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The term dry-eye syndrome (DES) refers to a number of different conditions, all of which are characterized by inadequate lubrication of the surface of the eye.
Usually inadequate lubrication is caused by a deficiency of one or more of the tear-film layers (there are three of them: the aqueous, the mucin and the lipid layer). There are two glands involved the production and regulation of tears. The lacrimal gland is responsible for tear production and the meibomian gland is responsible for the stability of the tear film. If these glands are are not working properly, the eyes dry out.
Surprisingly, dry eye syndrome can also lead to excessively watery eyes due to tears lacking the proper balance of mucous, water, and oil to coat the eyes properly. Chronic dry eye can lead to damage of the eye’s surface, an increased risk of eye infections, and eventually, the inability to produce tears. Left untreated, severe forms of dry eye can even damage your vision.
Dry-eye can be caused by certain drugs, eyelid problems or defects in the epithelial cell's of the cornea (the clear surface of the eye) that are caused by infection or trauma. Dry eye can also be associated with systemic diseases such as Sjögren's syndrome.
Sometimes the defects in the epithelial cells of the cornea that cause dry eye are a side effect of LASIK surgery. Dry eyes are extremely common after LASIK. It is thought that LASIK damages the nerves in the cornea making it difficult for them to tell the brain that its time to produce more tears.
The symptoms of dry eye vary from patient to patient. Most patients have mild to moderate symptoms, including eye discomfort, the feeling that there is something in their eye, burning, stinging, grittiness, light sensitivity, blurring, tired eyes (visual fatigue) and the inability to continue to wear contact lenses. In some patients, symptoms are debilitating.
Dry eye syndrome is one of the main reasons that patients visit eye doctors in North America.
It is difficult to determine the prevalence of dry eye syndrome because different studies use different criteria for diagnosing the syndrome. Determining the prevalence of DES is complicated by the lack of a gold standard for diagnosis; moreover, each study seems to use different criteria.
Based on a number of different studies, the prevalence of dry eye syndrome is anywhere from 6.7 percent to 28.7 percent. Women are 1.5 to three times more likely than men to have the dry eye syndrome. The group that is most at risk of dry eye disease is postmenopausal women and women with premature ovarian failure. There is also an increased risk of dry eye syndrome in pregnant and lactating women.