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Dry EyesYour eyes constantly produce tears. Dry eyes is a condition where you simply don’t have enough tears in your eye. The tears are in intricate mixture of water, salts, fat and bug fighting chemicals. When you blink, the lids wash the tears over the front surface of the eye before they drain out via two little holes in the corner of you eye. These holes drain into your nose, which is why your nose runs when you cry.
If you don’t produce enough good quality tears then the tear film becomes weak and unstable and breaks down before the lids have a chance to renew the layer with a blink. This causes dry spots on the surface of the eye which rips the cells underneath causing discomfort and irritation.
Good healthy tears have three separate components:
1.) Mucous, from the goblet cells deep inside the eyelid. 2.) Water and salts from lachrymal gland. 3.) Oil, from the Meibomian glands in the eyelids.
The Mucous layerThis connects the tear film to the eye's surface and serves as a bio-glue for whole tear film. It is formed by the secretions of 10 million tiny goblet cells living within the white of the eye and inner lid surfaces. The Aqueous LayerOn top of the mucous is a watery or aqueous layer. This is produced by one large lacrimal gland which is located just below the eyebrow. During wakening hours, the lacrimal gland pumps aqueous tears at a background level adjusting for environmental conditions. When there is an irritant, extra "crying" tears are made almost instantly. This is why as odd as it sounds many dry eye sufferers experience watery eyes- the lacrimal gland swings into action as the dry spots damage the cells on the front of the eye, which causes a gritty, burning sensation. During sleep the lacrimal gland is less active which is why eyes feel sore and dry upon wakening.
The Lipid layerThe lipid layer sits on top of the watery layer - sealing the tear film by preventing evaporation. This oil is derived from fats exuded from twenty three meibomian gland openings along the edge of the eyelids. Blocked or poorly functioning meibomian glands cause problems with the lipid layer. If the sealing layer of fat is faulty then there is nothing to stop the watery tears just evaporating away. This then leads to dry eye caused by excessive evaporation. This is called meibomitis or posterior blepharitis and is a chronic recurring condition. Are these lifestyle factors causing your dry eyes?Dry eye cases have nearly doubled over the last seven years and the list of lifestyle factors is huge. Central heating, air conditioning, dehumidifiers, hairdryers, car windscreen demisting, altitude; air travel, dry climates, wind, air pollution, saunas, spicy foods, alcohol, contact lenses; and activities that decrease blink rate, such as driving, watching TV, computers and reading, all increase tear evaporation as well.
Could these medications be causing dry eye?Antidepressants, decongestants, antihistamines, blood pressure medication, diuretics, ulcer medication, tranquillisers, beta blockers, oral contraceptives can all dry out your eyes. Is your maturity a factor?Although dry eyes can be a side effect of disease, the most common cause is normal ageing. In fact the volume of lubricating background tears is less than half at age 65 than at age 18. Not surprisingly then, dry eyes affects one in five people over 55, but some more than others. People with wider eyes; those with larger than average tear duct openings are worse off.
For women, hormonal changes brought on by pregnancy, lactation, oral contraceptives, menstruation, and post-menopause can cause dry eye conditions.
Laser Eye SurgeryDry eyes are a confirmed side effect in 30% of cases. Several diseases result in secondary Dry Eye SyndromeRheumatoid Arthritis, Thyroid Abnormalities, Asthma, Sjogren's Syndrome, and Lupus. 
The commonest treatment for dry eyes is artificial tears. Many of these artificial tearts have a preservative, Bezalkonium Chloride, to stop bugs getting into the fluid once the lid has been opened. Bezalkonium Chloride has been shown to suppress the function of Goblet cells over time, making the eye dryer! Choose either unpreserved artifical tears or ones without Benzalkonium Chloride.
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