The tear film is a thin protective layer that coats the surface of the eyeball and is mechanically spread over it by constantly blinking without thinking. What is the composition of the tear film? What is his role? What happens when tear film disturbance occurs?

Contents:

  1. Tear film - layers
  2. Tear film - composition
  3. Tear film - Features
  4. Tear film disorder
  5. Tear film - treatment

For thetear filmto be properly distributed over the entire surface of the eye and to have a protective effect, three conditions must be met. The first is the correct blink reflex, the second is the close contact between the outer surface of the eye and the eyelids, and the third is the correct structure of the corneal epithelium.

Tear film - layers

A correct tear film consists of three layers:

  • watery, secreted by the lacrimal glands
  • of mucus secreted by conjunctival goblet cells
  • fat secreted by Meibom's sebaceous glands

Each of these layers plays a very important role not only in protecting the eyeball, but also in the process of proper vision.

The fatty (lipid) layer is the outer layer of the tear film. It prevents the evaporation of tears, maintains the stability of the tear film and allows the eyes to move freely (without resistance).

The thickness of the lipid layer increases with increased blinking and decreases with rarely blinking. The deficiency of this layer contributes to the discomfort of dry eye.

The water layer is the middle part of the tear film. It consists mainly of water, electrolytes, mucin and protein. Its main task is to properly moisturize the corneal epithelium and supply it with oxygen.

This layer contains, among others, immunoglobulins A and thus has antibacterial properties, and thus affects the disinfection of the eye surface.

The water layer of the tear film removes all impurities from the eye surface and maintains a smooth optical surface by eliminating minor irregularities of the anterior surface of the cornea.

The mucus (mucin) layer allows the tear film to adhere tightly and stay on the surface of the cornea. Deficiencies in the mucosa may result from a lack of waterand excessive evaporation of tears.

Tear film - composition

The tear film must be properly composed and produced in the right amount for the eyes to be properly nourished and kept in good condition. Abnormalities in any of the three previously mentioned layers lead to a condition known as dry eye syndrome.

Tears is a transparent liquid with water as the main ingredient. In addition to it, the component of tears is also:

  • sodium chloride (about 0.9%) giving them a s alty taste
  • proteins (about 0.5-0.7%) - albumin, lysozyme (dissolves the cell membrane of bacteria) and globulins
  • ascorbic acid
  • sugar and urea
  • electrolytes (chloride and phosphorus anions, sodium and potassium cations)

Tear film - Features

The most important role of the tear film is to moisturize and nourish the surface of the eye, preventing corneal damage. The tear film acts as a "lubricant" that helps the eyelids move freely. Chemical substances in tears have antibacterial, antiviral and antifungal properties, protecting the eye from infections.

The tear film also affects the regulation of visual acuity. The surface of the tear film in contact with the outside world (air) has the greatest power to refract light rays in the entire optical system of the eye. It is about 60 diopters.

The tear film focuses light rays on the retina, which contributes to sharp vision. Therefore, even slight disturbances in the continuity of the tear film may have an impact on the deterioration of visual acuity.

Tear film disorder

The most common cause of the tear film malfunction is disturbance in the composition of the water layer. Reducing the production of tears is most often associated with the autoimmune process of atrophy of the tear glands that occurs in the elderly.

Common causes include taking certain medications, such as alpha and beta-blockers used in the treatment of high blood pressure, antidepressants, antiarrhythmic drugs, anti-Parkinson drugs, antihistamines or drugs used to treat peptic ulcer disease.

This group also includes topical eye medications that reduce eyeball congestion. Gland damage is less commonly caused by connective tissue diseases, sarcoidosis, congenital lacrimal gland syndromes, or orbital tumors.

Disturbances in the composition of the water layer of the tear film may also occur in people who wear contact lenses or have undergone laser vision correction. In these cases, the cause of reduced tear secretionthere is damage to the corneal sensation, which stimulates the secretion of tears by reflex.

Disorders in the mucous layer result from the reduction of the amount of mucin in the tear film, with the proper secretion of the tear fluid. This causes the tear film to become unstable and break very quickly. This type of disorder is most often caused by vitamin A deficiency, which causes damage to the goblet cells.

Diseases that impair mucin secretion by destroying goblet cells are:

  • trachoma
  • Stevens-Johnson syndrome
  • chronic conjunctivitis
  • erythema multiforme
  • chemical and thermal damage

Disturbances in the fat layer are most often associated with improper functioning of the meibomian glands. A common cause is chronic inflammation of the eyelid margins or the glands themselves, caused by a bacterial infection.

Lipase enzymes secreted by bacteria break down lipids, which increases the amount of fatty acids that can disrupt the tear film and toxically damage the corneal epithelium. Excessive lipids can cause tears to foam.

Tear film - treatment

The causal treatment of tear film disorders is often difficult, therefore symptomatic treatment is most often used. When the water layer of the tear film is disturbed, moisturizing eye drops called artificial tears are used to moisturize the surface of the eye.

These preparations mainly consist of water with the addition of a substance increasing the viscosity of the liquid. It is best to choose preparations that do not contain preservatives. In the case of disorders of the fat layer, a liposomal spray can be used.

It improves the hydration of the surface of the eyelids and eyes, and also stabilizes the lipid layer of the tear film. It is very easy to use, you can spray it on your closed eyelids from a distance of about 10 centimeters.

Then, with a few blinks, the preparation is spread over the surface of the eye. Liposomal spray should be used 3-4 times a day.

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About the authorAnna Jarosz A journalist who has been involved in popularizing he alth education for over 40 years. Winner of many competitions for journalists dealing with medicine and he alth. She received, among others The "Golden OTIS" Trust Award in the "Media and He alth" category, St. Kamil awarded on the occasion of the World Day of the Sick,twice "Crystal Pen" in a nationwide competition for journalists promoting he alth and many awards and distinctions in competitions for the "Medical Journalist of the Year" organized by the Polish Association of Journalists for He alth.

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Category:

Eye diseases and vision disorders