What Causes Dry Eyes?
Evaporative Dry Eye
Tears are made up of three layers (oil, water, and mucus), and each layer has a specific purpose to keep the eye lubricated. If something is wrong with your tears’ oil layer, tears will evaporate too quickly or not spread evenly, which causes evaporative dryness.
In an attempt to correct this dryness, your lacrimal glands (the tear glands) produce more watery tears, which do not stay on your eyes and often run down your cheeks instead.
Aqueous-Deficient Dry Eye
While evaporative dryness leads to too many watery tears, aqueous deficiency comes from too few watery (or aqueous) tears. This can happen because your tear glands are damaged or not functioning properly, which can be caused by inflammation or by certain medications.