Rheology of Tear Film Lipid Layer Spread in Normal and Aqueous Tear-Deficient Dry Eyes

• Published in: Investigative ophthalmology & visual science 2008-12, Vol.49 (12), p.5319-5324
• Main Authors: Yokoi, Norihiko, Yamada, Hideaki, Mizukusa, Yutaka, Bron, Anthony J, Tiffany, John M, Kato, Takahisa, Kinoshita, Shigeru
• Format: Article
• Language: English
• Subjects: Adult; Aged; Aged, 80 and over; Biological and medical sciences; Dry Eye Syndromes - metabolism; Eye and associated structures. Visual pathways and centers. Vision; Female; Fundamental and applied biological sciences. Psychology; Humans; Interferometry; Light; Lipid Metabolism - physiology; Male; Medical sciences; Middle Aged; Ophthalmology; Rheology; Tears - metabolism; Time Factors; Vertebrates: nervous system and sense organs
• ISSN: 0146-0404; 1552-5783; 1552-5783
• DOI: 10.1167/iovs.07-1407

To analyze the relationship between tear volume and tear film lipid layer (TFLL) spread. 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. In all cases, the time-dependent changes in TFLL spread could be described by the expression H(t) - H(0) = rho[1 - exp(-t/lambda)], where H(t) is the averaged height in millimeters at time t, H(0) is the averaged height at t = 0, rho is a constant, t is time in seconds, and lambda 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). 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.