What is dry eye?
Dry eye syndrome — also called dry eye disease (DED) — is one of the most common eye conditions worldwide and a primary reason for visits to the optometrist. Dry eye syndrome is caused by a chronic lack of sufficient lubrication and moisture on the surface of the eye or poor-quality tears. According to the American Association of Optometrists, tears are made up of three layers: oil, water and mucus. Each component protects and nourishes the front surface of the eye. A smooth oil layer helps prevent evaporation of the water layer, while the mucin layer spreads the tears evenly over the surface of the eye. If the tears evaporate too quickly or do not spread evenly over the cornea due to deficiencies with any of the three tear layers, dry eye symptoms can develop. In addition to being called dry eye syndrome, dry eye disease, or simply “dry eye,” alternative medical terms used to describe dry eyes include:
- Keratitis sicca – used to describe dryness and inflammation of the cornea usually when the layer of tears is inadequate.
- Keratoconjunctivitis sicca – used to describe dry eye that affects both the cornea and the conjunctiva.
- Dysfunctional tear syndrome – used to emphasize that inadequate quality of tears can be just as important as inadequate quantity.