Tear . It is a liquid produced by the body’s lacrimation process to clean and lubricate the eye . They are mainly involved in ocular optics and in the normal operation of the eyeball and its structures. Any alteration of the tear influences visual acuity .
The lacrimal gland is the main secretor of the tear.
[ hide ]
- 1 Path of the tear
- 2 Tear film
- 3 Composition of the tear
- 4 Amount of discharge
- 5 Tear function
- 1 Main
- 6 =
- 1 Sources
The path of the tear is divided into two parts:
- Secretion: The secretion of the lacrimal gland is carried out by means of two parts communicated in it: the upper part (or orbital portion) and the lower part (or eyelid portion). The tear passes through ducts or canaliculi that drain to the bottom of the upper sac, also known as the fornix of the conjunctiva . Once in the cornea , the tear spreads on the inner face of the eyelid , supplying it with oxygen and nutrients .
- Sewer system. In the drainage system, the tear enters through two points and upper and lower tear holes, those through which the tear passes to the tear ducts that join the caruncle. After this, the tear drains into a cavity called the lacrimal sac, and from this it passes to the tear-nasal canal that will drain to the inferior meatus of the nostril , in the nose. This is why when we cry, we run our own tears.
The tear film consists of 3 layers (from the outermost to the innermost):
- Lipid layer: made up of fats. Product of the secretion of the Meibomian Glands . It causes Tear Evaporation to take place slowly and decrease the evaporation force.
- Aqueous layer: formed by water. Product of the secretion of the main glands. Administers enough oxygen for corneal metabolism .
- Mucous layer: formed by mucin (mucus). Product of the secretion of the conjunctival glands ( goblet cells and Henle’s Crypts ). The adhesiveness of the mucin prolongs the residence time of the tear on the ocular surface, delaying its elimination by eyelid scanning. It also makes the corneal surface, especially, smooth, and the flaking irregularities of the epithelium are eliminated.
- Water (98.3%).
- Great content in Glucose . In pathological conditions the proportion is similar to that of blood plasma.
- Proteins : Albumin , Globulin and Lysozyme (which has antimicrobial capacity). The amount of protein decreases before inflammation, continuous tearing, etc.
- Sodium and Potassium .
Amount of discharge
- First 24 hours: There is already a tear discharge, except in certain premature babies.
- 25 years: Tear production begins to decrease.
- 50 years: Limit between production and needs.
- 75 years: All people suffer from age-old dry eye.
Production is higher in men than in women. In addition, in women it decreases at different times of the menstrual cycle .
- Metabolic: Corneal metabolism is carried exclusively through oxygen that comes exclusively from the water layer. So blinking constantly distributes oxygen. Sometimes oxygen gets bad in contact lenses wearers .
- Optic: The tear is attached as a lens that together with the anterior aspect of the cornea form a surface of around 48 diopters. Optical function is altered by altering the tear film.
- Bacteriostatic: For lysozyme and Gammaglobulin of which it consists, which alters and breaks the walls of bacteria.
- Lubricant: Prevents desiccation of the cornea.
- Photoabsorbent: Absorbs part of the ultraviolet rays from sunlight.
- Nasal wetting: When the lacrimal sac is removed, nasal dryness is caused.
- Protective: Drag small debris and foreign bodies with the blink.