Biology of Dry Eye

The tear film is made up of three layers: the inner mucin layer, the middle watery aqueous layer, and the outer oil/mucin layer. The tear film exists for a few different reasons including the first part of the eye to refract light, to protect the eye from foreign entities, and to lubricate the outer structures of the eyeball. If any one of these layers is deficient the tear film will not function properly and dry eye symptoms will occur. The most common reasons for Dry Eye Syndrome are decreased tear production and poor tear quality.
Poor Tear Quality/Meibomian Gland Dysfunction (MGD)

The most common problem contributing to Dry Eye Disease is Meibomian Gland Dysfunction, or MGD. MGD is responsible for 86% of dry eye patients. The Meibomian Glands are located close to the edge of the eyelids and secrete the “meibum” or oil that is the outermost layer of tears. When there is less oil in that layer, the middle “watery” tear layer evaporates much faster contributing to the symptoms associated with dryness. In most cases, the Meibomian Glands do not function properly due to inflammation of the glands themselves and the structures around the glands.

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There are other reasons for poor tear quality as well, including:

  • Infrequent Blinking (commonly associated with increased computer/tablet use)

  • Wind, smoke, smog, air quality

  • Eye Allergies

  • Blepharitis (inflammation of eyelids around eyelashes)

  • Vitamin A deficiency

  • Eyelid laxity/tightening (ectropion/entropion)

Decreased Tear Production
Any of the three tear layers can experience a decrease in tear production. The most common reason for decreased tear production is age. Unfortunately, there is nothing we can do about that. There are other reasons that can contribute to decreased tear production, including:

  • Medical conditions

    • Sjogren’s Syndrome

    • Lupus

    • Scleroderma

    • Rheumatoid Arthritis

    • Thyroid Disease

  • Side Effects from medications such as antihistamines, decongestants, antidepressants, and retinoids (anti-aging and anti-acne medications)

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