Dry Eye is what happens when the immune system attacks and shuts down the dog’s own tear gland. The tear covering on the eye is supposed to be made of 2 distinct layers: a liquid, saline layer that is produced by the tear glands; and a mucus layer, produced by mucus glands, that floats on top like an oil slick on water.
When the saline layer is not there, the mucus glands go into overdrive, trying to keep the eye lubricated all on their own. Without the saline layer for the mucus to float on, though, even loads and loads of mucus can not get good coverage of the eye. The tissues of the eye dry out, and get damaged by microscopic cracks. This is where the medical name for Dry Eye comes from: KCS stands for Keratoconjunctivitis Sicca (kerato- means cornea, conjuntiva means the membranes lining the eye and socket, -itis means inflammation, and sicca means dry).
Bacteria find these damaged tissues and thrive – a treatment with an antibiotic ointment will often improve Dry Eye, both because the antibiotic takes down the bacteria and because the ointment itself provides some lubrication. But as soon as you stop the ointment, you are back to square one: you have not actually treated the Dry Eye. This relapse is one of the clues to say that the eye has an underlying condition, such as Dry Eye.
The other clue is a test we do to measure tear production, called a Schirmer Tear Test (STT). A paper strip is held up against the moist tissues of the eye, and kept in place for 60 seconds. We measure how far the tears have moistened the strip in that 60 seconds. Anything over 15 mm is technically normal; however, if the eye is super-irritated, where I expect it to be tearing like crazy, and the strip only reaches 15 mm, I may still consider that to be abnormal as the tear response is not appropriate to the state of the eye. Most very inflamed eyes should produce a tear strip in the upper 20’s.
Over time, cells that are trying to fix the damaged cornea migrate across it, producing a dark patch over the clear window of the eye and obscuring vision. This patch may shrink up a bit with treatment, but it never goes away completely. If the eye gets to this stage, vision is permanently impaired.
The treatment for Dry Eye involves the same drugs used in preventing organ transplant rejection; after all, we are just trying to get the body’s immune system to stop rejecting its own tear gland. The most common of these drugs is called Cyclosporin, and comes in an ointment called Optimmune. At the start, when the immune attack on the tear gland is in full swing, the ointment needs to be given twice a day. The medication is not cheap, so it is important to learn how to put ointment into the eye efficiently – otherwise, the dog moves at the wrong time and half the tube of medication winds up down on his cheek! As the eye starts to respond, the frequency of dosing can be dropped down. You may even get to a point where you can stop for a while, but watch the eye! The condition is not cured, it is just in remission and can come back. Routine tear strip monitoring can help keep track of how the eye’s tear production is doing.