Interexaminer difference and the effect of training on the phenol red thread test results in Hong Kong-Chinese

Purpose. This study evaluated interexaminer agreement in the measurement of tear volume using the phenol red thread (PRT) test on Hong Kong-Chinese subjects. The effect of an intensive training session on interexaminer agreement was also investigated. 

Methods. Three postgraduate students without an optometry background were introduced to the use of the PRT test. After a general introduction (including a demonstration and some practice among themselves), the examiners collecting the first set of data from 38 subjects. They were then given an intensive 30-min training that involved strict standardization of instructions/procedures and practice. PRT values were collected from 27 subjects (four subjects participated in both phases of the study) after the intensive training. 

Results. Significant differences were found among the examiners before and after the intensive training, which was mainly due to examiner 1, who consistently obtained relatively lower mean PRT values in both testing sessions. The intraclass correlation values estimated for all examiners were 0.35 and 0.58 before and after the training session, respectively. The 95% limits of agreement after the training session ranged from -14.8 to 8.0 mm/15 s between examiners 1 and 3, who showed the largest difference, and from -8.8 to 9.3 mm/15 s between examiners 2 and 3, who showed the smallest difference. The latter pair also showed the most significant increase in agreement after the intensive training (intraclass correlation value increase from 0.29 to 0.65), although no significant differences in the PRT results were found between the two examiners before and after training. 

Conclusions. Our results suggest that the interexaminer agreement of PRT results is influenced by both examiner- and training-specific factors. Intensive training is important for ensuring the highest consistency among examiners. The moderate interexaminer agreement suggests that clinicians should seek a substantial difference in tear volume when making decisions regarding interventions for their Hong Kong-Chinese patients. Copyright © 2003 American Academy of Optometry.