Keratoconjunctivitis Sicca (Dry Eye) in Dogs

It's not just cataracts or conjunctivitis that can affect our dogs' eyes — there are many other equally common conditions that, if not treated in time, can be fatal for their vision.

Keratoconjunctivitis sicca (dry eye) is a condition that's certainly not at the back of the line among eye clinic visits. At Soyunperro we'll go over what it is, its causes, the types that exist, its characteristic symptoms, and how it's treated.

What Is Keratoconjunctivitis Sicca?

To understand this condition itself, we first need to understand eye lubrication, and more specifically that of the cornea (the outermost layer of the eye). The eye's surface is covered by a tear film, which serves important functions in the cornea's physiology and protection. These are:

• Providing a medium for transporting oxygen, glucose, electrolytes, water, antibodies, and defensive inflammatory cells.
• Lubricating the eyelids as they move over the eye's surface.
• Flushing harmful substances away from the eye's surface.

Knowing this, keratoconjunctivitis sicca is the name given to the inflammatory and degenerative process affecting the cornea and conjunctiva, caused by deficient tear production. It's a relatively common disease in dogs, and often its cause or etiology can't be determined. Although we'll look at the types below, it likely has an immune-mediated origin.

Types of Keratoconjunctivitis and Origin

Cases of keratoconjunctivitis sicca can be classified as congenital or acquired.

• Congenital: presents as persistent dryness of the conjunctiva and corneal opacity. It normally affects only one eye, and the cause is underdeveloped tear glands, or a lack of them, so proper tear secretion doesn't occur. Breed predisposition is found in: West Highland White Terrier, Miniature Schnauzer, Chihuahua, English Bulldog.
• Acquired: this type of keratoconjunctivitis sicca can have several causes, since it develops over the course of the animal's life rather than being present from birth, as in the congenital form.

Among the acquired forms, we find:

1. Iatrogenic: caused by drugs such as atropine over long periods, sulfadiazine, sulfamethoxazole, and sulfasalazine. Tear production generally recovers once treatment is stopped.
2. Infectious: the infectious agent most often linked to the development of this condition is the distemper virus. That said, if the animal recovers from this disease, tear production returns.
3. Traumatic and neurological: can be caused by eye trauma, or, for example, by ear infections or nervous system damage.
4. Senile atrophy: the tear gland gradually atrophies with age.
5. Immune-mediated: due to autoantibodies directed against cells in the tear ducts. This can occur in: lupus erythematosus, rheumatoid arthritis, autoimmune hemolytic anemia, and chronic active hepatitis.

How to Know If a Dog Has Keratoconjunctivitis? Symptoms

Signs will depend on whether the keratoconjunctivitis is chronic or acute. Let's look at both types.

1. Acute keratoconjunctivitis sicca: characterized by the appearance of mucopurulent discharge (pus and mucus), a dry, dull, matte cornea, and sometimes the development of central corneal ulcers.
2. Chronic keratoconjunctivitis sicca: characterized by conjunctival hyperemia (inflammation), mucopurulent eye discharge, and chemosis or edema (surface fluid buildup). Over time, crystalline and melanin deposits (dark) develop, which can lead to blindness from corneal opacity.

Diagnosis of Keratoconjunctivitis Sicca

A diagnosis of keratoconjunctivitis sicca can be made through a good history the vet takes about our pet and an ophthalmological exam. However, a definitive diagnosis is only possible through the Schirmer test, which quantitatively assesses tear production.

To perform this test, the vet will use special white paper strips folded 5 mm at one end, placed in the lower conjunctival sac while the animal keeps its eyes closed. After a minute, the moistened part of the paper is measured from the fold.

Values considered normal in dogs are twenty/twenty-five millimeters in one minute (measured on the previously placed paper). When the Schirmer test result is below ten millimeters in one minute, keratoconjunctivitis sicca is present. It's considered very severe if tear production is under five millimeters.

Treatments for Keratoconjunctivitis Sicca

Treatment for keratoconjunctivitis sicca is mainly based on giving topical cyclosporine A. This drug is a non-cytotoxic immunosuppressive agent (it doesn't cause cellular damage), which regulates the immune response toward immune tolerance. This treatment also increases tear production within two to three weeks.

Most animals need this treatment for life. How successful treatment is will depend on the severity of the disease. In animals with tear production between zero and one millimeter on the Schirmer test, the response to treatment tends to be low (only thirty percent will respond to treatment).

Cyclosporine A therapy should be paired with artificial tears until tear production is restored, along with eye rinses to remove buildup of discharge or exudate, as well as topical antibiotic therapy to control any bacterial conjunctivitis that may occur.