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R. K. Williams, M. Senchyna, M. Wax, M. Brubaker; Comparison of Phenol Red Thread Test With Schirmer I Test for the Reproducible Measurement of Tear Production. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5326. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Measurement of tear production with a Schirmer strip is one of several fundamental tests used to diagnose dry eye. However, the clinical utility of the Schirmer test is debatable due to reported variability, poor reproducibility and low sensitivity for detecting dry eyes. Methodologically, the phenol read thread (PRT) test is similar to the Schirmer test, however it may offer several advantages that may lend to improved clinical utility. In this work, we sought to determine if the PRT test facilitated greater data reproducibility in comparison to the Schirmer I test with anesthesia.
Volunteers were recruited from the Alcon Eye Care Clinic. Closed eye Schirmer I test was performed for 3 minutes after the instillation of 1 drop of proparacaine. Open eye PRT test was performed for 15 seconds in one eye and 45 seconds in the other eye (randomized). Subjects were seen at the same time of day at each of 3 clinic visits within a 3 week period. Raw data was converted to % error of the test interval (difference in measurements / total length of measurement (30 or 75 mm)). All data was analyzed by ANOVA and Dunnett’s two-tailed comparison of means (α = 0.05).
Schirmer data from 16 subjects demonstrated no significant difference (p = 0.055) when the three sets of data were compared. The average % error of repeat measurements compared to the initial score was 18.6 ± 13.7%. 16 subjects underwent 3 separate PRT tests. No significant difference was found for either 15 sec (p = 0.834) or 45 sec (p = 0.44) tests. The average % error of repeat measurements compared to the initial score was 6.27 ± 4.71 % and 9.91 ± 8.45 % for 15 sec and 45 sec tests, respectively.
Of the three tests of tear production that were evaluated, it appeared that the PRT test applied for 15 sec was the most reproducible, although from a user-friendly perspective, the 45 sec PRT test was best as it facilitated the most accurate delineation of fluid migration along the thread. Additional studies are planned to better characterize the clinical utility of the PRT test in the diagnosis of dry eye.
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