Phenol Red Thread Test Vs Schirmer's Test: a Comparative Study

Aim: To measure the agreement between Schirmer's and phenol red thread tests in detecting dry eyes.

Patients And Methods: A total of 103 patients attending preoperative cataract assessment clinic who agreed to be involved in the study were recruited. Each patient had one eye examined by both tests in a random order by two different investigators who were unaware of the results of the other test. Dry eye symptoms were assessed using an interviewer-administered questionnaire. The data were collected after the study period and analysed using kappa statistics to assess the agreement between the two tests.

Results: Schirmer's test was positive in 25 patients when a cutoff point of 5 mm was used and positive in 41 patients with a cutoff point of 10 mm. Phenol red thread test was positive in four patients when a cutoff point of 10 mm was used and in 32 patients with a cutoff point of 20 mm. Kappa ranged from 0.067 to 0.3 indicating very weak agreement between the two tests. In all, 27% of the patients had symptoms of dry eyes; however, the agreement between each test and the symptoms was very poor.

Conclusion: There is very weak agreement between Schirmer's test and phenol red thread tests and between each test and symptoms of dry eyes.