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Norihiko Yokoi, Hideaki Yamada, Yutaka Mizukusa, Anthony J. Bron, John M. Tiffany, Takahisa Kato, Shigeru Kinoshita; Rheology of Tear Film Lipid Layer Spread in Normal and Aqueous Tear–Deficient Dry Eyes. Invest. Ophthalmol. Vis. Sci. 2008;49(12):5319-5324. doi: 10.1167/iovs.07-1407.
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purpose. To analyze the relationship between tear volume and tear film lipid layer (TFLL) spread.
methods. Twenty-nine eyes from 22 subjects, including normal eyes and eyes with aqueous tear–deficient dry eye, were enrolled in this study. In all eyes, the radius of curvature (R: mm) of the central lower tear meniscus was measured with a video-meniscometer, and interference images from the TFLL were recorded with a video-interferometer. Interference images were captured as still images every 0.05 second, and the relationship between the acquisition time for each image after a blink and the averaged heights of the spreading TFLL in the upstroke of the blink were calculated.
results. In all cases, the time-dependent changes in TFLL spread could be described by the expression H(t) − H(0) = ρ[1 − exp(−t/λ)], where H(t) is the averaged height in millimeters at time t, H(0) is the averaged height at t = 0, ρ is a constant, t is time in seconds, and λ is the characteristic time in seconds. A statistically significant correlation was found between those changes and the initial upward velocity of the spreading TFLL [H′(0) = dH(0)/dt] and R (r = 0.573; P = 0.003).
conclusions. This study demonstrated that the time-dependent changes of TFLL spread are compatible with the Voigt model of viscoelasticity and that the initial velocity of TFLL spread after a blink decreased in proportion to the decrease of tear volume. There is potential interest in using this parameter to diagnose and evaluate the severity of aqueous tear deficiency.
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