Follicular Conjunctivitis

By Malcolm Weir, DVM, MSc, MPH; Catherine Barnette, DVM

What is follicular conjunctivitis?

Follicular conjunctivitis is an allergic eye condition of young dogs. It is most commonly seen in large-breed dogs under 1-2 years of age. This condition can also affect cats, although this is less common.

The term conjunctivitis refers to inflammation of the conjunctiva, which is the pink tissue that surrounds the eye, covering the inside of the eyelids and the third eyelid. In the conjunctiva, there are clusters of immune cells known as lymphoid follicles. The lymphoid follicles are a part of your dog’s immune system, responding to infections and foreign materials within the eye. If these immune cells become overstimulated, however, the follicles can become enlarged. This is called follicular conjunctivitis.

What causes follicular conjunctivitis?

Follicular conjunctivitis is typically caused by allergens such as dust, grass, and weeds. Immune stimulation causes the lymphoid follicles on the eye to become enlarged. As the follicles become more and more enlarged, the raised follicles themselves can cause further irritation to the eye, creating a vicious cycle.

"Immune stimulation causes the lymphoid follicles on the eye to become enlarged."

Follicular conjunctivitis is seen most commonly in large-breed dogs, especially those with large eyelid openings, droopy eyelids, or deep-set eyes. This type of eye anatomy allows more debris, pollen, and plant material to enter the eye, irritating the conjunctiva.

Less commonly, follicular conjunctivitis can also be triggered by a bacterial or viral infection. Any prolonged inflammation within the eye, regardless of cause, can trigger follicular conjunctivitis.

What are the signs of follicular conjunctivitis?

If your pet has follicular conjunctivitis, the affected eye(s) will likely appear red and irritated. You may notice increased eye discharge, which may vary from clear to yellow in color. Your pet may squint more than usual and you may notice pawing or rubbing at the eye(s).

How is follicular conjunctivitis diagnosed?

Your veterinarian can usually diagnose follicular conjunctivitis on the basis of an exam. Your veterinarian may numb the eye to allow a closer exam of the eye, including the rear (internal) surface of the third eyelid. Pets with follicular conjunctivitis often have raised bumps (like cobblestones) on their conjunctiva, which are visible upon close examination.

In some cases, your veterinarian may collect cells from one of the raised follicles and examine these cells under a microscope. This can confirm the diagnosis of follicular conjunctivitis.

How is follicular conjunctivitis treated?

Mild cases of follicular conjunctivitis do not require treatment. This is a normal response of the eye to immune stimulation and does not necessarily need to be corrected or prevented.

If your pet is uncomfortable, however, your veterinarian will likely prescribe steroid-containing eye drops or ointment to decrease the inflammation. More recently, some eye specialists have also used non-steroidal anti-inflammatory drugs (NSAIDs) to reduce inflammation. In most cases, follicular conjunctivitis responds quickly to treatment and medications can be gradually tapered over time.

Your veterinarian may also recommend flushing the eye with saline, on a one-time or repeated basis. Flushing the eyes helps to remove debris and allergens that may be affecting the eye. For some dogs, saline flushing alone is enough to treat this problem and prevent recurrence.

"Flushing the eyes helps to remove debris and allergens that may be affecting the eye."

In severe cases, your veterinarian may debride the affected tissue. This involves scraping off portions of the abnormally raised lymphoid follicles. It is important not to remove all of the lymphoid tissue, as it plays an important role in the immune system but removing some tissue may make your pet more comfortable. Your pet will be maintained on steroids after debridement, in order to eliminate remaining abnormal tissue and prevent recurrence.

What is the prognosis for follicular conjunctivitis?

The prognosis for follicular conjunctivitis is good. The disorder rarely has long-term effects on a pet’s vision. Recurrence is common, however. Your pet may require several courses of treatment.

Many young dogs eventually outgrow follicular conjunctivitis. If your dog continues to experience flare-ups into adulthood, it may be helpful to attempt to identify and eliminate the offending allergen. This is not always practical, however, and some dogs must be maintained on periodic medication.

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