The cotton thread test: a brief review and a clinical study of its reliability on Hong Kong-Chinese.

Fifty-four asymptomatic Hong Kong-Chinese subjects were recruited and their lacrimation was assessed using a modified cotton thread test (CTT). The CTT was performed once on each subject and, for seven subjects, the test was repeated seven times on different days over a period of 2 weeks to test the reliability of the CTT. The mean (+/- SD) CTT value (length of wetting of thread in millimeters for a 1-min testing period) of this group of subjects was 22.8 (+/- 9.4) mm/min. Repeated measures analysis of variance revealed no significant difference in the CTT values made on different days. The CTT was found to be superior to the conventional Schirmer test in terms of comfort and consistency of results obtained. A brief review of some studies and results reported by previous investigators using the CTT is also presented for comparison.