What is dry eye?

Dry eye is a catch-all term for what happens to people when one or more things go wrong with the tear layer (tear film) on your eyes. A healthy tear film nourishes and protects your sensitive surface tissues and is also an important part of providing clear vision. An unhealthy tear film can cause many different kinds and degress of discomfort or pain and can interfere with good vision.

Unfortunately we are stuck with this silly term "dry eye", which is both inaccurate and misleading. First, it's usually inaccurate as most people with "dry eye" don't actually have dry eyes (in fact many have chronically watery eyes... Click here for more about dry eye symptoms.). Second, it sounds quite trivial to anyone not "in the know". There have been attempts - mostly unsuccessful - to come up with a better, more descriptive names, the best known of which is DTS (dysfunctional tear syndrome). But it's difficult to make something like that stick. Many doctors use the terms chronic dry eye, dry eye syndrome, or dry eye disease.

If you have been told by a doctor that you have dry eye, but have been given no further specifics, you have not been adequately diagnosed. It's like a cardiologist telling you that you have heart trouble. You need to know more. Please read this article for more information.

The human tear film is complex, as is the system that produces it and spreads it around. The tears consist mostly of an aqueous (watery) layer produced by the lacimal glands but then it is sealed in with a thin lipid (oily) layer on top, produced by the meibomian glands to stand between your tears and the air so as to keep your tears from evaporating too quickly. Between the tears and your eye surface itself is a thin mucous (sticky) layer produced by cells in the eye surface to help tears adhere properly to the surface of the eye. Then there are the eyelids, which play a role in both producing and pumping out the oil layer of the tears and in constantly spreading tears over your eyes, so anything going wrong with either the glands in the lids or in the mechanics of the lid function (such as incomplete lid closure or poor or infrequent blinking) will also affect the tear film.

Disruptions to any one part of this system - whether a surgery that changes how your eyelids close or cuts nerves in the cornea, or a hormonal change affecting any of the glands' output, or a dermatological condition affecting the eyelids in unseen ways, or poor nutrition, or constant exposure to very dry air or wind, or a drug that has side effects impacting mucous production in the body, or any other of a myriad of possible factors - may cause one of the conditions that fall into the "dry eye" bucket.