Eyelids and tears work together to protect the eye against damage. The eyelids act as shutters, closing to stop material from entering the eyes. Tears keep the surface of the eyes moist and help to prevent infection. Disorders of the eyelids or tear system can damage the eyes, but most are easily treated if detected early.
The upper and lower eyelids provide essential protection for the eyes. If anything approaches the eye or face rapidly, the eyelids close together almost instantaneously as a reflex action. Furthermore, each eyelid has two or three rows of eyelashes, which help to prevent small particles from entering the eye.
Tears are another important part of the eyes’ defences. They are made up of a salty fluid produced by the lacrimal (tear) glands, which are located above the upper eyelids. Tears lubricate the exposed surface of the eye and wash away potentially harmful materials, such as dust and chemicals. Tears also contain a natural antiseptic that helps to protect the eye against infection.
The initial articles in this section focus on conditions that affect the eyelids. These conditions include infections of the eyelid and disorders that alter the physical shape of the eyelids. The section then discusses disorders that affect the tear system, which include blockage of the tear drainage channels and problems with tear production. Disorders that affect the physical structures of the eye itself are covered elsewhere in the guide (see Eye disorders).
For more information on the structure and function of the eye, see Eyes and Vision.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.