Dry Eye Syndrome
Dry Eye Syndrome Overview
To help keep your eyes comfortable and your vision optimal, a normal, thin
film of tears coats your eyes. Three main layers make up this tear film:
- The innermost layer is the thinnest. It is a layer of mucin (or mucus). This
very thin layer of mucus is produced by the cells in the conjunctiva (the
clear skin that lines the eye). The mucus helps the overlying watery layer to
spread evenly over the eye.
- The middle (or aqueous) layer is the largest and the thickest. This layer is
essentially a very dilute saltwater solution. The lacrimal glands under the
upper lids and the accessory tear glands produce this watery layer. This layer's function is to keep the eye moist and comfortable, as well as to help flush out any dust, debris, or foreign objects that may get into the eye. Defects of the aqueous layer are the most common cause of dry eye syndrome, also referred to as keratoconjunctivitis
- The most superficial layer is a very thin layer of lipids (fats or oils). These lipids are produced by the meibomian glands and the glands of Zeis (oil glands in the eyelids). The main function of this lipid layer is to help decrease evaporation of the watery layer beneath it.
Dry eye syndrome (DES) is a common disorder of the tear film, affecting a significant percentage of the population, especially those older than 40 years
of age. The estimated number of people affected ranges from 25-30 million in the United States. Worldwide, the incidence rate closely parallels that of the United States. DES can affect any race and is more common in women than in men.
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