In many cases, dry eye results from disorders of the various glands which work together to produce normal tears. Tears themselves are a complex combination of substances which form three layers on the eye. The very thin outer layer contains lipids from the meibomian glands in the eyelid, to reduce evaporation. The lacrimal glands produce the middle watery layer that keeps the salinity and the acidity of the tears at proper levels. This middle layer also carries antibodies and other immune defense agents to defend the eye against infection.
Many different things cause dry eye syndrome.
The normal aging of tear glands, as well as specific diseases and disorders, may cause changes in the amount and condition of tears produced. Decreased sensitivity of the cornea can also lead to insufficient production of tears. Excessive evaporation of tears can also cause dry eye syndrome. People with unusually large eyes, as well as those who suffer from thyroid disease, may also experience dry eye syndrome caused by excessive evaporation. Dry eye can also result from unusual facial anatomy or irregularities in the cornea, resulting in uneven or inadequate tear coverage of the eye.