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M Labetoulle, X Mariette, C Baudouin, L Joyaux, H Offret, E Frau; Assessment of the Cut-off Value of Phenol Red Thread in Ocular Sicca Syndrome . Invest. Ophthalmol. Vis. Sci. 2002;43(13):79.
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Purpose: To determine the cut-off value of a phenol red impregnated thread (Quickzone test®, MeniconTM) for the diagnosis of ocular sicca syndrome using the ROC (Receiver Operating Characteristic) procedure, and to estimate the agreement with the Schirmer I test (without anesthetics). Methods: 54 consecutive patients (including 50 females) with dry eyes presumably related to an immune disorder were recruited on the basis of ocular subjective symptoms and medical history (sicca syndrom). Both the phenol red thread (PRT) test and the Schirmer I test (testing periods: 15 sec and 5 min, respectively) were performed in both eyes in a random order. The same procedure was applied to 29 normal volunteers (no subjective symptoms). The patient and the control groups were matched for age and gender (mean age; 58.1 and 59,6 respectively). Only the lowest result for each test was used in statistical analyses. Results: The ROC procedure showed that a cut-off value of 12 mm in the PRT test was the one giving the best ratio between sensitivity and specificity (56% and 69% respectively) to detect dry eyes. Using this threshold, the agreement with the Schirmer I test was highly significant (kappa test; p < 10-3). However, discordant results were observed in 32% of subjects. Conclusion: The PRT has been recently proposed to assess ocular dryness. Even if the agreement with the Schirmer I test is significant using a cut-off value of 12 mm, further studies remain necessary to improve the specificity and sensitivity in the detection of aqueous-deficient dye eyes of this quick and non-invasive method.
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