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A McLean, D Renner, N Himebaugh, H Liu, Y Guo, C Begley; Comparison Of Three Different Methods For Observing Tear Break-up . Invest. Ophthalmol. Vis. Sci. 2002;43(13):84.
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Purpose:The purpose of this study was to compare two non-invasive methods for observing tear break-up, the Tearscope PlusTM (TS) and retroillumination of the tear film (RI), to the traditional fluorescein (FL) method. Methods:The eyes of 10 normal subjects were dilated with 1.0% tropicamide to enhance viewing of the RI and TS image, and to quickly alternate among the three methods. After a period of 30 min, eyes were anesthetized with 0.5% proparacaine to allow subjects to keep their eyes open. While holding one eye closed, subjects were asked to keep the experimental eye open while the patterns of tear film disruption were videotaped alternately by the 3 techniques (TS, RI, and FL). Relative tear thickness maps by pixel density were then generated, when possible, for each type of illumination (MATLAB program). Results:Tear break-up and thinning were easily detectable by the traditional method of FL over any part of the cornea. RI showed tear break-up with high resolution over the retroilluminated area of the pupil. RI is an optical technique which appears to be an edge detector for tear film thickness differences. RI did not differentiate between large areas of surface drying and an intact tear film of even thickness (which occurred in this study secondary to anesthetic use and extended eye opening). Areas of tear break-up were sometimes identifiable by TS, but tear break-up was often poorly visible, difficult to localize, or obscured by the lashes and other reflections. The spatial distribution of early tear break-up was highly correlated (r=0.79) between the RI and FL methods, but RI was less accurate when large areas of surface drying were present. Image analysis of tear film thickness differences was possible with FL and RI, but was difficult with the TS due to the low contrast, confusing image. Conclusion:RI produced an easily detected, high resolution image of tear break-up within the pupil that was highly correlated with the FL method unless large areas of surface drying were present. Tear break-up was more difficult to identify and quantify using the TS, rendering it less useful as a non-invasive method for measuring tear break-up.
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