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J. N. Cohen; Fluorescein Drops Produce Wider Mires Than Strips. Invest. Ophthalmol. Vis. Sci. 2010;51(13):587.
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To determine if fluoroscein drops used to stain the tear film for applanation tonometry produce wider mires than the application of wet fluorescein strips after tetracaine. Background: Hans Goldmann noted in his original 1957 study of applanation tonometry that the mire must be maintained "meticulously" at a width of .2mm in order to avoid deviations in the measurement of IOP. An excess of fluid surrounding the probe can create deviations of up to 2mmHg. No studies have compared the distribution of mire widths between the two most common methods of staining, to determine if one method is preferential.
143 patients have randomly received either a drop of fluorecein benoxonate solution or a wetted strip of fluorescein following tetracaine. The technician recorded the time from instillation of dye and the width of the mire using a digital camera mounted on the slit lamp. The distribution of mire widths have been compared.
Mean mire widths vary significantly, with Fluorescein benoxonate drops yielding an average of .44mm and the fluorescein strip yielding .30mm (P<.001). Fluorescein drops yield mires of declining width within the five minutes after drop application (p=.017).
The difference in mean mire width may contribute to erroneously high readings with the use of a fluorescein drop. To avoid this, waiting a few minutes after application of the dye is advised.
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