Tears are the liquid product of a process of
lacrimation to clean and lubricate the eyes.
 In human, the tear film coating the eye, known
as the pre-corneal film, has three distinct
layers, from the most outer surface:
1. The lipid layer contains oils secreted by the
meibomian glands (or tarsal glands). The outermost layer of the tear film coats the aqueous
layer to provide a hydrophobic barrier that
retards evaporation and prevents tears spilling
onto the cheek
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2. The aqueous layer contains water and other
substances such as proteins (e.g. tear lipocalin,
lactoferrin, lysozyme and lacritin) secreted by
the lacrimal gland. The aqueous layer serves to
promote spreading of the tear film, control of
infectious agents and osmotic regulation
3. The mucous layer contains mucin secreted by
the conjunctival goblet cells. The inner-most
layer of the tear film, it coats the cornea to
provide a hydrophilic layer that allows for
even distribution of the tear film, as well as
mucus covering of the cornea.
• The tear gland of the eye of humans and
other vertebrates. It lies beneath the upper
eyelid.
• The lachrymal gland is controlled by the
autonomic nervous system. It continuously
secretes small amounts of sterile, slightly
antiseptic, tears which keep the cornea
moist.
• Tears drain away through two small
openings (puncta) at the inner corner of the
eye into the lacrimal caniculi. From there
the tears pass into the nasal cavity via the
lacrimal sac and nasolacrimal duct, or
tear duct.
1. Basal tears: In healthy mammalian eyes, the cornea
is continually kept wet and nourished by basal
tears. They lubricate the eye, and help to keep it
clear of dust. Tear fluid contains water, mucin,
lipids, lysozyme, lactoferrin, lipocalin, lacritin,
immunoglobulins, glucose, urea, sodium, and
potassium. Some of the substances in lacrimal fluid
(such as lysozyme) fight against bacterial infection
as a part of the immune system.
It is a typical body fluid with a salt content similar
to blood plasma. Usually, in a 24-hour period, 0.75
to 1.1 grams of tears are secreted, this rate slows
with age.
2. Reflex tears: The second type of tears results
from irritation of the eye by foreign particles,
or from the presence of irritant substances such
as onion vapors, tear gas or pepper spray in the
eye's environment. It can also occur with bright
light and hot or peppery stimuli to the tongue
and mouth. It is also linked with vomiting.
These reflex tears attempt to wash out irritants that
may have come into contact with the eye.
3. Crying or weeping (psychic tears): The third
category, generally referred to as crying or
weeping, is increased lacrymation due to strong
emotional stress, suffering or physical pain.
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Emotional tears contain more of the proteinbased hormones prolactin, adrenocorticotropic
hormone, and leucine enkephalin (a natural
painkiller) than basal or reflex tears
• Water
• Electrolytes, the electrolytes are principally Na+, K+,
Cl-, and HCO-, with lower levels of Mg2+ and Ca2+
•Proteins – secreted from the lacrimal gland,
(lysozyme, lactoferrin, lipocalin, and sIgA).
• Lipids - from the meibomian glands
•Mucins
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lysozyme (an enzyme capable of destroying the cell
walls of certain bacteria and thereby acting as a mild
antiseptic).
Lactoferrinan (an iron-binding protein , by
combining with iron, lactoferrin prevents
microorganisms from combining with and using
iron for their growth).
The levels of the major tear proteins are known to
decline with age at the same time the volume of
tears also tends to decline leading to a dryer eye
parallel to aging.
1) Tears act as both a delivery and an excretory route
for nutrients and metabolic products of the corneal
epithelium.
2) The presence of the tear film improves the quality of
the retinal image by smoothing out irregularities of
the cellular surfaces.
3) It acts as a lubricant preventing eye dryness which
is provided by the tear film coating the cornea.
4) It plays a protective role against infection carried out
mainly by its protein content of lysozymal enzymes,
lactoferrin, secretory IgA
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"Crocodile tears syndrome” : Shedding tears
while eating
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Keratoconjunctivitis , more commonly known
as dry eye, is a very common disorder of the
tear film
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Pain
Light sensitivity
A gritty sensation
A feeling of a foreign body or sand in the eye
Itching
Redness
Blurring of vision