The airplane environment tends to be one of the driest environments that we are exposed to for hours at a time. Furthermore, the air pressure in an aircraft cabin is much lower than sea level. Water evaporates faster in low humidity environments, as well as in decreased air pressure. Finally, each seat has air vents overhead that often are directed at or near the face. The result is a significantly increased rate of tear evaporation that brings about symptoms of dry eyes. Maintaining a healthy natural tear film is imperative to comfortable air travel for the eyes.
