A normal tear film is vital to the health of the surface of the eye.  Tears perform numerous functions including lubricating the eye surface to facilitate blinking, keeping the cornea clear and shiny for normal vision, and fighting off infection with natural antibodies and other proteins.  Deficiency of a healthy tear film is known as keratoconjunctivitis sicca, commonly referred to as “dry eye.”  

Signs of KCS

People with dry eye condition commonly complain of chronic eye redness and / or itchiness or even a burning sensation during blinking.
Dry eye is common in dogs (and does occur in other species) and remains one of the most common causes of chronic canine conjunctivitis.  Although animals cannot report their symptoms, certain signs are highly suggestive of dry eye including:

• red, irritated or bloodshot eyes
• signs of discomfort - squinting, holding the eye(s) closed, pawing at the eyes, or excessively rubbing their eyes on the carpet or against furniture
• thick, “rope-like” discharge on the eye surface and eyelids
• clouding or pigmentation of the cornea
• reduced vision
• corneal ulcers
• conjunctivitis

If dry eye condition is untreated, it is not only chronically painful, but can also lead to potentially vision-impairing consequences.  When the eye surface is dry, it is more prone to injury, including corneal ulcerations.  Corneal ulcerations are erosions (similar to a scratch) on the eye surface.  These are exceptionally painful and, in animals with dry eye, are predisposed to becoming infected with bacteria.  A progressive bacterial infection of the cornea can result in extensive corneal scarring or progress to the development of a perforation (a hole) in the cornea.  Chronic KCS can lead to severe corneal melanosis (discoloration due to accumulation of brown pigment).  This pigmentation in most cases can be permanent and vision loss can result.

Causes

In many cases, the cause for dry eye cannot be determined, however a lack of healthy tear production can result from:

• Immune-mediated inflammation in the tear glands - a breed predisposition in the Bulldog, West Highland White Terrier, Pug, Cocker Spaniel, Shih Tzu, among others
• Congenital abnormality in the development of the tear gland
• Surgical removal of the gland of the third eyelid
• Facial trauma
• Neurologic disorders
• Distemper virus in dogs
• Chronic conjunctivitis - especially in cats (Feline herpesvirus)
• Sulfa drug administration
• Hormonal abnormality (hypothyroidism)

Diagnosis

Diagnosis of dry eye is based on the findings of an eye examination and a test to measure tear production.  This test is called the Schirmer tear test, and involves placement of a small strip of paper beneath the lower eyelid for one minute.  The amount of tears produced is measured against known normal values for the species.

Animals with dry eye condition should also be checked for the presence of corneal ulcers.  This is achieved by performing the Fluorescein Stain test in which a dye is applied to the surface of the eye to aid in detecting surface defects.

Treatment

In almost every case of dry eye, some degree of long-term topical treatment is necessary.  This is a condition that is not usually cured, but one that is controlled with medications over the long haul.  Successful treatment is achieved by meeting three goals:

• Stimulation of natural tear production
• Replacement of the deficient tear film
• Treating secondary eye inflammation or infection

Medical

The cornerstone of therapy for dry eye is the use of lacrimostimulant medications, or medication that stimulates the tear glands to produce more tears.  The most commonly used lacrimostimulant medication is cyclosporine - in the form of an ointment or compounded as a drop.  An alternative medication, tacrolimus, is also increasing in popularity and may be successful for some that have a poor response to cyclosporine.  These medications need to be administered relatively infrequently (usually twice daily) and are generally well-tolerated by most patients.

It can take up to 2 to 3 months to successfully improve tear production with lacrimostimulants.  Therefore, tear replacement products are also required to treat animals with dry eye.  The vast majority of over-the-counter tear replacement products found in local pharmacies are safe to use in pets.  Veterinary ophthalmologists often recommend those products that are thicker or more viscous, as these are soothing and coat the surface of the eye longer than a simple saline drop or eye wash.

Reduction of the inflammation associated with dry eye is often achieved through successful treatment of the tear deficiency.  However, other anti-inflammatories or antibiotics may also be prescribed in some instances to manage inflammation or infection.  In general, as tear production and tear health improve, the associated signs of dry eye dissipate.  

Surgical

While most cases of KCS can be successfully managed with long-term medications, some animals may not respond favorably.  In these cases, surgery may become a consideration.  The surgical procedure most commonly recommended is the Parotid Duct Transposition in which the duct of a salivary gland is re-routed from the mouth to open up and secrete under the eyelid and on to the eye surface.  In essence, the pet's own saliva becomes a source of lubrication for the eye.

Prognosis

Dry eye in most animals carries a good prognosis for successful treatment, but is dependent on the underlying cause.  Treatment is generally most successful if it is diagnosed early and medical therapy is consistently administered as prescribed.