Human tear volume, quality and evaporation: a comparison of Schirmer, tear break-up time and resistance hygrometry techniques.

A group of 10 subjects had their tears evaluated by the Schirmer and tear break-up time (TBUT) tests and their rate of tear evaporation measured by resistance hygrometry. No significant relation was found between the evaporation of the tears and the results obtained by either the Schirmer or the TBUT test. No correlation was found between the Schirmer and the TBUT test results. A significant increase in tear evaporation rate was however produced by the instillation of fluorescein during the TBUT test and by the application of Schirmer strips during the Schirmer test. It is concluded that the Schirmer and TBUT tests measure different features of the tears and these features are not related to the rate of tear evaporation.