Comparison of tear film stability assessment procedures by non-invasive and fluorescein tear breakup time measurement

We evaluated agreement and reliability of tear non-invasive breakup time (NIBUT) performed with different devices and with respect to fluorescein procedure (fBUT). Data were collected on 43 subjects (17 males; age range: 18--29 years). NIBUT was measured in a random order with different devices: EasyTear (ET), Polaris (PO) and Sirius (SI). At the end fBUT was acquired. The whole procedure was repeated (retest) 2 hours after the last measurement. BUT (s) was 12.0±7.6,12.8±6.8,14.8±8.0,8.7±5.2 in the right eye (RE) and 12.0±8.2,14.1±9.8,15.6±7.8,8.6±5.0 in the left eye (LE) with the ET, PO, SI and fBUT, respectively. ANOVA showed a significant difference between measures. All paired comparisons between BUT values were significantly different, except for ET vs. PO (RE) and PO vs. SI (LE). All correlations between NIBUT procedures resulted statistically significant. All procedures showed no difference between test and retest and ICC resulted higher for NIBUT devices with respect to fBUT. In conclusion fBUT was significantly shorter than NIBUTs. Devices cannot be considered interchangeable; however, they showed similar test-retest reliability.