A pilot study of the comparative performance oftwo cotton thread tests for tear volume

Abstract

Tear volumes of 15 normal Hong Kong (HK-Chinese were measured using a cotton thread test (CM and the phenol red thread (PRT) test on 6 different days. The results showed that both CTT and PRT tests performed on normal subjects were reliable over time. The mean CTT and PRT values were 11.8 (±4.4)mm/15s and 15.4 (±4.9)mm/15s respectively. There is a significant difference between the CTT values and the PRT values so the two tests cannot be used interchangeably. There is a day-to-day variation in both tests which may be clinically significant for some subjects and we suggested that more than one measurement be taken when an accurate tear volume measurement is important for the management of the patient. We also compared our PRT results with those of previous investigators and found that the mean PRT value is significantly lower in HK-Chinese subjects than in Caucasian subjects, while no difference was found between HK-Chinese and Japanese subjects.