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Meng C Lin, Andrew D. Graham, Thao Yeh, Tiffany Yuen; Fluorescein tear breakup time measurement disrupts tear film stability. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2495.
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We aim to provide insights into the discrepancies between results from non-invasive (NI) and invasive methods of measuring tear breakup time (TBUT). We hypothesize that an invasive method can potentially perturb the tear lipid layer causing a previously stable tear film (TF) to break up prematurely; a greater proportion of TFs would be expected to be assessed as unstable with an invasive method, compared with a NI method.
Tear film stability (TFS) was assessed on 101 subjects, with measurement of NITBUT using a Medmont E300 corneal topographer followed by invasive TBUT using NaF dye (FTBUT) on strips. A second cohort of 137 subjects was similarly measured, but with 2 μl of 0.35% NaF instilled by micropipette.
A stable TF was defined as TBUT>10s. In the cohort whose NaF was applied by strips, 55% of eyes exhibited unstable NITBUT and FTBUT; 8% stable NITBUT and FTBUT; 35% stable NITBUT but unstable FTBUT; 2% unstable NITBUT but stable FTBUT. A higher proportion of TFs was assessed as unstable with the invasive method, compared with the NI method (p<0.001). In the cohort whose volume of NaF dye was controlled, 33% of eyes exhibited unstable NITBUT and FTBUT; 36% stable NITBUT and FTBUT; 19% stable NITBUT but unstable FTBUT; 12% unstable NITBUT but stable FTBUT. No significant difference was found in the proportion of unstable TF between the invasive and NI methods (p=0.101). There was a higher proportion of stable TF assessed as unstable with NaF strips than with 2µl NaF (35% vs. 19%; p=0.001). There was a higher proportion of unstable TF assessed as stable with 2µl NaF than with NaF strips (12% vs. 2%; p=0.001).
Discordance between NITBUT and FTBUT occurred 37% and 31% of the time with F strips and 2µl NaF, respectively. NaF dye delivered using a strip, presumably more invasive compared with 2µl NaF delivered by micropipette, further decreased TBUT, thus contributing to the discordance between results from the different methods of TFS assessment. Conversely, cases of short NITBUT but long FTBUT may be due to an uneven TF that appears stable with NaF (i.e., no dark spots but areas of NaF intensity appear differently) but unstable by distortion of the mires with the NI method. Further investigation is warranted to determine the optimum volume of NaF dye required to induce minimum disruption to the TF, and the optimum endpoint for NITBUT assessment.
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