The eyelids play a key role in protecting the eyes. They sweep debris away when the eyes are closed and help spread moisture in the form of tears over the surface of the eyes when they open. The eyelids provide a mechanical barrier against injury by closing quickly when needed.

Tears are produced by the main and accessory lacrimal glands (lacrimal glands) and collect in ducts in the inner corner of each eye. From there they drain into the nose. The main lacrimal gland is responsible for reflex tearing, which occurs, for example, when the eye is irritated by a foreign object or by cutting an onion. Accessory tear glands are responsible for keeping the eye well lubricated, comfortable and free of dust, all of which help with clear vision.

An abnormality in the 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 may dry out, be more vulnerable to irritation from vapors and airborne particles, and may be unable to normally fight infection. Abnormal tear production may be due to a problem in the lacrimal glands and ducts or due to a body-wide (systemic) disease affecting the lacrimal glands, such as Sjögren’s syndrome.

An abnormality in the tear drainage system (canaliculi, lacrimal sacs, or nasolacrimal ducts) can interfere with drainage and cause excessive tearing or lead to inflammation and infection.