Purpose: The fluorescein tear break-up time has long been accepted as a measurement for evaporative dry eye. The Oculus Keratograph 5M measures the tear break-up time without the need of fluorescein, nor observation by a practitioner. Two results are provided: the time it takes for any part of the tear layer to begin to break-up and the average tear break-up time as measured across multiple zones of the cornea. This study looked at the Keratograph 5M to see how repeatable the different tear break-up measurements were and how they compared to one another.
Methods: The tear film stability of 190 eyes was measured using the Keratograph Oculus 5M. The first tear-break up time (tbut-first) and the multi-zonal tear break-up average were completed, then each eye was re-measured twice more with those same tests.
Results: On 190 eyes, the mean (SD) TBUT-first scores for three consecutive measurements were 8.1 (6.8), 8.9 (6.7) and 10.7 (6.4) secs. Mean (SD) multi-zonal (avg) TBUT scores for three consecutive measurements were 10.7 (6.1), 11.2 (6.3) and 12.5 (6.1) secs. There was no significant difference between measurement 1 and 2, but the third measurement was significantly larger (p < 0.01) regardless of which method was used. Between the two metrics, the multi-zonal (avg) TBUT was significantly larger than the TBUT-first (p < 0.01). The coefficient of variability of subsequent measurements for both TBUT-first and the multi-zonal (avg) TBUT was not significantly different.
Conclusion(s): There appears to be no significant difference in the repeatability of the tear break up scores with the Oculus 5M regardless if one uses TBUT-first or the multi-zonal (avg) TBUT. However, regardless of which method is employed, one should not measure the TBUT more than twice. Introducing a third measurement in both cases caused a significantly different result, presumably due to reflex tearing.