Clinical Usefulness of the Phenol Red Thread Test as Diagnostic Tool in Dry Eye Patient

ABSTRACT

PURPOSE: To evaluate the clinical usefulness of the phenol red thread test as a diagnostic tool of dry eye by comparing the phenol red thread test, Schirmer's test and tear break-up time. METHODS: The present study included 30 dry eye patients belonging to dry eye workshop grade 1 or 2 and 25 normal subjects. Phenol red thread test, Schirmer's test, and tear break-up time were performed on each subject's right eye. The sensitivity, specificity and repeatability of each test were compared, and the correlations between the 3 tests were also analyzed. RESULTS: Tear break-up time was superior to the other tests in terms of sensitivity and repeatability. The phenol red thread test was better than Schirmer's test in terms of specificity and repeatability. In all 55 patients including dry eye patients and normal subjects, the phenol red thread test showed a greater correlation with tear break-up time than did Schirmer's test. In addition, in 25 dry eye patients, the correlation between the phenol red thread test and Schirmer's test increased significantly. CONCLUSIONS: The phenol red thread test is less irritating and requires a shorter testing time than Schirmer's test. Additionally, the phenol red thread test is superior to Schirmer's test in terms of specificity, repeatability, and relation to tear break-up time. In addition, the correlation between the phenol red thread test and Schirmer's test significantly increases in dry eye patients. Therefore, the phenol red thread test is a good substitute option for Schirmer's test in diagnosing dry eye.