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 μl/cm2/min. At lower humidity, range was between 0.044 ± 0.013 through 0.058 ± 0.018 μl/cm2/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).
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