The effect of low humidity on the human tear film.

PURPOSE To investigate the effect of exposure to a low relative humidity (RH) environment on tear film physiology. METHOD A controlled environment chamber was used to create 2 different environmental conditions. Ambient temperature was constant in both conditions (21°C) while the RH was set at 40% at the normal condition and at 5% in the desiccating environment. Tear evaporation, noninvasive tear break-up time, lipid layer thickness (LLT), osmolarity, ocular comfort, tear production, and ocular surface temperature were assessed in normal humidity and over a period of 60 minutes in the dry environment. RESULTS There was significant change in tear evaporation rate (P = 0.00), noninvasive tear break-up time (P = 0.00), LLT (P = 0.00), ocular comfort (P = 0.00), and tear production (P = 0.01) after exposure to the desiccating environment. No significant differences were observed between normal and dry environmental conditions in tear osmolarity (P = 0.09) and ocular surface temperature (P = 0.20). CONCLUSIONS Evaporation rate, tear LLT, ocular comfort, tear stability, and production were adversely affected by low RH. The tear film parameters observed after exposure to a desiccating environment for 1 hour were similar to those of the dry eye patient. Therefore, to avoid tear film disruption and possible ocular surface damage, the environmental conditions of dry locations need to be improved or the tear film should be protected against adverse environmental conditions.