Dry eye is a very common condition that is characterised by a disturbance of the tear film.

It causes a variety of symptoms and signs that often interfere with quality of life.

To keep the eyes comfortable and provide optimal vision, a thin, healthy film of tears coats
the surface of the eye.

This tear film is made up of three layers:

  • Lipid (oily) layer
  • Aqueous (watery) layer
  • Mucus (sticky) layer

The most superficial (top) layer is a very thin layer of lipids (fats and oils). These lipids are produced by the meibomian glands – a row of specialised oil glands along the edge of each eyelid. The main function of
this lipid layer is to prevent or decrease evaporation of the aqueous (watery) tear layer beneath. If the meibomian glands do not function properly, this leads to evaporative dry eye – where the watery tear layer has no protection from evaporating.

The middle layer of the tear film is the aqueous layer. Its function is to lubricate the eye and provide clear, consistent vision. It also has a vital role in protecting the eye from harmful bacteria and other pathogens.

These tears are produced in the lacrimal glands, situated behind the eyebrows. Often the lacrimal glands fail to produce enough tears, and this is another major cause of dry eye.
The bottom layer of the tear film is a thin mucus layer. It acts like a sheet of Velcro to attach the tear layer to the underlying cornea.