Purchase this article with an account.
E. I. Pearce, L. C. McCann, K. M. Barr, E. F. Connie; The Effect of Relative Humidity on the Human Tear Film. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4142.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To assess the effect of ambient humidity, using a Controlled Environment Chamber, on tear film parameters.
A newly constructed walk-in Controlled Environment Chamber (CEC) capable of producing temperatures between 5 and 35°C and relative humidity (RH) from 5 to 95% was used to expose 15 healthy subjects (mean age 21.5±2.5 years, 3M 13F) to three humidity levels, 5, 40 and 90% RH, each at 21°C. The order that subjects were exposed to the conditions was randomized using a Latin square with at least 24 hours between visits. Subjects were not informed of the atmospheric conditions. Each subject was exposed to the environment for 15 minutes prior to tear film observation. Parameters assessed were noninvasive tear break-up (NITBUT), and lipid layer thickness (Tearscope), tear evaporation rate (Servomed EP3), and ocular discomfort (visual analogue scale modified Schein questionnaire).
As humidity increased (5, 40, 90%RH) NITBUT was found to increase significantly (p=0.001) with median values of 4.8, 6.1, 9.0 seconds respectively. The lipid layer showed a significant thickening with increasing humidity (p=0.000, median grade 2.0, 3.0 and 4.0 respectively). Median evaporation rate was 40.8 gm-2h-1 at 5% RH. This dropped significantly (p=0.017) to 22.9 gm-2h-1 at 40%RH. It was found that the evaporimeter could not measure tear evaporation rate at high humidity (90% RH) for technical reasons. Total discomfort i.e. sum of dry, gritty, stinging, tired, painful and itchy question scores, decreased significantly as humidity increased. When the responses to individual questions were analyzed, dryness was the only symptom that increased at low humidity. Itchiness and stinging showed no significant change when humidity changed.
Ambient humidity has a considerable effect on the healthy human tear film. Objective signs (NITBUT, lipid layer thickness, tear evaporation rate) changed significantly as ambient humidity was altered. Symptoms, dryness in particular, showed a corresponding increase as the humidity was reduced. The role of reduced humidity on the tear film should not be underestimated, particularly as the 5% condition is commonly encountered on commercial aircraft during long-haul flight. In addition, the study illustrates that the CEC is a viable method to stress the tear film by manipulating ambient conditions.
This PDF is available to Subscribers Only