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Wing Li, Andrew D. Graham, Meng C Lin; Repeatability of Ocular Surface Cooling Measurement. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2850.
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© 2017 Association for Research in Vision and Ophthalmology.
Increased tear osmolarity resulting from excessive tear aqueous evaporation is considered to be responsible for the symptoms experienced with evaporative dry eye. In addition, tear hyperosmolarity has been linked with long-term pro-inflammatory changes to the cornea, which may in turn disrupt the corneolacrimal neural loop. Currently, there is no clinical tool that can be used to measure tear evaporation directly. Recently, our group found that measuring ocular surface temperature (OST) could indirectly measure tear evaporation rate. The clinical potential of OST measurement is currently unknown, as a repeatability profile of OST has not been established.
Prior to each measurement, subjects were acclimated to the examination room environment for 10 minutes. Subjects were asked to close their eyes for two minutes and then open their eyes and refrain from blinking for as long as possible while the OST was measured using an infrared thermographer (FLIR A655sc). Subjects were seen for two visits, with the visits separated by at least one week; morning (AM) and afternoon (PM) measurements were taken at each visit. Intra- and inter-day repeatability was assessed by Intraclass Correlation Coefficient (ICC) and Limits of Agreement (LoA). Intra-day ICC was calculated from the mean AM and the mean PM measurements from the two visits. Inter-day AM and PM ICC were calculated separately for the two AM and two PM measurements, respectively.
Thirty four subjects (all female) completed the study. The grand mean ocular surface cooling (OSC) rate was 0.089oC/s (range: 0.002-0.270oC/s), with no significant inter- or intra-day differences in OSC rate (paired t-test; p=0.82 and 0.87, respectively). The intra-day ICC was 0.49, and the 95% LoA for intra-day OSC rate measurements were -0.099 – 0.103oC/s. Inter-day AM ICC was 0.72, with 95% LoA of -0.085 – 0.087oC/s. Inter-day PM ICC was 0.47, with 95% LoA of -0.102 – 0.117oC/s.
OSC measurements demonstrated relatively poor intra-day and inter-day PM repeatability but good inter-day AM repeatability. This likely reflected the variability in environmental factors and visual demands that subjects encountered before their PM measurements. The good inter-day AM repeatability suggests that infrared thermography may be useful in monitoring evaporative dry eye; however, more work is needed to determine its clinical potential.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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