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Editors Selection IGR 13-2

Clinical Forms of Glaucoma: Hypothyroidism and OAG

Comment by Louis Pasquale on:

27189 Hypothyroidism and the risk of developing open-angle glaucoma: A five-year population-based follow-up study, Lin H-C; Kang J-H; Jiang Y-D et al., Ophthalmology, 2010; 117: 1960-1966

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Lin et al. (1863) used a healthcare database to assess the relationship between hypothyroidism and open-angle glaucoma (OAG). This is a retrospective case (patients with hypothyroidism)- comparison (patients without hypothyroidism) analysis nested within a population-based sample. Both cases and comparison subjects were free of OAG at baseline and had a uniform five-year follow-up period. Patients who were hypothyroid had a statistically significant 1.8-fold increased risk of OAG relative to the comparison group after adjusting for multiple covariates. Untreated hypothyroid patients had a significant 2.3-fold increased risk of OAG relative to the comparison group. In hypothyroid patients treated with levothyroxine the risk was 1.7-fold, but it was not statistically significant. The authors do not provide a competing survival analysis between treated and untreated hypothyroidism (Glynn RJ, Rosner B. Am J Epidemiol 2005; 162: 975-982). Thus it is not possible to conclude that levothyroxine was protective against the development of OAG because the authors also do not show whether the relative risks for OAG among treated and untreated hypothyroidism patients are statistically different from one another. The reported association between hypothyroidism and OAG could be due detection bias since cases had more co-morbid conditions like diabetes mellitus and may have been under greater ophthalmic scrutiny. Multivariable analyses cannot overcome shortcomings introduced by detection bias. The study has strengths that included using a uniform follow-up period and minimizing the effect of reverse causation (the possibility that OAG occurred before hypothyroidism). There is certainly good biological rationale for other researchers to confirm and extend the findings of Lin and colleagues.

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