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Dry eye can be caused by decreased tear production or increased tear evaporation. Normally, the eye constantly bathes itself in tears. By producing tears at a slow and steady rate, the eye stays moist and comfortable. Sometimes people do not produce enough tears or the appropriate quality of tears to keep their eyes healthy and comfortable. This condition is known as dry eye. The eye uses two different methods to produce tears. It can make tears at a slow, steady rate to maintain normal eye lubrication. It can also produce large quantities of tears in response to eye irritation or emotion. When a foreign body or dryness irritates the eye, or when a person cries, excessive tearing occurs.
What are the symptoms of dry eye?
The usual symptoms include:
Excess tearing from "dry eye" may sound illogical, but it can be understood as the eye's response to discomfort. If the tears responsible for maintaining lubrication do not keep the eye wet enough, the eye becomes irritated. Eye irritation prompts the gland that makes tears (called the lacrimal gland) to release a large volume of tears, overwhelming the tear drainage system. These excess tears then overflow from your eye.
When you blink, a film of tears spreads over the eye, making the surface of the eye smooth and clear. Without this tear film, good vision would not be possible.
The tear film consists of three layers:
Each layer has its own purpose. The oily layer, produced by the meibomian glands, forms the outermost surface of the tear film. Its main purpose is to smooth the tear surface and reduce evaporation of tears. The middle watery layer makes up most of what we ordinarily think of as tears. This layer, produced by the lacrimal gland, cleanses the eye and washes away foreign particles or irritants. The inner layer consists of mucus produced by the conjunctiva. Mucus allows the watery layer to spread evenly over the surface of the eye and helps the eye remain moist. Without mucus, tears would not stick to the eye.
Tear production normally decreases as we age. Although dry eye can occur in both men and women at any age, women are most often affected. This is especially true after menopause.
Dry eye can also be associated with other problems. For example, people with dry eyes, dry mouth, and arthritis are said to have Sjogren's syndrome. A wide variety of common medications, both prescription and over-the-counter, can cause dry eye by reducing tear secretion. Be sure to tell your doctor the names of all the medications you are taking, especially if you are using: