To determine the cut-off value of the phenol red-impregnated thread test (Zone-Quick((R)), Menicon trade mark ) 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).
and methods: Fifty-four consecutive patients (including 50 females) with dry eyes, presumably related to an immune disorder, were recruited on the basis of subjective ocular symptoms and medical history (sicca syndrome). Both the phenol red thread (PRT) test and the Schirmer I test (testing periods, 15s and 5min, respectively) were performed in both eyes in random order. Only the lowest result for each test was used in statistical analyses. 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).
The ROC procedure showed that a cut-off value of 12mm in the PRT test provided the best ratio between sensitivity and specificity (56% and 69%, respectively) for the detection of 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.
Giving a cut-off value at 12mm, the sensitivity and specificity of the PRT are 56% and 69%, respectively. Even if the agreement with the Schirmer I test is highly significant, 32% of patients have discordant results. These two methods of functional assessment of tear secretion are therefore complementary and further studies remain necessary to better understand the place of both tests in clinical practice.