Correlations in a change in aqueous tear evaporation with a change in relative humidity and the impact

PURPOSE: To establish scientific relationship between relative humidity (RH) and aqueous tear evaporation to elucidate possible significance of this relationship in normals and aqueous tear deficiency patients. DESIGN: Prospective experimental laboratory study. METHODS: Ocular surface evaporation was determined using evaporometry and calculated for two ranges of RH, 25% to 35%, and 35% to 45% in a randomized clinical patient population. RESULTS: Average evaporative rate in the higher humidity range was between 0.029 +/- 0.009 through 0.043 +/- 0.016 mu l/cm(2)/min. At lower humidity, range was between 0.044 +/- 0.013 through 0.058 +/- 0.018 mu l/cm(2)/ min. Differences in the corresponding evaporative rates were statistically significant (between P <.003 through P <.043) for each analysis. CONCLUSIONS: A decrease of 10% RH resulted in an average difference of between 28.33% to 59.42% increase in evaporation. The increase in evaporation at lower humidity has significant clinical implications for patients with aqueous deficient dry eyes, and possibly those undergoing laser-assisted in situ keratomileusis (LASIK).