Tears are comprised of three layers: oil, water, and mucus. Each layer plays a key role in keeping the eye lubricated. For example, the oil layer prevents the water layer from evaporating, while the mucin layer spreads tears evenly. Should any layer prove insufficient, it will result in eye dryness.
Factors such as age, gender, medications, and certain medical conditions can all affect your body’s ability to produce good quality tears. Even your environment can cause the water layer to evaporate too quickly. Just as there are multiple causes of dry eye, there are multiple kinds as well.
Evaporative dry eye is caused by a lack of oil in tears, resulting in the water layer evaporating too quickly. Aqueous deficient dry eye, on the other hand, is when tears do not contain enough water to keep eyes nourished. Which kind of dry eye you have will dictate which treatment you receive.