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Stefan Arnold, Melanie Gillner, Timo Eppig, Achim Langenbucher; Diagnosis of Dry Eye - Measurement Setup for Non-Invasive Analysis of the Dynamic Tear Film Behavior. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3800.
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To build up a non-invasive measurement setup for consecutive analysis of the human tear film behavior, in particular to examine simultaneously the dynamic behavior of the lipid layer and the tear film break-up. For proof of concept twelve volunteers were examined.
The measurement setup consisted mainly of an illumination unit, a Placido grid projector, two CMOS-cameras, a beam splitter and an objective. The illuminated pattern was reflected off the subject`s tear film and the first camera allowed for time-course image acquisition of the reflected grid. With the help of the beam splitter and the second camera the subject’s tear film lipid layer was recorded simultaneously on a common axis. An individual lens for each camera - integrated between the beam splitter and the CMOS sensor - and the objective provided adequate image quality. The entire setup was attached to a three dimensional motion stage. The subject’s head was fixed to a chin rest during measurement and the setup was aligned to the optical axis of the eye to be examined. Aligning and focusing were done manually and controlled by the examiner as well as starting and ending of the simultaneous time-course image acquisition. At least one inter-blinking period - including lid opening and closing - was recorded for each eye of twelve healthy subjects.
Changes and distortions in the time course of the Placido grid images indicated break-ups of the tear film layer. The initial break-up time (BUT) was determined by three independent observers for each of the twelve examined subjects. The last image showing a totally closed lid was defined as reference point in time. Subsequently after lid opening, lipid movement was shown in the images of the second camera until the lipids remained in position. The lipid movement time (LMT) was determined by the observers.
With the setup temporal dynamics of the human tear-film were detectable. In order to analyze the human tear film the LMT specifies the condition of the lipid layer, while the BUT specifies the behavior of the entire tear film. Abnormal values indicate a pathologic tear film behavior. Therefore, we consider this approach to be usable in clinical practice as non-invasive measurement tool for diagnosis of dry eye syndrome. Automation of our diagnosis tool could be achieved by using wavelet transform of the monitored data sequences.
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