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What should you know about the exterior of the eye and the tear film?

The ocular surface (clear cornea and white conjunctiva) is permanently covered by a thin liquid layer, the tear film. This is very important for the health and visual performance of the eye.

The tear film is composed of three merging layers, the lipid layer, the aqueous layer and the mucin layer.

Exterior eye schematics

When a person blinks, the tear film is evenly distributed over the ocular surface by the ‘windshield wiper’ of the eye, the eyelids, to keep the surface moist and to smoothen the corneal surface contributing to optimized vision.

The lipid or fatty layer is the uppermost layer of the tear film. It is generated by the meibomian glands of the upper and lower lids and prevents rapid evaporation of the aqueous layer. The orifices of the meibomian glands are located at the lid margins. If these exits are closed, the transfer of lipids to the tear film is disturbed. Therefore, it is important to keep the edges of the lids clean and the orifices of the meibomian glands unblocked.

Functions of the tear film:

  • Protection against drying of the cornea
  • Nutrition of and oxygen supply to the cornea
  • Gliding layer for the eyelids
  • Protection against foreign bodies (dust, pollen, etc.), bacteria and viruses
  • Smoothing of the optical surface of the eye for clear vision

If the composition of the tear film is disturbed, it can no longer perform properly and this may lead to infection, allergy, inflammation and the symptoms of Dry Eye.