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Structure of the tear film
Anyone who thinks our tears are simply water underestimates the sophisticated protective function of the eyes. This is because the tear film consists of several layers, and each of them performs an important task in moisturising and protecting the surface of the eye.
What role does the tear film play?
The tear film functions like a protective shield for the surface of the eye. But often we don’t notice tears until we are crying with joy or sadness – or cutting onions. At the same time, the tear film has important tasks in terms of moisturising, cleaning and protecting the eyes with every blink:
- An intact tear film protects the cornea and conjunctiva from drying out and keeps them smooth.
- It supplies the cornea with nutrients and oxygen, as it has no blood vessels of its own.
- Foreign bodies are removed and rinsed out of the eye.
- The tear fluid has antibacterial properties and can fend off pathogens.
- In addition, wetting the eye improves vision because the tear film compensates for small irregularities in the cornea and ensures optimal refraction of the incident light.
Hence, without the tear film, we would not be able to see clearly, we would constantly have inflammation of the eye, we would have to permanently struggle with burning, sore eyes and remove small foreign bodies from the surface ourselves. All good reasons to pay a little more attention to the tear film.
Vladimir Voronin - stock.adobe.com
InfographicThe tear film
How many layers does the tear film have?
A healthy tear film consists of three layers: a mucous layer, an aqueous layer and an oily layer, which together form a perfect protective system for our corneal surface. Each of the three layers has a specific function:
- Mucin layer: The inner layer lies directly on the surface of the eye and consists of mucous substances called mucins. These are formed in the goblet cells of the conjunctiva. It evens out irregularities on the surface of the eye and ensures that the tear film adheres to its surface in the first place.
- Aqueous layer: The middle layer is the main component of the tear film and consists mainly of water. It provides moisture and nourishment, but also contains two important proteins for immune defence: lysozyme and lactoferrin. They ensure that invading bacteria are rendered harmless and protect against infections. The aqueous layer is formed in the lacrimal gland.
- Lipid layer: The outer layer is a thin, oily film that covers the aqueous layer, stabilises it and protects it from evaporation. The oily secretion is produced in the sebaceous glands located in the upper and lower eyelid margin, called the meibomian glands. When blinking, the lipid film spreads evenly over the surface of the eye and protects the tear film from premature tearing.
What is the composition of the tear fluid?
Aside from water, the tear fluid also contains other components:
- hyaluronic acid
- proteins
- antibodies
- salt
- glucose
- antibacterial enzymes
- oxygen
- other nutrients
What we perceive as salty tears is actually a very complex system, the interaction of which protects, nourishes and keeps our most important sensory organ functioning day and night.
Dry eyes: When the tear film tears up too quickly
More and more people suffer from dry, red and itchy eyes. Then it may be that the tear film breaks down too quickly and no longer protects the surface of the eye sufficiently.
On the one hand, this is due to the fact that in modern everyday life we stare at screens for a very long time and thus blink less. Smartphone, tablet, PC, TV - work and leisure time are no longer imaginable without these devices.
However, they mean stress for the eyes, because the concentrated gaze on the screen reduces the frequency of eyelash blinks and the surface of the eye is less frequently wetted with tear fluid. Environmental influences such as wind, smoke or dry heating air also cause the tear fluid to evaporate more quickly.
On the other hand, sebum production in the eyelid margin glands may be disturbed, for example by meibomian gland dysfunction. If too little sebum is produced in the glands or there is a buildup of secretions in the gland ducts, then the fat content of the tear film is too low. This causes the protective lipid layer to tear prematurely and can lead to dry, irritated, itchy or burning eyes. Incidentally, watery eyes can also be a symptom of inadequate secretion production, because without the stabilizing lipid layer, the watery tears simply flow out of the eye.
How can I support the tear film?
An intact tear film is extremely important for eye health and should be actively supported in its important function. Here are a few tips:
- Blink more frequently so that the surface of the eye is regularly wetted with the tear film.
- Eating a healthy diet with vitamins, omega-3 and omega-6 fatty acids.
- Drinking enough fluids keeps the eyes hydrated and protects them from drying out.
- Daily eyelid margin hygiene removes dirt and debris from the eyelid margins and prevents inflammation.
- Exposure of the eyelids to heat promotes blood circulation and stimulates the production of sebaceous glands.
In the case of dry eyes, the regular use of moisturizing or wetting eye drops during the day is also recommended, as well as eye ointments for the night, depending on the severity. Regular eyelid hygiene can be supported with the use of eyelid hygiene wipes or an eye spray.