“I think Blinky has an eye infection, doc,” the owner says. Blinky is a shih tzu…or a Lhasa apso. I always get those mixed up. I push back the droopy bangs that flop across her face. Gooey green glop leaks from the corners of her eyes and there is crusty stuff all along the lid margins. Her conjunctiva is red and inflamed. I grab a small plastic bag containing two little white strips of special paper.
“This is a Schirmer Tear Test,” I tell Blinky’s mom. “To evaluate her tear production.” Folding down the tab at one end, I tuck the strip under the outer corner of Blinky’s lower lid and glance at the clock, hoping she will sit quietly for 60 seconds.
The Schirmer tear test is a simple but elegant diagnostic tool. The strip is made of a material like blotting paper, with very specific absorbency, marked off like a ruler in millimeters in indelible ink. At the top is a thin line of water-soluble blue dye. As Blinky’s eye waters, tears moisten the paper, picking up the blue dye which travels down the calibrated strip. At the end of 60 seconds, all I have to do is read where the blue dye has reached on the tiny ruler. A normal dog produces at least 15 millimeters of tears per minute. Blinky has made three.
Keratoconjunctivitis sicca, also known as KCS or “dry eye,” is the result of decreased production of the watery component of the tear film which is made primarily by glands found in the nicitans (third eyelid.) Tears function to nourish, lubricate, and protect the eye as well as remove debris and bacteria. Without adequate tears, Blinky’s eyes are constantly dry and irritated. Her body tries to compensate by producing more mucous (which is different from tears), creating that gooey, crusty situation. And her owner may be correct about that infection because secondary bacterial infections frequently ensue.
KCS is a relatively common disorder in dogs, though much rarer in cats. Breeds predisposed to it include cocker spaniel, West Highland white terrier, bulldog, shih tzu, Lhasa apso, bloodhound, Boston terrier, springer spaniel, Pekingese, pug, Samoyed, Yorkshire terrier, and cavalier King Charles Spaniel, to name just a few. These dogs are all prone to what is called immune-mediated lacrimal adenitis, or primary KCS, in which, for some unknown reason, the dog’s immune system starts attacking and destroying its own tear glands. This is the cause of the majority of KCS cases. Dry eye can also occur as a result of severe conjunctivitis or infections such as canine distemper virus. Sometimes dry eye can be a side effect of medications such as sulfa drugs or the NSAID analgesic etodolac. Luckily, medication-related cases often resolve if recognized promptly and the drug in question is discontinued.
What else can cause KCS? There is a condition dogs get called “cherry eye,” which is a prolapse of the gland of the third eyelid. It looks like a big red blob sticking out of the corner of the eye. Back when I was a student, we were taught to simply sedate the dog and snip it off. It took ten minutes and was an inexpensive procedure. The problem was we were also removing most of the tear glands. Breeds prone to cherry eye are also prone to KCS, but our surgery was substantially increasing the risk of dry eye later in life. It took a while for veterinarians to realize this connection, but nowadays we try to treat cherry eye with a procedure that keeps those glands intact. Things like trauma, radiation for cancer, and other surgeries can also cause KCS by affecting the nerves responsible for blinking or proper eyelid closure.
Blinky’s little strip of paper barely turned blue. With no history of surgery, drugs, or injury, this was probably immune-mediated KCS. “She’s going to need medication to stimulate tear production,” I explained. Topical cyclosporine helps her remaining glands to produce tears and is also anti-inflammatory. We usually start with a commercial veterinary ointment that is an 0.2% preparation twice daily. (Many owners may use a cyclosporine eye medication themselves because KCS occurs in people as well.) “It takes time to see results, “ I advised. “Let’s recheck her Schirmer tear test in a month.” If this didn’t work, we would have a compounding pharmacy prepare stronger eye drops of one or even two percent cyclosporine.
“Can’t I just use artificial tears?” Blinky’s mom asked.
“Sure,” I replied. “As long as you can put them in every two hours for the rest of her life.” The reality is that to provide adequate lubrication, artificial tears need to be applied very frequently. They can be useful as an ancillary treatment, especially in the early weeks, but are rarely a reasonable long-term solution. They also often contain preservatives that may be irritating after a while. But before starting any medications, we had to check one more thing.
“Dogs with KCS are also prone to corneal ulcers,” I said. “I’m going to put a drop of fluorescein stain in her eye. It starts bright orange, and then turns day-glo green. Don’t worry. It washes off.” The surface of the cornea is normally impermeable to water. With KCS, the dry surface is easily damaged. If the cornea is abraded, water-soluble dyes such as fluorescein will make any ulcerated areas visible with its bright green color. Blinky’s corneas were fine. She went home with cyclosporine, an antibiotic ophthalmic ointment for secondary infection, and a recheck appointment in a month.
KCS is painful. Left untreated, it can lead to severe corneal damage. The eye may respond to the chronic irritation by producing a brown pigment that can eventually cover the entire surface, causing blindness. Medication can sometimes reverse the vision loss, but not always, and lifelong treatment is usually needed. It makes me appreciate how such simple things as tears can be so crucial for vision and a good quality of life.