Article Medically Reviewed By:
Robert A. Latkany, M.D.
Physician Eyecare of NY New York, NY
Overview
What Is It?
Dry eye syndrome is a group of disorders in which either you don't produce enough tears, or you have unstable tears or excessive tear evaporation. Tears keep your eyes moist, lubricate the surface of the eye for eyelid closure and guard against infection. They also wash away allergens and protect the eye. Without tears, good vision is impossible. Dry eye syndrome is a group of disorders affecting the film of tears over the eye. When you have dry eye syndrome, either you don't produce enough tears, or you have unstable tears or excessive tear evaporation. In the United States, nearly five million people age 50 or older have dry eye syndrome. Of these, more than three million are women and more than one and a half million are men. In addition, tens of millions of Americans experience less severe symptoms of dry eye.
Understanding the Role of Tear Film
The tear film on your eyes actually consists of the following three major components:
- Lipid. The outer layer of the tear film is covered by an oily layer produced by meibomian glands in the lower and upper eyelids. This layer smoothes the eye's surface and keeps tears from evaporating too fast and helps them stay on the eye.
- Aqueous. The aqueous component is a watery layer that is produced by the lacrimal glands. This layer makes up most of what we normally consider tears. It nourishes the cornea (the clear tissue of the outer protective layer of the eye that transmits light) and the conjunctiva (a thin, clear layer of tissue that covers the white outer surface of the eye). This tear layer also cleanses the eye and washes away foreign particles or irritants that are wrapped up by the other major component—mucin.
- Mucin. The goblet cells of the conjunctiva, as well as the surface cells of the cornea and the conjunctiva, produce this protective lubricant of tears. It helps spread the watery layer of tears across the eye to keep the eye wet, and it traps and wraps up foreign pathogens and debris so they do not damage the ocular surface
Characteristics of Dry Eye Syndrome
Dry eye syndrome is one of the most common reasons people visit an eye health professional. It occurs most often in the elderly; as we age, the eyes naturally produce fewer tears. However, sometimes, the lipid and mucin layers produced by the eye are so unstable that tears can't remain on the eye long enough to keep it lubricated. Consequently, some people with dry eye may actually have tears running down their cheeks! Dry eye syndrome, also called keratoconjunctivitis sicca or dysfunctional tear syndrome, is the result. In some people, dry eyes result from an imbalance in the composition of their tears or an inability to produce enough tears to keep their eyes sufficiently lubricated. In addition, eyelid problems, environmental factors, certain medications and other causes can lead to d...
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