Keratoconjunctivitis Sicca (Dry Eye)

Laurie Anne Walden, DVM

Photo by Jennifer Shishmanian on Unsplash

Keratoconjunctivitis sicca (KCS), or dry eye, is common in dogs and can also affect cats. KCS is caused by a problem with the quantity or quality of the tear film. The condition is uncomfortable and can cause blindness. For most patients, KCS is managed with lifelong eye medication.
 
Causes
Tears are produced by glands in the eyelids and third eyelid. The tear film contains water, mucus, and oil. Deficiencies in any of the components of the tear film compromise its functions: lubricating the cornea (the clear structure at the front of the eye), removing debris, and providing nutrition to the cornea.
 
Anything that affects the tear-producing glands can cause KCS. Brachycephalic (flat-faced) animals with protruding eyes that aren’t completely covered by the eyelids also develop KCS symptoms because of excessive water evaporation from the surface of the cornea. These are some of the causes of KCS:

• Immune-mediated inflammation of the tear glands: the most common cause in dogs
• Infection
• Congenital problems with tear gland structure
• Problems with the nerve supply to the eye
• Trauma to the eye
• Endocrine disorders like diabetes and hypothyroidism
• Drug toxicity
• Genetics: dog breeds at higher risk include Cavalier King Charles spaniels, cocker spaniels, English bulldogs, Lhasa apsos, shih tzus, and West Highland white terriers

 
Signs
Animals with KCS typically have thick, sticky eye discharge. The discharge is thick because the watery part of the tear film is decreased or absent, so the tear film that remains is made mostly of mucus and oil. Either 1 or both eyes are affected, depending on the cause of the KCS.
 
Tear film deficiencies increase the risk for corneal ulcers, long-term damage to the cornea, and impaired healing of the cornea. These are signs of KCS and the resulting corneal damage:

• Thick white or yellow eye discharge
• Red eye
• Squinting
• Dark discoloration of the cornea
• Blindness (from corneal damage)

 
Diagnosis
The tear film quantity is measured with the Schirmer tear test, in which a sterile paper strip with measurement markings is placed inside the lower eyelid for 1 minute. The distance that the tear film is absorbed along the strip shows whether the animal has low tear production. Veterinary ophthalmologists use other tests to find out whether a patient has a problem with tear film quality.
 
Treatment
Animals with KCS are treated with a combination of eye medications, most of which need to be applied 2 or 3 times a day. Medications include tear stimulants that reduce immune-mediated inflammation, tear replacements to lubricate the eye, and other medications to treat corneal damage. KCS can be managed but not cured, so medical treatment needs to continue for the rest of the animal’s life.
 
For animals whose KCS doesn’t respond to eye medication, a few surgical options are available. The most common of these is parotid duct transposition, which involves rerouting a salivary duct from the mouth to the inside of the lower eyelid so the animal basically drools onto the eye. This procedure is performed by a veterinary ophthalmologist.
 
Image source: Jennifer Shishmanian on Unsplash

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