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Darcy Kroeker, Kevin van Doorn, Hendrik Walther, Lakshman Subbaraman, Lyndon William Jones; Development of a novel, objective metric to determine tear film stability. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3089.
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© ARVO (1962-2015); The Authors (2016-present)
The traditional metrics of tear film (TF) stability assessments, both subjective and objective, do not necessarily agree and may not capture all the relevant aspects of the TF that determines its stability. The purpose of this study was to develop a non-invasive objective metric (Spike Ratio Rate) to determine TF stability using keratoscopy images and compare it with existing metrics for agreement and sensitivity.
We developed an image processing program to analyze video sequences of keratoscopic images captured with a Topcon corneal topographer. At each frame, the thickness of each Placido ring in the reflected image was measured at regular azimuth increments and the difference in this thickness vector since the initial frame was computed. We defined Spike Ratio (SR) to be the proportion of all analyzed rings over which the thickness has changed by an amount exceeding a threshold value. SR Rate (SRR) was defined as the rate of change of SR, found by fitting a linear model to the SR samples over the entire time interval. The optimized method was tested on images obtained in vitro from contact lenses (CLs) imaged at 10 frames per second for 20 seconds after emergence from an artificial tear solution (ATS). The CLs included four silicone-hydrogel lens types (n=4) which were cycled daily for 4 weeks in ATS (16 hrs/day) and multipurpose solution (8 hrs/day). We computed correlations of the measured SRR values against subjective TF break up time (TBUT). An ANOVA was used to test if the mean SRR values varied between different lens materials.
37 samples were deemed suitable for analysis, resulting in 3-4 lenses of each type and 2-3 repeats for each lens. As expected, SRR correlated negatively with subjective TBUT (r2=0.67, p<0.001). Additionally, SRR was significantly different for the 4 lens types (p<0.001) and indicated the same between-lens relationships as found with subjective TBUT.
SRR is a novel metric that can be used to objectively assess the TF stability over a contact lens or the cornea. Our results demonstrate that it is sufficiently sensitive to distinguish differences in TF stability over different lens types.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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