Dry eyes are caused by a lack of adequate tears or abnormal composition of tears. Your tears are a complex mixture of three basic layers oil, water, and mucus. This mixture helps make the surface of your eyes smooth and clear, and helps protect your eyes from infection. Problems with any of these layers can cause dry eye syndrome.
The outer layer (oil layer) is produced by the meibomian glands that line the edge of the upper and lower eyelids. The water layer is produced by the lacrimal gland located under the orbital rim bone just below the eyebrow. The mucus layer is produced by microscopic goblet cells in the conjunctiva.
Illustration: The eye and tear production
For some people, the cause of dry eyes may be due to an imbalance in the composition of their tears, or they do not produce enough tears to keep their eyes comfortably lubricated. Age, eyelid problems, certain ocular and systemic diseases and medications, and other causes such as environmental factors and hormonal changes can also lead to dry eyes.
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