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Daniel Russell Powell, Peter Ewen King-Smith, Heather L Chandler; Evaluation of tear film lipid layer (TFLL) thickness and tear thinning rates in cigarette smokers. Invest. Ophthalmol. Vis. Sci. 2014;55(13):39.
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© ARVO (1962-2015); The Authors (2016-present)
According to the Dry Eye Workshop Report, cigarette smoking has been identified as a potential risk factor for dry eye. The gaseous and particulate phases of tobacco smoke contain many oxidants and reactive oxygen species that may alter TFLL components, potentially resulting in increased tear evaporation. The study purpose was to determine whether smokers presented with decreased TFLL and, therefore, increased tear thinning rates compared to those who never smoked.
Eligible participants between 18-44 years of age who were not current contact lens wearers were enrolled. Smokers were required to have smoked on a daily basis for at least three years prior to the study. Nonsmokers must have worked and lived in a smoke-free environment. TFLL and tear thinning rate measurements of the pre-corneal tear film (25 μm X 35 μm) over a 20-second period were performed by a spectral interferometry technique described previously (King-Smith, 2002), then analyzed using SigmaPlot 10.0. Two trials were run three minutes apart and all outcomes were averaged and analyzed using Mann-Whitney U tests.
Sixty-five subjects were enrolled (20 smokers, 45 nonsmokers). Females comprised 55% of smokers and nonsmokers. Mean age for smokers and nonsmokers was 30.2 ± 6.5 and 26.6 ± 6.1 years, respectively. The TFLL of nonsmokers was marginally thicker than in smokers (49.8 ± 25.7 and 48.2 ± 22.6 nm, respectively), but the difference was not significant (p = 0.72). Mean tear thinning rates were over 60% greater in smokers than nonsmokers (7.0 ± 6.5 and 4.3 ± 2.3 µm/min, respectively), but were borderline nonsignificant (p = 0.07).
Smokers do not appear to present with a decreased TFLL, although it is plausible to postulate that smoke exposure may increase tear thinning rates compared to nonsmokers. It is possible that TFLL components are altered allowing for increased tear thinning without affecting TFLL thickness. Future studies involving increased participation of smokers, inclusion of smokers with high cumulative exposure (i.e., heavy smokers), inclusion of an objective measurement of smoke exposure (urinary cotinine levels), and an improved understanding of the TFLL and its role in tear evaporation, will be needed.
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