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Daniel Powell, Peter King-Smith, Heather Chandler; Observation of Spreading and Mechanical Properties of the Tear Film Lipid Layer Using A High Performance Video-Based Interferometry System. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6008.
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Interferometric-based imaging systems have demonstrated their usefulness in obtaining clinically-relevant information from the preocular tear film since the 1980’s. Camera resolution and image blur secondary to movement of the tear film lipid layer (TFLL) are among several limitations with these devices. The introduction of a high performance video-based interferometer (HPVI) can provide information on the spreading and mechanical characteristics of the TFLL not found in current imaging systems and includes a color key to indicate TFLL thickness.
The HPVI is capable of imaging a 6-mm diameter area of the pre-corneal tear film over a preselected time frame (40 sec). A video camera records images at 68 frames/sec at a resolution of 1400x1100 pixels and used in conjunction with a stroboscopic light source (<40µs duration) that minimizes image blurring secondary to eye and TFLL movements. A monitor provides immediate feedback on proper focusing and eye alignment. Imaging processing software records the time and duration of a blink which allows for TFLL evaluation immediately before, during, and after a blink. Subjects included non-contact lens wearing nonsmokers who never smoked and current smokers.
Images were obtained from 36 subjects between 20-42 years of age. TFLL wrinkling was observed below the upper lid during the downstroke of a blink (Fig. 1). Descension of the upper lid appeared to have compressed these wrinkles into concertina-like folds directly adjacent to the lid. A thick band of lipid appeared to deposit lipid into the TFLL early in the upstroke phase (Fig. 2, another subject). As the upstroke continued, there was a decrease in lipid deposition from the lower band, creating a lipid thickness gradient. With increasing time post-blink, upward drift of the TFLL appeared to reduce or eliminate this lipid thickness gradient. Finger-like features projecting downward from the upper TFLL likely represent meibum that had been secreted from the superior meibomian glands.
The HPVI offers several advantages over other imaging systems as described as well as a video camera with enhanced resolution and color contrast of the images by a factor of two. HPVI images may provide valuable clues on how the spreading and mechanical properties of the TFLL differ between non dry-eye individuals and those with evaporative dry eye.
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