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Peter Ewen King-Smith, Kathleen S Reuter, Carolyn G Begley, Richard J Braun; Tear Film and Lipid Layer Structure in Relation to Four Phases of the Blink Cycle. Invest. Ophthalmol. Vis. Sci. 2014;55(13):38.
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To provide new or improved information about changes in tear film and lipid layer structure in relation to four phases of the blink cycle, namely, the down phase, the turning point, the up phase and the steady phase.
Images at different phases of the blink cycle were recorded from 27 subjects (21 female, age 43±17 yr) using a new stroboscopic microscope covering an area of 6 mm diameter and using a high performance color camera (1400 x 1100 pixels, 67 images/sec, flash duration 0.04 msec). Interpretation of results was aided by comparison to previous studies at Ohio State and Indiana Universities, including high resolution color microscopy, fluorescence imaging, retroillumination and wavefront sensing. Additionally, fluid dynamics modeling was used to test hypotheses of the origin of observed effects.
During the downstroke of the upper lid, wrinkling of the surface of the tear film was often observed, Evidence indicates that this wrinkling is caused by movement of the tear film over the rough corneal surface and a theory of this phenomenon will be presented. Also during the downstroke, the lid velocity was much greater than the downward velocity of the visible lipid layer, implying accumulation of a narrow and thick lipid band under the lid. At the "turning point" of a partial blink (lowest reach of the upper lid), a groove can be formed in the tear surface by mechanisms similar to the generation of the black-line near the meniscus (McDonald and Brubaker, 1971, Am J Ophthalmol, 72, 139). During the up phase, the lipid accumulated under the upper lid is initially released as a thick band, but later, the deposited lipid may become thinner as the accumulated lipid is depleted. In the steady phase, the lipid pattern is often very repeatable from blink to blink, but sometimes changes suddenly between two blinks (Bron et al., 2004, Exp Eye Res, 78, 347). Additionally, in our observations, the images may change greatly over a series of blinks, but each image is simply a distorted view of the previous image. Presumably the same lipid is imaged but after considerable movement as well as local stretching or compression, rotation and shearing.
Stroboscopic microscopy can provide novel information about structural changes in the tear film and lipid layer by eliminating blur from rapid tear film movement during the blink process.
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