Increased Evaporative Rates in Laboratory Testing Conditions Simulating Airplane Cabin Relative Humidity: An Important Factor for Dry Eye Syndrome

Purpose. To quantitatively explore the relationship between low relative humidity conditions, as experienced in airplane cabins during flight, and increases in aqueous tear evaporation as a potential explanation for increased dry eye symptoms noted by people when in low humidity environmental conditions. Methods. Prospective experimental laboratory study. Evaporative rates under two different ranges of increasing relative humidity, from 20% to 25% (similar to the relative humidity in airplane cabins or arid regions) and from 40% to 45% (similar to the relative humidity in nonarid regions), were obtained from 18 patients with dry eye and 11 healthy subjects. Results. Statistically significant differences were found within all groups: patients with dry eye (divided into keratoconjunctivitis sicca [P=0.001] and meibomian gland dysfunction [P=0.007]) and healthy subjects (P≤0.001). The mean increase in evaporative rate across all study subjects was 99.72% (P≤0.001) when the eyes were exposed to the lower humidity condition. Conclusions. These studies quantitatively show the negative impact of environmental low relative humidity conditions, including those associated with commercial airplane travel, on aqueous tear evaporation dynamics. The increased evaporative rate is similar in healthy subjects and patients with dry eye. These findings provide useful data for the development and evaluation of treatment paradigms for any person who notes dry eye symptoms in low relative humidity environments.