Optimization of the Phenol Red Thread Test for Assessment of Ocular Dryness in Sjögren’s Syndrome

Abstract

Abstract: : Purpose: To optimize the phenol red thread test procedure for diagnosis of dry eye syndrome. Methods: 63 consecutive patients complaining of ocular dryness secondary to Sjogren's syndrome were included in the study. Using the Zone–Quick® (Menicon^TM) device, the phenol red thread test (PRT) was performed before (PRT1) and after (PRT2) the Schirmer I test. Only the lowest value of both eyes was retained for each test. The same procedure was applied to 31 healthy volunteers. The patient and the control groups were matched for age and gender (mean age; 56.5 and 52.7 respectively). The cut–off values were assessed using the Receiver Operating Characteristic (ROC) procedure and agreements between Schirmer I and either PRT1 or PRT2 were assessed with the kappa test. Results: The best cut–off value for PRT test in usual conditions (PRT1) was 12 mm whereas 14 mm should be used as threshold when PRT was performed after drying out the tears (PRT2). Sensitivity and specificity of PRT2 were respectively 0.62 and 0.92 versus 0.49 and 0.77 for PRT1, respectively. Agreement between PRT2 and Schirmer I tests was highly significant considering that 79.8% of the subjects had similar qualitative results, i.e. normal or abnormal, with the both procedures (kappa index: 0.59; p < 10^–10). No patient described ocular discomfort during the PRT test procedures. Conclusions: Drying out the lachrymal meniscus before proceeding to PRT test provides both a highly sensitive and specific method for dry eye diagnosis. Since PRT test causes less discomfort and is quicker than Schirmer I, it could be used more frequently in a daily practice for the screening of dry eye syndrome.

Keywords: cornea: clinical science • cornea: tears/tear film/dry eye • clinical (human) or epidemiologic studies: systems/equipment/techniques