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    Glaucoma

    Using retrospective data from a cross-sectional health survey, investigators examined the association between consumption of caffeinated beverages and glaucoma.

    Study design

    Investigators used data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES). They analyzed the association between consumption of various caffeinated and decaffeinated beverages (i.e., coffee, iced tea, hot tea and soft drinks) and glaucoma (defined by the Rotterdam criteria).

    Outcomes

    After adjusting for glaucoma risk factors such as smoking status, body mass index and diabetes among a diverse sample of 1,678 American adults, the authors found no significant correlation between coffee or soft drink consumption—either caffeinated or noncaffeinated—and glaucoma.

    Conversely, daily consumption of hot, caffeinated tea was associated with a lower incidence of glaucoma (OR 0.26; P=0.010). This association was not seen with the consumption of iced tea or decaffeinated hot tea.

    Limitations

    This study was limited by its retrospective, observative and cross-sectional design. In addition, the questions did not explore the types of tea consumed (e.g., instant vs. brewed, black vs. green). Glaucoma diagnosis was based on visual field and optic nerve appearance, which are subject to misclassification bias with a 9% false-positive rate and 6% false-negative rate.

    Clinical significance

    Previous studies have shown contradictory results regarding the benefits and harms of coffee, tea and caffeine consumption. These results indicate the antioxidants found in tea—and not those in coffee—may be beneficial to eye health. However, further studies are certainly necessary before definitive recommendations can be made to patients.