Correlations in a Change in Aqueous Tear Evaporation With a Change in Relative Humidity and the Impact

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. Prospective experimental laboratory study. 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. Average evaporative rate in the higher humidity range was between 0.029 ± 0.009 through 0.043 ± 0.016 μl/cm 2/min. At lower humidity, range was between 0.044 ± 0.013 through 0.058 ± 0.018 μl/cm 2/min. Differences in the corresponding evaporative rates were statistically significant (between P < .003 through P < .043) for each analysis. 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).