Tear meniscus changes during cotton thread and Schirmer testing

PURPOSE. TO elucidate the effect of the cotton thread test (CT-T) and Schir mer test (S-T) on the tear reservoir by evaluating the radius of tear menis cus curvature. METHODS. The radii (R) of the central lower tear menisci were measured by a newly developed video meniscometer in 11 eyes of 11 normal volunteers (6 m en, 5 women; mean age, 27.7 +/- 3.6 years [SD]) and 9 eyes of 9 patients wi th tear deficiency and severe dry eye in whom the puncta had been therapeut ically occluded (9 women; mean age, 50.6 +/- 10.4 years). In this dry eye g roup, the absence of reflex tearing, coupled with the absence of lacrimal d rainage due to punctal occlusion allowed more precise observation of the re moval of tears from the meniscus. A 1-minute CT-T was performed, followed a fter an interval of 10 minutes by a 1-minute S-T. Tear meniscus curvature w as documented before (R-0) and during the tests at 30 seconds (R-30) and GO seconds RESULTS. In the normal group, respective R values (CT-T; S-T; mean +/- SD m m) were R-0 (0.26 +/- 0.11; 0.26 +/- 0.07), R-30 (0.27 +/- 0.16; 0.20 +/- 0 .13), and R-60 (0.29 +/- 0.15; 0.23 +/- 0.21); and in the dry eye group, re spective R values (CT-T; S-T) were R-0 (0.59 +/- 0.23; 0.51 +/- 0.19), R-30 (0.52 +/- 0.25; 0.22 +/- 0.09), and R-60 (0.51 +/- 0.19; 0.21 +/- 0.08). I t was demonstrated in the dry eye group that R was diminished more by the S -T than by the CT-T in the time course of the measurement (P = 0.01). In th e dry eye group alteration of R occurred within the first 30 seconds, and i n this group significant correlation was found between R-0 and the S-T resu lt (r = 0.67; P = 0.05), and between R-60- R-0 and the S-T result (r = -0.8 1; P = 0.01). Also, there was a significant correlation between R-60- R-0 a nd the S-T result in the normal group (r = 0.71; P = 0.02). There were no s ignificant correlations between R-0 or R-60- R-0 and the CT-T results in ei ther group. CONCLUSIONS. These studies afford some insight into the dynamics of the Sch irmer test, suggesting that wetting is influenced by the negative hydrostat ic pressure within the tear meniscus. With the protocol used, no conclusion could be drawn about the relation between meniscus radius and wetting of t he cotton thread.