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L. C. Espirito Santo, A. J. Cariello, F. C. Oliveira, M. Hosoume, D. Freitas; Comparative Study of Schirmer's I and Phenol Red Thread Tests. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5327.
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To investigate the relation between Schirmer's and Phenol Red Thread tests comparing results, discomfort scale and the interference of these tests on Rose Bengal test performed just after.
After obtaining approval from the institutional ethic committee from UNIFESP, volunteers were invited to participate of this study. At the first day, all subjects underwent Schirmer’s I test , visual analogical discomfort’s scale and Rose Bengal test. On the next day, they underwent the Phenol Red Tread test, visual analogical discomfort’s scale and Rose Bengal test. At Schirmer’s I test (without topical anesthesia) a value < 10 mm was taken as abnormal and at Phenol Red Thread test patients with dry eye have wetting values < 10 mm. The values of Phenol Red test were compared to Schirmer’s values which were considered a gold standard dry eye test. The Rose Bengal test was done by Van Bijesterveld’s scoring. The collect of results was performed in a blind way.
Twenty volunteers were included. The age ranged from 25 to 75 years with mean of 51.50 ± 15.96. Sixteen (80.00%) patients were females. The Schirmer`s I test mean was 18.37 mm ± 10.57. The result was positive in 30% (12/40 eyes). The Phenol red thread test mean was 12.45 mm ± 5.41 and it was positive in 27.50% (11/40 eyes). Comparing both tests, the sensibility and specificity of Phenol Red test were 58.33% and 85.71%, respectively. The positive predictive value was 63.63% and the negative predictive value was 82.75%. The mean of analogical discomfort scale was 4.20 ± 2.52 for Schirmer’s test and 0.85 ± 1.14 for Phenol Red test (p<0.001). The mean of Van Bijesterveld’s scoring performed after Schirmer`s I test was 3.75 ± 1.92 and after Phenol Red test was 2.40 ± 2.34 (p<0.001).
The Phenol Red Thread test presented a high specificity and however had a low sensibility compared to Schirmer’s I test. The Schirmer's I test provoke more discomfort and damage to the ocular surface than Phenol Red Thread test, being able to hyper estimate the result of the Rose Bengal test when performed just after.
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