Dry eyes are caused by a lack of adequate tears. Your tears are a complex mixture of water, fatty oils and mucus. This mixture helps make the surface of your eyes smooth and clear, and it helps protect your eyes from infection.

For some people, the cause of dry eyes is decreased tear production. For others it's increased tear evaporation and an imbalance in the makeup of your tears.

Decreased tear production

Dry eyes can occur when you're unable to produce enough tears. The medical term for this condition is keratoconjunctivitis sicca(ker-uh-toe-kun-junk-tih-VY-tis SIK-uh). Common causes of decreased tear production include:

  • Aging
  • Certain medical conditions, including diabetes, rheumatoid arthritis, lupus, scleroderma, Sjogren's syndrome, thyroid disorders and vitamin A deficiency
  • Certain medications, including antihistamines, decongestants, hormone replacement therapy, antidepressants, and drugs for high blood pressure, acne, birth control and Parkinson's disease
  • Laser eye surgery, though symptoms of dry eyes related to this procedure are usually temporary
  • Tear gland damage from inflammation or radiation

Increased tear evaporation

Common causes of increased tear evaporation include:

  • Wind, smoke or dry air
  • Blinking less often, which tends to occur when you're concentrating, for example, while reading, driving or working at a computer
  • Eyelid problems, such as out-turning of the lids (ectropion) and in-turning of the lids (entropion)

Imbalance in tear composition

The tear film has three basic layers: oil, water and mucus. Problems with any of these layers can cause dry eyes. For example, the oil film produced by small glands on the edge of your eyelids (meibomian glands) might become clogged. Blocked meibomian glands are more common in people with inflammation along the edge of their eyelids (blepharitis), rosacea or other skin disorders.

July 24, 2015