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Tears are a liquid process of lacrimation to clean and lubricate the eyes. The word lacrimation may also be used in a medical or literary sense to refer to crying. Strong emotions, such as sorrow or elation, may lead to crying. Although most land mammals have a lacrimation system to keep their eyes wet, Humans are the only animal generally accepted to cry emotional tears. 
Additional recommended knowledge
In humans, the tear film coating the eye has three distinct layers, from the most outer surface:
Having a thin tear film may prevent you from wearing contact lenses as the amount of oxygen need is higher than normal and contact lenses stop oxygen entering your eye. You will find that your eyes will dry out while wearing contact lenses whilst having a thin tear film. Special eye drops are available for contact lense wearers, also certain types of contact lenses are designed to let more oxygen through.
Drainage of tear film
One lacrimal gland is located superiortemporally to each eye, behind the upper eyelid. The lacrimal glands secrete lacrimal fluid which flows through the main excretory ducts into the space between the eyeball and lids. When the eyes blink the lacrimal fluid is spread across the surface of the eye. Lacrimal fluid gathers in the lacrimal lake, and is drawn into the puncta by capillary action, then flows through the lacrimal canaliculi at the inner corner of the eyelids through the nasolacrimal duct, and finally into the nasal cavity. An excess of tears, as with strong emotion, can thus cause the nose to run. 
Types of tears
There are three very basic types of tears:
Diseases and disorders
Quality of vision is affected by the stability of the tear film.
Keratoconjunctivitis sicca, more commonly known as dry eye, is a very common disorder of the tear film. Paradoxically, sufferers can experience watering of the eyes which is in fact a response to irritation caused by the original tear film deficiency.
"Leamy Eye" is a condition whereby there is excessive watering of one eye, seemingly for no apparent reason, in response to environmental stimuli.
Most mammals will produce tears in response to extreme pain or other stimuli, but crying as an emotional reaction is considered by many to be a uniquely human phenomenon, possibly due to humans' advanced self-awareness. Some studies suggest that elephants and gorillas may cry as well.
In nearly all cultures, crying is seen as a specific act associated with tears trickling down the cheeks and accompanied by characteristic sobbing sounds. Emotional triggers are most often anger and grief, but crying can also be triggered by sadness, joy, fear, laughter or humor, frustration, or other strongly-experienced emotions.
In many cultures, crying is associated with babies and children. Some cultures consider crying to be undignified and infantile, casting aspersions on those who cry publicly, except if it is due to the death of a close friend or relative. In most cultures, it is more socially acceptable for women to cry than men, although this is rapidly changing in a more equal society.
Some modern therapy movements such as Re-evaluation Counseling believe that crying is beneficial to health and mental wellbeing, and positively encourage it.
An insincere display of grief or dishonest remorse is called crocodile tears, from the ancient anecdote that crocodiles would pretend to weep while luring or devouring their prey.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tears". A list of authors is available in Wikipedia.