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Merck Manual

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Overview of the Eyelids and Tears


James Garrity

, MD, Mayo Clinic College of Medicine

Last full review/revision Jul 2020| Content last modified Jul 2020
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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.

Where Tears Come From

Where Tears Come From

An abnormality of the tear (lacrimal) glands can lead to insufficient tear volume or to an abnormality in the composition of the tears themselves. Without adequate tear volume or normal tear composition, the eyes can dry, be more vulnerable to irritation from vapors and airborne particles, and may be unable to normally fight infections. Abnormal tear production may be due to a problem within the tear glands and ducts (lacrimal excretory ducts, which carry tears into the eye) or due to a bodywide (systemic) disease that affects the tear glands, such as Sjögren syndrome.

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