Introduction
The eyelids play a key role in protecting the eyes. They sweep away debris when the eyes close and help spread moisture (tears) over the surface of the eyes when they open. The eyelids provide a mechanical barrier against injury by closing rapidly when needed.
 See the figure Viewing the Lacrimal Structures.
An abnormality of the tear (lacrimal) glands can lead to insufficient tear production or to a deficiency in the composition of the tears themselves. Without adequate or normal tear production, the eyes can dry and may be unable to normally fight infections from airborne particles, fingertips, or surrounding skin. Abnormal tear production may be due to a problem within the tear glands (lacrimal glands) and ducts (lacrimal excretory ducts, which carry tears into the eye) or due to a systemic disease that affects the tear glands, such as Sjögren's syndrome (see Section 5, Chapter 68).
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