Lachrymal Liquid

The lachrymal liquid is a physiological liquid aqueous and salted which runs out on the external surface of the Cornée and of the Conjonctive of the eye.

Production and flow

It is produced permanently by the lachrymal Glandes and spreads in a uniform way on the former surface of the eye.
In normal weather, it runs out by the lachrymal Canal until the Nasal fossae where it is eliminated in the Air in the form of microscopic droplets during the process of Respiration.
But in certain cases (pathological, or more generally emotional) lachrymal secretion is too important and the natural ways are then saturated and do not evacuate any more excess of secretion. The nasal fossae cannot any more pulverize the surplus of liquid, it runs out of the Nez and the eye finishing its race on the Visage where it is, partly, retained by different the Poil S from the Peau.

Roles

The lachrymal liquid humidifies and protects the Cornée.
The roles of the lachrymal liquid are dominating for the good performance of the visual apparatus:

the lachrymal liquid protects the eye against the aggressions outsides:

Against the Bacteria by presence of Lysozyme and Lactotransferrine in relatively large quantity.
Against the chemical agents suspended in the air. Indeed, the toxic or dangerous agents for the cornea are initially diluted in the liquid then eliminated by its permanent renewal. On the other hand this protective system is deteriorated by the port of contact lenses which cause the opposite effect: the products Toxique S will tend to concentrate between the internal surface of the lens and the surface of the eye. It is thus advised to withdraw them in end-of-day, and it is imperative to remove them before going in a part containing of the toxic products birds to high concentration (Insecticide S for example)
Against the small foreign bodies and irritating like dust, the Acarien S… which are eliminated from the same manner.

the lachrymal liquid nourishes the cornea:

Indeed, as well as the Os, the cornea is not a simple mineral but an alive body composed of cells are renewed regularly. These cells need Oxygène (of dioxygene to be exact) to survive, but for practical reasons, the cornea is not equipped with a vascular system : because if the cornea were crossed of Veinule S and Artériole S, these last would block or disturb the field of vision.
Oxygen necessary is then brought directly aqueous Humor, lachrymal glands (during the development of the liquid) , of the Air and the surrounding vessels: the dioxygene of the air and the small vessels bordering the cornea will dissolve in the lachrymal liquid, in addition to oxygen already present during its development, and will feed the cells. Then the Carbon dioxide produces by the cells of the cornea will dissolve in its turn in the lachrymal liquid to be eliminated with expulsion from ce-dernier.
It is interesting to notice that in certain cases (like the direct exposure to the smoke of Cigarette), the carbon dioxide concentration of the air will be higher than the concentration of CO₂ of the lachrymal liquid. To mitigate this risk of cellular intoxication (by osmotic effect) of the cornea, the secretion of liquid will be stimulated, in the form of a whimpering, to dilute the concentration of CO₂ and to restore a physiological balance normal.
During the phase of Sleep, where the Paupière S of the eyes are generally closed, oxygen is brought only by lachrymal film, the blood-vessels bordering the cornea like those papering internal surface of the eyelids. To avoid a Anoxia cornea, it occurs a light stimulation of the lachrymal Glandes associated with a Vasodilatation of the surrounding vessels (one can observe these phenomena at the time of the alarm clock where it is said that the eyes are red ).

The lachrymal film brings also different the Nutriment S necessary to the cells from the cornea, its nutrients come from the blood from which it is worked out by lachrymal glands.

the lachrymal liquid allows a concentration of the incidental beams of light (from its index of Réfraction) , but its role is infinitely lower than those of the cornea and the aqueous Humor. This capacity takes real importance only at the time of an excessive whimpering, where it causes a bad visibility (turbid and deformations of the perceived image) .

Composition

The liquid lachrymal is produced by filtration Sang by cells excrétrices of lachrymal glands, however certain components of this liquid (as the lysozyme) are not present in blood and are synthesized directly by these glandes.
The composition of this liquid varies slightly according to the layers of the EC-last:

the surface layer is secreted by the glands of Meibomius located on the internal surface of the eyelid, this layer is mainly aqueous (composed of Eau) but contains greasy Substance in order to limit a too fast draining due to the natural evaporation of water.
the transition course is strongly aqueous, contains the various nutrients and allows the transport of oxygen and carbon dioxide. It is secreted by lachrymal glands known as additional .
the deep layer is a fine slightly viscous film, because containing proteins, similar to a Mucus which is distributed uniformly on the surface of the eye; its role is to control the regular of the intermediary layers and surface distribution. It is secreted by mucous glands and glandular cells of the Conjonctive.

Lastly, the lachrymal liquid secreted at the time of the whimpering, is primarily aqueous (nearly water 99%) . It contains, inter alia, of the Sodium chloride, the lysozyme and the lactotransferrines. It is secreted by lachrymal gland principal located behind higher edge of the orbit.

Associated pathologies

Dacryocystite : infection of lachrymal glands
Disease of Goujerot-Sjögren, and the
dry Syndrome, (disease with ocular dryness)
Syndrome of Mikulik,
bacterial or viral Conjonctivite S (infection of the lachrymal liquid)
allergic Conjonctivite (hypersecretion of liquid by irritation of conjunctive)
Kératite
Some fracture S of the facial Massif can block, during their consolidations, the lacrymo-nasal channel: thus there is a permanent surplus of lachrymal liquid on the surface of the eye and this one runs out permanently on the face.

See too

Tear

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