Kyynelten

Kyynelten are the watery secretions produced by the lacrimal system, most familiar as tears. They play a protective and signaling role for the eye, helping to keep the corneal surface moist, removing irritants, and contributing to immune defense.

Anatomy and tear film

Tear production occurs mainly in the lacrimal glands, with additional contribution from accessory glands. The tear film that coats the ocular surface consists of three layers: a superficial lipid layer produced by the Meibomian glands, an aqueous layer from the lacrimal glands, and a mucin-containing layer from goblet cells in the conjunctiva. Blinking spreads the tear film and maintains coating of the cornea and conjunctiva. Tears drain primarily through tiny puncta at the inner corners of the eyelids, into canaliculi, then the nasolacrimal duct, and finally into the nasal cavity.

Types and functions

There are three recognized types of tears. Basal tears are produced continually to keep the eye moist and nourished. Reflex tears arise in response to irritants such as wind, smoke, or foreign bodies. Emotional tears are produced in response to strong feelings and may differ in composition and quantity from reflex tears. Tears provide lubrication, deliver oxygen and nutrients to the avascular cornea, wash away debris, and contain enzymes and antibodies that help protect against infection.

Composition and health considerations

Tear composition includes water, electrolytes, proteins (such as lysozyme and lactoferrin), lipids, mucins, and immunoglobulins. Disruptions in tear production or drainage can cause conditions such as dry eye (keratoconjunctivitis sicca) or epiphora (excessive tearing). Treatments range from artificial tears and anti-inflammatory therapies to addressing underlying lacrimal drainage problems.

Etymology

In Finnish, kyynelten is the genitive plural form of kyynel, meaning tears, used when referring to tears belonging to or associated with something.