Comparative study of two non-invasive tear film stability techniques

This study was conducted to establish normative and comparative data from healthy subjects under uniform ambient conditions for two non-invasive tear breakup methods (the HIR-CAL grid-modified keratometer and the Mengher-Tonge xeroscope). The study also sought to establish the repeatability and inter-observer variability of the two methods. Forty-five subjects between the ages of 18 and 45 with no known dry eye conditions and with normal ocular health were assessed. Both methods were performed on one eye (both the eye and the first method of testing were randomly selected). On a direct comparison basis, we found that the keratometer method, as has been reported, yielded shorter (generalized sign rank test, n = 58 paired comparisons, p < 0.0001) non-invasive breakup times (NIBUTs) than the xeroscope (mean > or = 35.6 +/- 19.2 seconds and mean > or = 44.7 +/_ 16.3 seconds (mean +/- s.d.), respectively). The keratometer NIBUTs were longer than reported values. The different-day, same-subject repeatability of the NIBUTs as measured by both instruments was excellent. The inter-observer comparison indicated that examiner differences may exist, although the sample size for this assessment may have limited the strength of the comparison.