Essentially, Dry Eye Syndrome is caused by three things :
1. Reduced tear production
2. Increased tear evaporation
3. An abnormality in the production of mucus or lipids
Reduced Tear Production
Age, hormonal changes and some medical conditions (Sjogren Syndrome, rheumatoid arthritis or lupus) can cause a decrease in the production of the aqueous layer. Some medications (antihistamines, antidepressants and beta-blockers) may also cause a reduction in tear production.
Increased Tear Evaporation
Tear evaporation is often caused by a reduction in the lipid layer (which protects the aqueaous layer). If you cannot or do not blink often enough, evaporation will also increase. Notably, computer use is a cause of dry eyes because we do not blink enough when staring at the screen. This is also true when watching television or reading. Some medical conditions (Bell's Palsy) may affect the ability to blink and, hence, result in dry eyes.
Abnormalities In Mucus Or Lipid Production
One cause of increased tear evaporation is a reduction in mucus or lipid production. This is an issue in its own right as it can be caused by Blepharitis and other related conditions.
Abnormal production of mucus can result from damage to the eyes (chemical burns, etc) and will stop the tear film from being spread over the eyes. Poor lipid production is often assosicated with Blepharitis and Rosacea.
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