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
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Tears are produced in the lacrimal glands, provide moisture to the eye, and are collected by ducts at the inner corner of the eye that drain into the nose.
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 Sjögren Syndrome Sjögren syndrome is a common autoimmune rheumatic disorder and is characterized by excessive dryness of the eyes, mouth, and other mucous membranes. White blood cells can infiltrate and... read more 
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An abnormality in the tear-drainage system (canaliculi, tear sac, or nasolacrimal duct) can interfere with drainage and cause excessive tearing or lead to inflammation and infection.
