonium kiliense.

Viral infections

  • Herpesvirus canino.
  • Adenovirus canino.
  • Canine distemper virus.
  • Canine flu virus.

Parasitic infections

  • Thelazia callipaeda.
  • Leishmania chagasi.
  • Dirofilaria repens.


Aerosol powder or toxins.

Allergic processes

Caused by perfumes, aerosol chemicals, and atopy.


Usually from the upper respiratory tract.

eye trauma

Diseases that have caused some damage to the animal’s eye.

Other eye diseases

Like dry eye syndrome.

Genetic diseases

Genetic diseases suffered by the pet.


Clinically affected dogs generally have various symptoms such as:

  • Blephora: This refers to jerky blinking and / or squinting.
  • Redness: Affected pets will have a reddish, moist appearance around the eye.
  • Swelling: A buildup of moist tissue around the eyeball can cause swelling in the eye.
  • Follicle formation: accumulations of lymphoid tissue located on the moist surface of the eyelid cause a cobblestone-like appearance.

They can also present epiphora and photophobia.

Diagnosis of conjunctivitis in dogs

Conjunctivitis is fairly easy to identify as it produces visible signs around the eyes.

A mucus-like discharge usually indicates a bacterial or fungal cause, and can be so thick that it causes the eyelids to stick together.

A clear, watery discharge usually results from an allergy or irritant.

Pus, which may crust over the eye, indicates a bacterial cause, usually Streptococcus or Staphylococcus.

Generally, a visual exam is sufficient to make a diagnosis, although a discharge of mucus may require a Schirmer test, which assesses whether there is sufficient tear production.

To rule out corneal damage or ulceration, a veterinarian may also perform a fluorescein stain, in which a dye is applied to the eye and the affected areas turn green.

However, cytology, culture of possible etiologic agents, such as bacteria or fungi, may be necessary, and polymerase chain reaction tests should be considered if viral agents are suspected.

In cases that do not respond to conventional antimicrobial or anti-inflammatory therapy, a conjunctival biopsy may be considered.

The size of the eye should be examined to exclude an enlarged exophthalmic globe, reduced globe (microphthalmos), orbital cellulitis, and periorbital tumors or a fleshy tooth root abscess.

Conjunctivitis in one eye can be the result of a foreign object, inflammation of the lacrimal sac, or dry eye.


Treatment of conjunctivitis depends on the cause: Bacterial infections can be treated with antibiotics, and fungal infections can be treated with antifungal ointments.

If the conjunctivitis has caused an obstruction in the eye , surgery may be required to clear it.

Some cases can be caused by cancer, so surgical removal of the tumor may be the best course of action.

Prevention of conjunctivitis in dogs

Since pink eye can be caused by a number of factors, it is very difficult to prevent it.

However, because it can be contagious, it is important to isolate the affected pet from other pets.

Keeping your pet’s eyes clean and free of potential irritants is the best way to reduce risk.