Dry eye occurs when the eye does not produce tears properly, or when the tears are not of the correct consistency and evaporate too quickly.
In addition, inflammation of the surface of the eye may occur along with dry eye. If left untreated, this condition can lead to pain, ulcers, or scars on the cornea, and some loss of vision. However, permanent loss of vision from dry eye is uncommon.
Dry eye can make it more difficult to perform some activities, such as using a computer or reading for an extended period of time, and it can decrease tolerance for dry environments, such as the air inside an airplane.
a. Tear gland / lacrimal gland,
b. Superior lacrimal punctum,
c. Superior lacrimal canal,
d. Tear sac / lacrimal sac,
e. Inferior lacrimal punctum,
f. Inferior lacrimal canal,
g. Nasolacrimal canal.
Traditionally, the tear film has been viewed as having three distinct layers:
1. an outermost lipid (oily) layer
2. an aqueous layer that makes up 90% of the tear film volume; and
3. a mucin layer that coats the corneal surface.
However, it is now recognized that rather than being three distinct layers, the tear film is actually a lipid boundary layer with aqueous phases incorporating differing concentrations of lipid and mucins throughout.
In addition, mucins in the tear film play a much more active role in maintaining tear film stability than was once thought.
Korb DR, Craig J, Doughty M, Guillon J, Smith G, Tomlinson A. The Tear Film: Structure, Function and Clinical Examination. BCLA, 2002.