Dry eyes are primarily caused by an insufficient production of tears, as stated by Mayo Clinic. The condition is common among the elderly, in post-menopausal women, those with certain medical conditions, people who undergo laser eye procedures and individuals with impaired glands. Other contributing factors include eyelid problems, drugs and environmental agents.
Tears are essential in keeping the eyes healthy and in maintaining optimal vision. These organs are constantly coated by a thin film of tears, which is divided into three layers: outer, oily layer for lubrication; middle, watery layer for moisture and inner; and mucous layer for uniform spreading over the surface of the eyes. Disturbances of the tear film can lead to dry eyes.
Dry eyes can be categorized into two types: aqueous tear deficient and evaporative. The former is characterized by a dysfunction of thelacrimal glands, which produce the middle, watery coating, while the latter is associated with swollen meibomian glands, which secrete the outer, fatty layer, as explained by the National Eye Institute.
Dry eyes are also prevalent in people with eyelid problems, including those with dermal disease on or around the folds, conjunctivitis, exposure keratitis, ectropion and entropion. Cosmetic surgery on the eyelids may also result in dry eyes. Thyroid diseases, Sjogren's syndrome, lupus, allergies and rheumatoid arthritis are also known to cause dry eyes, according to the National Eye Institute. Medications that can trigger dry eyes include decongestants, antihistamines and some anti-depressants. Wind and humid air can also lead to dry eyes.