Effect of blinking on repeatability of measurements of tear meniscus curvature

Purpose: To determine by optical coherence tomography (OCT) the influence of blinking on repeated measurements of tear meniscus curvature (TMC). Methods: Normal human (n = 21) eyes were imaged to get dimensions of the lower tear meniscus (LTM). On the day before the OCT imaging, all enrolled subjects were tested by McMonnies questionnaire, fluorescein tear break-up time (FTBUT), fluorescein staining of ocular surface, Schirmer I test, a slit examination of the lid margins and meibomian glands. All ocular surface images were obtained immediately (method 1) or 2 seconds (method 2) after a blink, and were repeated on the next day. All examinations were conducted in the same conditions of temperature, brightness, humidity and time of the day. Results: The average TMC was 646.90 ± 513.43 μm and 563.10 ± 24.28 μm, by method 1 and 2, respectively. In the second case, reliability analysis has revealed a good consistency of measurements (ICC=0.99, p<0.01). Conversely, no significant agreement was obtained for measurements by method 1 (ICC=0.4, p=0.39). Comparing the two systems, we did not found a significantly statistical correlation between the results (ICC=0.09, p=0.39). Conclusions: Blinking plays a crucial role in dynamic distribution human tears and in determining changes of dimensions of tear meniscus. The standardization of OCT imaging of the ocular surface appears to be necessary to aim a significant repeatability of tear meniscus measurements and a better comparability of results.