Keratoconjunctivitis sicca. KCS.
Or, dry eye, as it’s commonly known.
Broken down, the first word refers to the parts of the eye usually affected in the condition. “Kerato” refers to the cornea, or clear part of the eye. “Conjunct” refers to the conjunctiva, the thin tissue that covers and protects the rest of the eye. “Itis,” as we’ve discussed previously, means inflammation. “Sicca” refers to dryness.
A normal tear film in dogs consists of three layers, much like a sandwich. On the outside and inside of the sandwich is two different types of mucus. The inner layer is serous, or watery. The serous layer makes up the bulk of the volume and provides lubrication as well as immune system products that protect the health of the eyes.
KCS results in a loss of serous tear production due to an immune system invasion of the tear glands. Both kinds of mucus continue to be produced in normal quantities.
One of the first complaints from pet owners in a KCS patient is that there is “sleep” or “goop” in the eyes all of the time. This occurs because one of the serous layer’s jobs is to wash away the two kinds of mucus. With nothing to wash it away, the mucus simply builds up.
Another common sign is itchiness of the eyes, which, being dry, hurt with every blink.
Tear production in dogs is measured by the Schirmer Tear Test (STT). A special standardized paper is introduced between the lower lid and eyeball and tears are allowed to move down the paper by capillary action for one minute. Schirmer tear strips are calibrated in millimeters (mm) and normal tear production is between 14 and 20 mm production in 60 seconds. Practically speaking, some patients become symptomatic even in the 15-18 mm range.
The most common form of KCS occurs when the body’s immune system causes an infiltration of plasmacytes and lymphocytes into tear glands, resulting in a progressively diminishing tear flow.
Certain medications, especially those in the sulfonamide family and some non-steroidal antiinflammatory drugs (NSAIDS) can also result in KCS.
Patients with low thyroid function are also likely to experience KCS.
Some systemic diseases can trigger an attack on the tear glands, as can neurological conditions. Surgery that damages nerves to the area can be a cause, as can surgical removal of the gland of the third eyelid, which is responsible for a significant portion of the serous tear film. Thirty years ago it was common to remove this gland when it prolapsed, causing a condition colloquially known as “cherry eye.” Now a better surgical procedure is used that “buries” the gland below the lid margin but allows its tear production to continue to flow onto the globe (eyeball).
Certain breeds are predisposed to the condition, including the West Highland White terrier, cocker spaniel, bulldog and Lhasa apso. Females are overrepresented.
Sequella include pain, infections, pigmentation of the cornea and blindness. Being an “itis” disease, the body feels obligated to respond to the inflammation, just as it would if you had chronic inflammation on the back of your hand from a nervous habit that made you rub your hand constantly. A defense mechanism of the body is to instill pigment as a protective agent. Eventually the entire cornea may be blacked out, resulting in a total loss of vision.
Treatment usually takes the form of immune system modulating drugs applied topically to both eyes twice daily. There are two medications commonly used.
In people, it is common to use “punctal plugs,” tiny stoppers that prevent tears from exiting the eye through the lower puncta, or drainage hole in the eyelid. I inquired of Dr. Laurence Galle, ACVO, board-certified veterinary ophthalmologist why they are not used in dogs. “There’s really no ‘contraindication’ for them, they just aren’t really applicable to dogs as they are for humans. Most human “Dry Eye” is not nearly as severe as most of our KCS patients. You’ve got to have some tear production for punctal plugs to be effective. Most [KCS] dogs have very little tear production. Combine this with the expense of application, their need for reapplication (each with sedation or anesthesia), etc. and they just aren’t very marketable. Thus, no company has really tried to research the sizes, materials, etc. for punctal plugs in dogs.”
KCS is a condition with a good prognosis in most cases, although it requires regular followup visits to your pet’s doctor, slightly expensive medication and twice-daily therapy for life. Turn your back on this condition and your pet could lose his vision.
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