What's in a Tear?

Most of us probably think our tears are made mainly of salty water but there is a lot more in tears then you think. Tears are made of three layers, all of which are vital to tear stability.

The layer closest the eye is call the mucin layer. This is a sticky mucus layer that helps hold the tears against the eyes. This layer is produced by cells called goblet cells on the white of the eye and insides of the lids. These cells can be damaged by exposure or by chemical injury. Sometimes the mucus formed is not normal and clumps together to causes mucus filaments. This can interfere with the vision and also cause dry eye.

The next layer is the aqueous layer. This is mainly water. It is produced by the lacrimal glands. The lacrimal glands are susceptible to damage from an auto-immune disorder called Sjogrens. However they may also produce too little aqueous if the nervous signal to the glands is damaged. This can happen in LASER surgery and also through taking some medications. If the aqueous layer is not sufficient the eye becomes dry we call this aqueous dry eye.

The final layer that floats on the top of the watery layer is the lipid layer. This is an oily layer which protects the watery layer from evaporating. It is produced by the Meibomian glands which line the upper and lower lids. Often the Meibomian glands get blocked and this leads to a lack of lipid layer on the tears. The tears then evaporate too quickly and the eye becomes dry. We call this evaporative dry eye.

Tears also contain lots of components of the immune system such as antibodies. When we see you at the Dry Eye Centre we take many measurements to establish which type of dry eye you have, and we develop a treatment program tailored to your needs.

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