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Patrick Johnston, John Rodriguez, Keith J. Lane, George W. Ousler, III, Mark B. Abelson; Inter-Blink Interval Patterns in Dry Eye and Normal Subjects. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3843.
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Blink rates are frequently higher in mild to moderate dry eye subjects than in normal subjects. Equivalently, mean inter-blink intervals (IBIs) are shorter in dry eye subjects than in normal subjects. The purpose of the present study was to extend the comparison to other aspects of the IBI distribution, in particular, to variances and correlations over time. The outcomes of this study could be used as a technique to diagnose dry eye subjects and assess therapeutic effects.
Blinks were captured over a 10 minute period for 10 normal subjects and 10 subjects diagnosed with dry eye. The visual task assigned to subjects consisted of viewing a documentary. For each subject, the sequence of blinks was transformed to a time series of IBIs measured on the log scale, with blink number representing time. Means, variances, and autocorrelations were calculated for each subject’s IBI distribution and used to make simple comparisons between normal and dry eye groups. More formally, groups were compared by a random effects model with an autoregressive covariance structure. To assess reproducibility, 7 of the 10 normal subjects had replicate measurements taken at a second visit, and IBI means and variances were compared between visits.
Mean IBIs were 2.1 times longer in normal subjects than in dry eye subjects. Further, IBI variability and IBI autocorrelation were higher in normals than dry eyes by 2.0 and 1.8, respectively. All comparisons were statistically significant at the 5% level. In addition, measurements of IBI means and variances appeared to be reproducible based on the 7 subjects measured at 2 visits. For example, means and standard deviations at visit 2 were within 10% of those at visit 1.
As expected, normal subjects had longer IBIs than dry eye subjects. Less expected were the findings that normals also had higher variability and autocorrelation in their IBIs. These results are suggestive of a lower capacity to control blink rates in dry eye subjects.
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